Microfluidic Lab-on-a-Chip for Point-of-Care Veterinary Diagnostics

Overview and Principles of Microfluidic Lab-on-a-Chip for Point-of-Care Veterinary Diagnostics

The paradigm shift in veterinary diagnostics from centralized laboratory analysis to decentralized, real-time testing at the site of animal care is fundamentally enabled by microfluidic lab-on-a-chip (LOC) technology. These systems, which manipulate minute volumes of fluids-typically in the nanoliter to microliter range-within microfabricated channels, represent a convergence of engineering, materials science, and molecular biology. For the veterinary clinical pathologist, understanding the core principles of these platforms is essential for evaluating their diagnostic utility, interpreting their outputs, and anticipating their integration into clinical workflows. The overarching goal is to replicate or surpass the analytical performance of benchtop instruments while dramatically reducing time-to-result, sample volume requirements, operator dependency, and instrument cost [24, 28]. This section delineates the foundational principles governing microfluidic LOC systems as applied to point-of-care (POC) veterinary diagnostics, with a focus on fluidic control, sample processing, and detection modalities.

Foundational Principles of Microfluidic Manipulation

At its core, microfluidics exploits the unique behavior of fluids at the microscale, where surface forces, capillary action, and laminar flow dominate over inertial and gravitational forces. This regime allows for precise, reproducible, and automated handling of biological samples without the need for complex external actuators in many designs. The most fundamental operation is the controlled movement of fluids through microchannels, which can be achieved through several mechanisms. Capillary-driven microfluidics, often implemented in paper-based or open-channel devices, leverages the wicking force generated by hydrophilic surfaces to draw samples through the network without external power [27]. This principle is particularly attractive for resource-limited settings, as it eliminates the need for pumps or power sources. Centrifugal microfluidics, or lab-on-a-disc (LOAD) platforms, utilizes rotational forces to propel fluids radially outward through microchannels, with flow rates precisely controlled by spin speed and channel geometry [9]. This approach is highly amenable to parallel processing and sequential fluidic steps, such as metering, mixing, and valving, all controlled by a simple motor. Digital microfluidics (DMF) manipulates discrete droplets on an array of electrodes via electrowetting-on-dielectric (EWOD), allowing for individual droplet dispensing, merging, splitting, and transport without physical channels [5]. This offers exceptional reconfigurability and minimizes sample loss, as the sample itself serves as the reaction vessel.

The integration of passive valves is critical for automating multi-step assays without external control. Capillary burst valves, which rely on sudden changes in channel geometry or surface energy, can stop flow until a specific centrifugal or pneumatic pressure is exceeded [9]. Phase-change valves, utilizing materials like paraffin wax that melt upon heating, provide robust sealing for long-term storage of reagents. These valving strategies, combined with precise metering structures, enable the deterministic aliquoting of samples into multiple reaction chambers, a prerequisite for multiplexed analysis [9, 19]. The ability to perform on-chip sample preparation is a defining feature of advanced LOC systems. For blood-based diagnostics, microfluidic plasma separation is a critical first step, achieved through mechanisms such as size-exclusion filtration using micropillar arrays, membrane-based filtration, or the Zweifach-Fung effect in bifurcating channels, where cells preferentially travel into the higher-flow branch [25]. This eliminates the need for centrifugation, a major bottleneck in POC workflows. Similarly, nucleic acid extraction has been miniaturized using solid-phase extraction on silica beads, magnetic beads, or functionalized surfaces integrated within the microchannel, often driven by syringe pumps or integrated vacuum systems [1, 15]. A particularly innovative approach uses confined ultrasonic grinding within a microsphere-packed chamber to achieve rapid, chemical-free cell lysis and nucleic acid release [12].

Detection Modalities: Transducing Biological Events into Measurable Signals

The microfluidic chip is merely a reaction vessel; the diagnostic power is realized through integrated detection systems that convert the biological recognition event into a quantifiable signal. The choice of detection modality dictates the sensitivity, specificity, multiplexing capability, and overall complexity of the LOC system.

Nucleic acid amplification-based detection remains the cornerstone of molecular diagnostics, and its adaptation to microfluidics has been a major focus. Microfluidic PCR platforms have been engineered to overcome the challenges of rapid thermal cycling in small volumes. These include continuous-flow PCR, where the sample moves through zones of different temperatures, and stationary-chamber PCR with integrated thin-film heaters and Peltier elements for rapid heating and cooling [2, 4, 13]. The development of portable, battery-powered thermocyclers with ramp rates exceeding 1 degrees C/s demonstrates the feasibility of field-deployable PCR [2]. Solid-phase PCR (SP-PCR) immobilizes one primer on the chip surface, allowing for the spatial separation of amplicons and enabling high-level multiplexing, as demonstrated in a vertical microfluidic chip with an all-dielectric metasurface for enhanced fluorescence detection [15]. Isothermal amplification methods, particularly loop-mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA), are exceptionally well-suited for POC applications due to their constant-temperature operation, tolerance to inhibitors, and rapid amplification kinetics [7, 24]. Microfluidic LAMP chips have been developed for a wide range of veterinary pathogens, including Streptococcus equi subsp. equi in horses [20], multiple enteric coronaviruses in swine (Porcine Epidemic Diarrhea Virus, Porcine Deltacoronavirus) [21], and Avian Influenza Virus [16]. The integration of LAMP with CRISPR-Cas systems (e.g., Cas12a, Cas13a) provides an additional layer of specificity through sequence-specific trans-cleavage activity, converting amplified nucleic acids into a detectable signal [7, 10]. This one-tube integration, however, requires careful engineering to address biochemical incompatibilities between the amplification and CRISPR components, with strategies including spatial isolation, phase separation, and optimized reaction chemistry [10].

Immunoassay-based detection on microfluidic platforms offers a direct route to protein biomarker quantification. The luminescent oxygen channeling immunoassay (LOCI) integrated with digital microfluidics (iDMF-mLOCI) represents a wash-free, homogeneous assay format that achieves sub-picogram per milliliter sensitivity for sepsis biomarkers using only 2.2 microliters of plasma [5]. Hollow-core fiber (HCF) optofluidic chips provide an alternative approach, where the inner wall of the fiber is functionalized with capture antibodies, and the long, confined microchannel enhances analyte capture efficiency and light-matter interaction, enabling rapid (10-minute) detection of influenza A antigen with a limit of detection of 2.41 pg/mL [14]. Nanobody-based immunoassays, combined with 3D-printed microfluidic chips and smartphone detection, offer a portable and reusable platform for virus detection, as demonstrated for H7N9 Avian Influenza Virus [16]. Label-free detection using photonic integrated circuits (PICs) represents a paradigm shift, where the binding of viral particles to functionalized sensor surfaces directly alters the refractive index, which is transduced into an optical signal [17, 18]. This approach has been validated for the pen-side detection of African Swine Fever Virus, Classical Swine Fever Virus, Porcine Reproductive and Respiratory Syndrome Virus, and Swine Influenza A Virus, eliminating the need for labeled reagents and simplifying the assay workflow [17, 18].

Electrochemical biosensors offer high sensitivity, low cost, and compatibility with miniaturized electronics, making them attractive for POC applications. These sensors typically employ a biorecognition element (antibody, aptamer, or nucleic acid probe) immobilized on an electrode surface. Target binding is transduced through changes in current, potential, or impedance [6, 26]. The integration of electrochemical sensors with microfluidics enables precise control over sample delivery and washing steps, improving reproducibility and reducing non-specific binding [26]. For antimicrobial susceptibility testing (AST), microfluidic platforms can generate precise antibiotic concentration gradients and monitor bacterial growth in real-time, providing rapid phenotypic resistance profiles within hours rather than days [19, 26].

Signal Readout and Data Integration

The final critical component of a POC LOC system is the readout mechanism. While visual inspection of colorimetric signals (e.g., from LAMP or lateral flow assays) is the simplest, it is subjective and semi-quantitative [8]. Smartphone-based detection has emerged as a powerful solution, leveraging the ubiquitous camera, processing power, and connectivity of modern smartphones. Custom-designed cradles or attachments provide controlled illumination and optics, while dedicated applications perform automated image analysis, quantification, and data transmission to cloud-based databases for epidemiological surveillance [11, 22, 23]. Deep learning algorithms further enhance this capability by enabling ratiometric signal transduction, which corrects for ambient light variations and improves analytical sensitivity by an order of magnitude compared to visual interpretation [3]. The integration of artificial intelligence and machine learning (AI/ML) with Internet of Things (IoT) connectivity is poised to transform LOC systems from simple diagnostic tools into intelligent, networked platforms capable of predictive analytics and real-time outbreak monitoring [11]. This convergence of microfluidics, advanced detection, and digital health represents the ultimate realization of the POC vision in veterinary medicine.

Molecular Pathogenesis and Detection Mechanisms: Nucleic Acid Amplification and Immunoassay Integration

The architectural convergence of nucleic acid amplification and immunoassay-based detection within microfluidic lab-on-a-chip (LOC) platforms represents a paradigm shift in point-of-care (POC) veterinary diagnostics. From a clinical pathologist's perspective, the molecular pathogenesis of infectious disease in animals is fundamentally a narrative of pathogen invasion, replication, and host immune response-each stage presenting distinct diagnostic windows and analytical targets. The integration of nucleic acid amplification tests (NAATs) and immunoassays on a single microfluidic substrate is not merely a technical convenience; it is a biological necessity dictated by the temporal kinetics of infection, the variable shedding patterns of pathogens, and the differential diagnostic requirements across species. This section provides an exhaustive analysis of the molecular principles, technological implementations, and integration strategies that underpin these dual detection modalities, with a critical focus on their application to veterinary pathogens, including those affecting aquatic species, poultry, livestock, companion animals, and wildlife.

Nucleic Acid Amplification Strategies within Microfluidic Architectures

The detection of pathogen nucleic acids-whether DNA or RNA-remains the most sensitive and specific approach for diagnosing active infections, particularly during the acute phase when pathogen load may be low and seroconversion has not yet occurred. The translation of amplification chemistries to microfluidic platforms demands meticulous attention to fluid dynamics, thermal management, and reagent stabilization, each of which directly influences analytical performance in field settings.

Polymerase Chain Reaction (PCR) and Its Microfluidic Derivatives

Conventional PCR, while robust in centralized laboratories, presents significant challenges for miniaturization, including the need for precise thermal cycling, prevention of evaporation in low-volume reactions, and mitigation of bubble formation during heating. Recent innovations have addressed these constraints through novel chip architectures and thermal engineering. The thin-film microfluidic system described by Cheng et al. [1] integrates chemical lysis, alcohol-free nucleic acid purification, multiplex asymmetric PCR (AS-PCR), and CRISPR-Cas12a detection within a fully sealed platform, achieving a detection limit of 1 CFU/mL for Mycobacterium tuberculosis and completing the entire sample-to-answer workflow in 78 minutes. This system is particularly instructive for veterinary applications, as it demonstrates the feasibility of POC genotyping of drug-resistance mutations-a capability directly translatable to pathogens such as Bovine Viral Diarrhea Virus and Porcine Reproductive and Respiratory Syndrome Virus, where quasispecies dynamics and vaccine strain differentiation demand sequence-level discrimination.

The development of portable, battery-powered thermocyclers has further expanded the deployment envelope for PCR-based diagnostics. Mahardika et al. [2] reported a handheld POCT-PCR device weighing 1.0 kg with a manufacturing cost of US$97, capable of ramp rates of +1.10 degrees C/s and -1.95 degrees C/s, enabling 30 cycles of amplification in 78 minutes. This system, validated for cyanobacterial gene detection, employs custom mini-PCR tubes (30 microliter capacity) to enhance thermal transfer and minimize evaporation-a critical design consideration for veterinary field use where environmental temperature extremes may be encountered. Similarly, Lee et al. [13] developed a portable real-time PCR system for airborne bacterial detection that demonstrated limits of detection ranging from 6.0 x 10^0 to 6.0 x 10^1 CFU/mL for Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, and Micrococcus luteus, with overall assay completion within 2 hours. The two-stage amplification strategy employed in this system is particularly relevant for detecting low-abundance targets in complex matrices such as oral fluids, nasal swabs, and fecal samples commonly encountered in veterinary practice.

Quantitative PCR (qPCR) on microfluidic platforms has matured to the point of commercial viability, as evidenced by the Q3-Plus V2 platform evaluated for canine leishmaniasis diagnosis by Latrofa et al. [29]. This lab-on-chip real-time PCR system demonstrated overlapping quantification cycle (Cq) values with benchtop CFX96 instrumentation for Leishmania infantum detection across multiple sample types (bone marrow, lymph node, blood, buffy coat, conjunctival swab, skin), achieving a limit of detection below 1 promastigote per milliliter. Notably, the platform showed higher sensitivity for non-extracted samples (NES), bypassing the DNA extraction step entirely-a significant advantage for POC deployment where extraction infrastructure may be unavailable. The transfer of qPCR assays to microfluidic formats requires systematic optimization, as demonstrated by Pereira et al. [4] for Staphylococcus aureus enterotoxin gene cluster detection. Using design of experiments (DoE) methodology, these investigators identified polymerase and primer concentrations as the most influential factors affecting amplification efficiency, achieving detection of 4 to 40,000 template copies in 1.8 microliter reaction volume within 19 minutes-a substantial reduction from the 40-minute run time required by conventional real-time PCR platforms.

Solid-phase PCR (SP-PCR) represents an emerging paradigm that addresses the multiplexing limitations of solution-phase amplification. Seder et al. [15] engineered a vertical microfluidic chip integrating SP-PCR with all-dielectric nanostructured metasurfaces, achieving a detection limit of 10 copies/reaction for multiplexed pathogen detection. The vertical chip orientation, combined with gravity-assisted fluid dynamics and a dual-heater configuration, eliminates bubble formation during thermal cycling-a persistent challenge in microfluidic PCR-and enables subsecond thermal transitions without active cooling. This architecture holds particular promise for veterinary applications requiring simultaneous detection of multiple pathogens from a single sample, such as respiratory disease panels in cattle or enteric pathogen screening in swine.

Isothermal Amplification: LAMP, RPA, and NASBA in Microfluidic Formats

The logistical demands of POC veterinary diagnostics-rapid turnaround, minimal instrumentation, tolerance to sample impurities-have positioned isothermal amplification methods as the workhorses of microfluidic NAAT platforms. Loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), and nucleic acid sequence-based amplification (NASBA) each offer distinct advantages and limitations that must be carefully matched to the target pathogen and diagnostic context.

LAMP, with its high amplification efficiency (>10^9-fold in 30-60 minutes) and tolerance to common PCR inhibitors, has been widely adopted for microfluidic integration. The fundamental principle of LAMP relies on auto-cycling strand displacement DNA synthesis mediated by Bst polymerase and four to six primers recognizing six to eight distinct regions of the target sequence. This high primer complexity confers exceptional specificity but also increases the risk of non-specific amplification-a challenge that must be addressed through rigorous primer design [7]. The microfluidic LAMP chip developed by Zhou et al. [21] for simultaneous detection of Porcine Epidemic Diarrhea Virus, Porcine Deltacoronavirus, and swine acute diarrhea syndrome coronavirus achieved detection limits of 10^1, 10^2, and 10^2 copies/microliter, respectively, with a total assay time of 40 minutes and no cross-reactivity with other common swine viruses. Evaluation of 173 clinical fecal samples demonstrated 100% specificity and sensitivities exceeding 91% for all three targets, with coefficients of variation below 5%.

The integration of LAMP with smartphone-based detection has further democratized POC diagnostics. The platform developed by Sun et al. [22] and Chen et al. [23] for equine respiratory pathogens-including Equine Influenza A Virus, Equine Herpesvirus 1, and Streptococcus equi subsp. equi-utilizes a microfluidic chip with pre-deposited LAMP reagents in distinct lanes, generating fluorescent products that are excited by LEDs and detected by a smartphone camera. The system processes a single 15 microliter droplet of test sample within 30 minutes, with detection limits comparable to laboratory-based PCR. The integration of cloud-based data reporting for epidemiological surveillance represents a critical advancement for veterinary outbreak response, enabling real-time geolocation of positive cases and coordination of control measures.

RPA offers several advantages over LAMP for microfluidic integration, including lower reaction temperatures (37-42 degrees C), simplified primer design (typically two primers), and faster amplification kinetics. However, the biochemical incompatibility between RPA and downstream detection systems-particularly CRISPR-Cas enzymes-presents a significant challenge for one-tube integration. Liu et al. [10] systematically reviewed five strategies to address this incompatibility: spatial isolation (using physical barriers or phase-change materials), phase separation (via density/viscosity modifiers or agarose gel), microfluidics (centrifugal, capillary, electric, or pressure-driven), crRNA design/modification, and reaction component optimization. For veterinary applications, the microfluidic approach appears most promising, as it allows physical separation of RPA and CRISPR components while maintaining fluidic connectivity for sequential reactions. The thin-film microfluidic system described by Cheng et al. [1] exemplifies this approach, integrating asymmetric PCR with PAM-independent CRISPR-Cas12a detection through coordinated dual-signal readout, enabling accurate identification of seven clinically relevant rpoB mutations in Mycobacterium tuberculosis with a mutant allele frequency detection threshold of 20%.

CRISPR-Cas-Based Detection: The Next Frontier

The repurposing of CRISPR-Cas systems for nucleic acid detection has introduced a transformative capability for POC diagnostics: programmable sequence-specific recognition coupled with collateral cleavage activity that generates an amplifiable signal. Cas12a (targeting DNA) and Cas13a (targeting RNA) are the most commonly employed effectors, with Cas9 also finding applications in specific detection formats [7, 24]. The integration of CRISPR-Cas detection with isothermal amplification in microfluidic formats presents unique challenges and opportunities. The design principles articulated by Silva et al. [7] emphasize the critical importance of target sequence selection, guide RNA optimization, and probe format selection (e.g., fluorophore-quencher, lateral flow, electrochemical) for achieving robust assay performance. The high risk of false-positive results in LAMP-CRISPR assays, arising from non-specific amplification and trans-cleavage activity, necessitates rigorous standardization including no-template controls, melt curve analysis, and orthogonal confirmation methods.

The potential of CRISPR-based diagnostics for veterinary pathogens is particularly evident in applications requiring discrimination of closely related genotypes or vaccine strains. For Avian Influenza Virus, where low-pathogenicity and high-pathogenicity strains differ by a single amino acid residue at the hemagglutinin cleavage site, CRISPR-Cas systems can potentially achieve the sequence-level discrimination required for virulence determination. Similarly, for Foot-and-Mouth Disease Virus, where seven serotypes exist with limited cross-protection, CRISPR-based serotyping could enable rapid selection of appropriate vaccine strains and inform control strategies.

Immunoassay Integration: Direct Antigen and Antibody Detection

While NAATs provide definitive evidence of pathogen presence, immunoassays offer complementary diagnostic information, including detection of soluble antigens in early infection, identification of antibodies indicating exposure or vaccination, and quantification of host immune biomarkers indicative of disease severity or prognosis. The integration of immunoassays with microfluidic platforms requires fundamentally different engineering approaches than nucleic acid amplification, reflecting the distinct biophysical properties of protein targets and antibody reagents.

Lateral Flow and Paper-Based Immunoassays

The lateral flow assay (LFA) remains the most widely deployed POC immunoassay format in veterinary medicine, owing to its simplicity, low cost, and equipment-free operation. However, conventional LFAs suffer from limited sensitivity (typically 10^6-10^8 target molecules/mL) and qualitative or semi-quantitative readout. The integration of LFAs with microfluidic sample preparation modules, signal amplification strategies, and smartphone-based quantification has substantially enhanced their analytical performance. The paper-based microfluidic devices reviewed by Mao et al. [27] demonstrate the potential of isothermal amplification integration with lateral flow readout for LAMP-based detection of foodborne pathogens and veterinary disease agents. The device presented by Panich et al. [8] for multiplex detection of gastrointestinal helminth parasites (including Raillietina species and Ascaridia galli) integrates power-free sample loading, colorimetric LAMP, and chromatic analysis via image processing, achieving strong agreement with the gold standard method (Cohen's kappa value = 0.9) and minimum detectable DNA concentrations ranging from 4 ng to 40 pg/chip.

Microfluidic Immunoassays with Enhanced Sensitivity

The transition from paper-based to chip-based immunoassays enables more sophisticated fluid handling, higher surface-to-volume ratios for capture, and integration with sensitive detection modalities. The hollow-core fiber (HCF) optofluidic immunosensor reported by Ren et al. [14] exemplifies the potential of microfluidic immunoassay for rapid, high-sensitivity detection. This all-fiber platform eliminates external pumps and tubing by using a standard fiber inserted into the HCF for direct light coupling, with the gap between fibers serving as the sample inlet. The inner wall of the HCF, functionalized with capture antibodies, provides an extremely high surface-to-volume ratio that shortens analyte diffusion distances and prolongs residence time, markedly improving antibody-capture efficiency. Quantitative detection of influenza A antigen was completed within 10 minutes without pre-incubation, achieving a limit of detection of 2.41 pg/mL-several orders of magnitude lower than conventional LFAs.

The centrifugal microfluidic disc developed by Dehghan et al. [9] for simultaneous ABO/Rh blood typing and hemoglobin quantification demonstrates the integration of multiple immunoassay modalities on a single platform. This system processes 12 microliters of whole blood and completes the full analytical workflow in 130 seconds, incorporating deterministic cascading aliquoting, Sephadex-treated passive siphon valves for whole-blood transfer, on-disc gel column agglutination for blood typing, and TMB-based colorimetric assay for hemoglobin quantification. Validation with 32 clinical samples demonstrated 100% sensitivity and 97.7% specificity for automated agglutination detection, with strong agreement for hemoglobin measurements (R^2 = 0.95). This platform's "power-independent architecture" is particularly attractive for veterinary field deployment, where electrical infrastructure may be unreliable.

Nanobody-Based Immunoassays and Photonic Integration

The use of nanobodies-single-domain antibody fragments derived from camelid heavy-chain antibodies-as capture and detection reagents offers several advantages over conventional monoclonal antibodies for microfluidic immunoassays. Nanobodies possess superior thermal stability, solubility, and refolding capacity, making them ideal for integration with microfluidic platforms that may experience temperature fluctuations during transport or operation. Ji et al. [16] generated a pair of nanobodies with high specificity and affinity for H7N9 Avian Influenza Virus and integrated them into a 3D-printed flower-shaped microfluidic chip with micropillar arrays to enhance surface area for immobilization. The resulting colorimetric immunoassay, quantified using smartphone imaging without external lighting, achieved a limit of detection of 5.9 x 10^3 EID50/0.1 mL-comparable to traditional ELISA-and demonstrated nine reuse cycles without significant sensitivity loss.

The integration of photonic integrated circuits (PICs) with microfluidics represents the cutting edge of label-free immunoassay detection. Manessis et al. [17, 18] developed POC devices incorporating PICs, microfluidics, and information and communication technology for field diagnosis of African Swine Fever Virus, Classical Swine Fever Virus, Porcine Reproductive and Respiratory Syndrome Virus, and Swine Influenza A Virus. These devices detect viral particles directly in oral fluid and serum samples through changes in refractive index at the sensor surface, without requiring enzymatic amplification or labeled reagents. For ASF and CSF, the device achieved sensitivities of 80.97% and 79%, specificities of 88.46% and 79.07%, and diagnostic odds ratios of 32.25 and 14.21, respectively, using PCR as the reference method. For PRRSV and SIV, sensitivities were 83.5% and 81.8%, with specificities of 77.8% and 82.2%. While these performance metrics are lower than those typically reported for laboratory-based assays, they must be contextualized within the operational realities of pen-side testing, where speed, simplicity, and robustness are prioritized over absolute analytical sensitivity.

Integrated Dual-Modality Platforms: Bridging Molecular and Immunological Detection

The ultimate diagnostic power of microfluidic LOC platforms lies in their capacity to integrate nucleic acid amplification and immunoassay detection within a single device, enabling simultaneous or sequential interrogation of both pathogen nucleic acids and host or pathogen proteins. This dual-modality approach addresses the fundamental biological reality that diagnostic sensitivity varies across infection stages-NAATs are most sensitive during acute replication, while serological assays detect past exposure or chronic carriage-and provides orthogonal confirmation of test results.

The integrated digital microfluidic platform for multiplexed luminescence oxygen channeling immunoassay (iDMF-mLOCI) reported by Li et al. [5] exemplifies this paradigm. This system leverages precise droplet manipulation on a digital microfluidic (DMF) platform to create a wash-free, multiplexed suspension assay for protein biomarkers, achieving limits of detection of 2.2 pg/mL for interleukin-6, 0.05 ng/mL for procalcitonin, and 0.2 ng/mL for heparin-binding protein using only 2.2 microliters of sample per test. While developed for human sepsis diagnosis, the underlying technology is directly transferable to veterinary applications, where multiplexed biomarker panels (e.g., acute phase proteins, cytokines, organ-specific enzymes) could provide prognostic and therapeutic monitoring information complementary to pathogen detection.

The integration of sample preparation modules-including plasma separation, nucleic acid extraction, and reagent storage-is critical for achieving true sample-to-answer functionality. Tarim et al. [25] reviewed emerging microfluidic plasma separation technologies that move beyond conventional centrifugation, including membrane-based filtration, acoustophoresis, dielectrophoresis, and deterministic lateral displacement. For veterinary applications, the ability to process whole blood, oral fluid, fecal suspensions, and tissue homogenates without pre-processing is essential for field deployment. The green confinement ultrasonic grinding approach reported by Jia et al. [12] achieves nucleic acid extraction from bacterial cells using selected acrylonitrile butadiene styrene spheres under common ultrasonic cleaner, achieving lysis efficiency over

Design and Fabrication of Microfluidic Platforms for Multiplex Pathogen Detection

The transition from single-analyte detection to high-order multiplexing is the defining challenge in modern veterinary point-of-care (POC) diagnostics. A microfluidic lab-on-a-chip (LOC) that can simultaneously interrogate a clinical sample for a panel of viral, bacterial, and parasitic pathogens must integrate sophisticated fluidic architecture with robust, mutually compatible biochemical reactions. The design and fabrication of such platforms require a deep understanding of materials science, surface chemistry, thermal management, and micro-architecture to ensure that each detection channel performs with equivalent sensitivity and specificity. This section provides an exhaustive examination of the core design principles, fabrication strategies, and integration technologies that underpin multiplex microfluidic platforms for veterinary diagnostics, drawing upon the most recent advances in the field.

Foundational Design Architectures for Multiplexing

The foundational decision in developing any multiplex microfluidic platform is the selection of a fluidic architecture that can partition a single sample into multiple reaction chambers without cross-contamination or dilution bias. A particularly elegant solution is the deterministic cascading aliquoting architecture, masterfully demonstrated in a centrifugal microfluidic disc for simultaneous blood typing and hemoglobin quantification [9]. In this design, a single 12 microliter whole-blood sample is metered into multiple 2 microliter reaction chambers through a series of passive siphon valves treated with Sephadex, achieving 100% priming success without any external actuation [9]. This architecture is power-independent, relying solely on centrifugal force from a programmable rotational protocol, and it processes the entire analytical workflow-from sample loading to gel column agglutination and colorimetric readout-in 130 seconds [9]. For veterinary field applications, where power availability is inconsistent, such passive, self-priming designs are invaluable.

Another paradigm-shifting approach is the use of vertical microfluidic chips that leverage gravity-assisted fluid dynamics to eliminate bubble formation during polymerase chain reaction (PCR) thermocycling. Seder et al. [15] engineered a vertical chip with preloaded reagent chambers for sequential lysis, washing, elution, and amplification, driven by a synchronized stepper motor and air vacuum. The vertical orientation ensures that any gas bubbles generated during heating rise harmlessly to the top of the chamber rather than adhering to the sensing surface, which had previously been a critical barrier to integrating solid-phase PCR into POC devices [15]. This chip incorporates an all-dielectric nanostructured metasurface beneath the PCR chamber to enable multiplexed solid-phase PCR, achieving a detection limit of 10 copies/reaction [15]. The dual-heater configuration alternates at subsecond intervals, obviating the need for active cooling and reducing overall reaction time, a critical feature for pen-side testing.

Fabrication Materials and Techniques: From Soft Lithography to 3D Printing

The choice of fabrication material and technique directly dictates the device's cost, scalability, biocompatibility, and optical clarity. Traditionally, polydimethylsiloxane (PDMS) has dominated academic microfluidics due to its gas permeability and optical transparency, but its incompatibility with organic solvents and tendency to absorb small hydrophobic molecules limits its utility in long-term veterinary applications. More recent work has shifted toward thermoplastics such as cyclic olefin copolymer (COC) and poly(methyl methacrylate) (PMMA), which offer superior chemical resistance and are amenable to mass production via injection molding.

A revolutionary fabrication technology that is transforming veterinary POC diagnostics is projection micro-stereolithography (PmicroSL) 3D printing. Ji et al. [16] utilized PmicroSL to fabricate a flower-shaped microfluidic chip integrating a micropillar array that dramatically increases the surface area for nanobody immobilization. This chip, designed for the detection of H7N9 Avian Influenza Virus, demonstrates that 3D printing can create complex, high-aspect-ratio structures that are impossible to achieve with traditional soft lithography [16]. The printed chip was reusable up to nine cycles without significant loss of sensitivity, which is a critical economic consideration for resource-limited veterinary clinics. Furthermore, the integration of smartphone-based detection with this 3D-printed chip eliminates the need for external lighting devices, directly linking advanced manufacturing with ubiquitous consumer electronics [16]. The ability to rapidly iterate chip designs through 3D printing also accelerates the optimization of fluidic geometries for specific veterinary matrices, such as the viscous oral fluids or fecal suspensions commonly encountered in field diagnostics.

Integration of Sample Processing with Thin-Film and Paper-Based Substrates

The fabrication of microfluidic platforms must address the "sample-to-answer" gap, particularly the upstream steps of nucleic acid extraction and purification, which are often the most technically demanding for field operators. A landmark achievement in this domain is the thin-film microfluidic system developed by Cheng et al. [1], which integrates chemical lysis, alcohol-free nucleic acid purification, multiplex asymmetric PCR, and PAM-independent CRISPR-Cas12a detection within a fully sealed platform. The thin-film format is fabricated by patterning silicon substrates with microfluidic channels and reaction chambers, over which a thin, flexible polymeric film is bonded to create a closed system. This design minimizes dead volumes and enables rapid thermal transfer, achieving a total turnaround time of 78 minutes for the entire workflow [1]. The alcohol-free purification step is particularly noteworthy, as it eliminates the need for flammable reagents that are hazardous in field settings. The system was validated for detecting rifampicin resistance mutations in Mycobacterium tuberculosis, but the architecture is directly translatable to veterinary pathogens such as Bovine Tuberculosis or Avian Tuberculosis, where genotyping of drug resistance is of increasing clinical importance.

At the opposite end of the fabrication cost spectrum, paper-based microfluidics offers an exceptionally low-cost and disposable alternative for multiplex detection. Panich et al. [8] developed a power-free sample-loading microfluidic chip integrated with colorimetric loop-mediated isothermal amplification (LAMP) for the simultaneous detection of five parasitic groups in poultry. The chip is fabricated by patterning hydrophobic barriers on cellulose paper using wax printing, creating hydrophilic channels that wick the sample via capillary action. The power-free nature of this system is a critical enabler for remote veterinary clinics in low-resource settings [8]. The colorimetric results can be interpreted with the naked eye or by chromatic analysis via a smartphone, achieving Cohen's kappa values of 0.9 when compared to gold standard morphological identification [8]. The minimum detectable DNA concentrations ranged from 4 ng to 40 pg per chip, demonstrating that paper-based platforms can achieve analytical sensitivity comparable to plastic-based systems. However, the inherent challenges of paper-such as variability in pore size, non-specific binding, and limited reagent stability-require careful mitigation through optimized wax deposition and the use of blocking agents like bovine serum albumin or polyethylene glycol [27].

Thermal Cycling and Isothermal Heating Integration

The fabrication of microfluidic platforms for PCR-based multiplex detection demands exquisite thermal management, as the thermal mass of the device and the heat transfer characteristics of the substrate directly impact cycle times and reaction efficiency. For field-deployable systems, achieving rapid thermal cycling without bulky Peltier elements is a major engineering challenge. Mahardika et al. [2] addressed this by fabricating a handheld, battery-powered PCR thermocycler weighing only 1.0 kg. The system integrates an aluminum heat sink, dual ceramic heaters, a Peltier-based cooling module, and a fast-response thermistor, all governed by Arduino-based PID control [2]. The use of custom mini-PCR tubes with a 30 microliter capacity, substantially smaller than conventional 100 microliter tubes, enhances thermal transfer and minimizes evaporation. The device achieves ramp rates of +1.10 degrees C/s and -1.95 degrees C/s, enabling 30 cycles in 78 minutes, a performance that is competitive with benchtop systems [2]. This thermocycler was validated for detecting eleven cyanobacterial genes, but the same thermal architecture can be directly adapted for a multiplex veterinary PCR chip targeting pathogens such as Avian Influenza Virus, Newcastle Disease Virus, and Infectious Bronchitis Virus.

For isothermal amplification methods like LAMP and recombinase polymerase amplification (RPA), the fabrication requirements shift from rapid cycling to stable, uniform heating at a single temperature. The integration of LAMP with CRISPR-Cas systems introduces additional complexity, as the trans-cleavage activity of Cas12a and Cas13a can be biochemically incompatible with the RPA or LAMP reagents if mixed freely in solution [7, 10]. Several fabrication strategies have been developed to achieve spatial or temporal isolation of the two reactions within a single microfluidic device. Liu et al. [10] systematically summarize five key strategies: spatial isolation via physical barriers or phase-change materials, phase separation using density or viscosity modifiers, microfluidics driven by centrifugal or capillary forces, crRNA design optimization, and reaction component optimization. For a veterinary multiplex chip, the spatial isolation approach is particularly attractive, as it allows the LAMP amplification to occur in one set of chambers before the amplicons are shunted to a second set of chambers containing the CRISPR detection reagents. This was effectively demonstrated by Zhou et al. [21] in a microfluidic-RT-LAMP chip for detecting Porcine Epidemic Diarrhea Virus, Porcine Deltacoronavirus, and Swine Acute Diarrhea Syndrome Coronavirus. The chip was fabricated using a silicon substrate with patterned channels and chambers, employing a centrifugal microfluidic design to sequentially move reagents through the amplification and detection zones without operator intervention [21].

Signal Transduction and Readout Integration in Fabricated Chips

The sensitivity of a multiplex microfluidic platform is ultimately limited by the efficiency of signal transduction and the robustness of the readout method. For label-free detection, photonic integrated circuits (PICs) represent a transformative fabrication technology. Manessis et al. [17, 18] developed a POC device incorporating PICs, microfluidics, and information and communication technology for the detection of African Swine Fever Virus and Classical Swine Fever Virus, as well as Porcine Reproductive and Respiratory Syndrome Virus and Swine Influenza A Virus. The PICs are fabricated on a silicon-on-insulator platform, employing submicron waveguide structures that are highly sensitive to changes in the refractive index caused by the binding of viral particles to functionalized waveguide surfaces [17]. The microfluidic channels are fabricated from a biocompatible polymer and bonded directly to the PIC chip, creating a hybrid optofluidic system. The devices achieved sensitivities of 80.97% and 83.5% for ASFV and PRRSV, respectively, when validated against reference PCR methods using oral fluid and serum samples from infected swine [17, 18]. The label-free approach eliminates the need for fluorescent labels or enzymatic amplification, simplifying the fabrication and reducing reagent costs, although the requirement for stringent temperature control and vibration-free operation remains a barrier to true field deployment.

For fluorescence-based detection, the integration of nanostructured surfaces directly into the microfluidic chip during fabrication can dramatically enhance signal strength. Ren et al. [14] proposed an all-fiber optofluidic immunosensor based on a hollow-core fiber (HCF) that integrates the entire assay onto a single microfluidic chip. The inner wall of the HCF is functionalized with capture antibodies, providing an extremely high surface-to-volume ratio. Coaxial propagation of both light and the sample inside the HCF strengthens light-matter interaction and enhances fluorescence collection efficiency, achieving a limit of detection of 2.41 pg/mL for influenza A antigen within 10 minutes [14]. This fiber-in-fiber fabrication approach eliminates external pumps and tubing, as a standard optical fiber is inserted into the HCF for direct light coupling, and the gap between the two fibers serves as the sample inlet. The resulting device successfully breaks the conventional sensitivity-versus-speed trade-off, offering a promising solution for rapid POC clinical diagnostics in veterinary settings where speed is paramount, such as during an outbreak of Highly Pathogenic Avian Influenza.

Addressing the Challenges of Reagent Storage and Stability

A common oversight in the fabrication of multiplex microfluidic chips is the long-term storage and stability of the preloaded reagents, particularly for field devices that may sit on a shelf for months before use. The state of the art involves the use of lyophilized (freeze-dried) reagent pellets that are integrated directly into the chip during the fabrication process. Zhou et al. [21] demonstrated that pre-storing RT-LAMP reagents in the chambers of their centrifugal microfluidic chip maintained full reactivity for at least 30 days at 4 degrees C. Chen et al. [23] took this a step further by pre-depositing LAMP reagents into distinct lanes of a silicon-based microfluidic chip embedded in a credit-card-sized cartridge, with the reagents remaining stable for weeks at room temperature. For the CRISPR-Cas components, which are particularly labile, the use of sucrose or trehalose as cryoprotectants during lyophilization has become standard practice [7]. The fabrication of the chip must therefore incorporate airtight seals, often achieved through laser welding or adhesive tapes with low moisture vapor transmission rates, to protect the lyophilized reagents from humidity. Additionally, the inclusion of desiccant chambers within the cartridge packaging can extend the shelf life to months, which is essential for veterinary applications in remote livestock operations where frequent resupply is not feasible.

In summation, the design and fabrication of microfluidic platforms for multiplex pathogen detection in veterinary medicine is a multi-faceted engineering challenge that demands consideration of fluid dynamics, thermal management, material biocompatibility, and reagent stability. The most successful platforms are those that integrate sample processing, amplification, and detection within a single, sealed device, minimizing user intervention and the risk of cross-contamination. As fabrication techniques such as 3D printing, thin-film silicon processing, and paper-based microfluidics continue to mature, the scalability and affordability of these devices will improve, paving the way for their widespread adoption in veterinary POC diagnostics.

Protocol and Methodology for Sample Processing and Assay Execution

The translation of a microfluidic lab-on-a-chip (LOC) platform from a conceptual prototype to a clinically deployable point-of-care (POC) diagnostic system hinges critically on the robustness, integration, and standardization of its underlying protocols for sample processing and assay execution. In veterinary medicine, where patients range from companion animals to livestock and aquatic species, the diversity of biological matrices-whole blood, serum, plasma, oral fluid, nasal swab eluates, guttural pouch lavage, fecal suspensions, tissue homogenates, and even environmental water samples-imposes unique demands on the front-end of any diagnostic workflow. The following section delineates the comprehensive methodological framework for sample processing, nucleic acid extraction, amplification, and detection within integrated microfluidic systems, drawing upon the latest advances in the field.

3.1 Sample Collection, Preprocessing, and Microfluidic Front-End Integration

The initial step in any POC diagnostic protocol is the acquisition and preparation of the clinical specimen. For blood-based assays, the separation of plasma or serum from cellular components is a prerequisite for most downstream analyses, including serological and molecular tests. Traditional centrifugation is impractical in field settings, necessitating the development of microfluidic plasma separation technologies. Recent innovations have demonstrated that deterministic cascading aliquoting architectures, such as those employed in centrifugal microfluidic discs, can process 12 microliters of whole blood to yield plasma for downstream analysis within 130 seconds, utilizing Sephadex-treated passive siphon valves that achieve 100% priming success without external actuation [9]. Similarly, emerging microfluidic designs leverage size-exclusion membranes, hydrodynamic filtration, and acoustic or dielectrophoretic forces to achieve rapid plasma separation from finger-stick volumes, effectively bypassing the need for benchtop centrifuges [25]. For respiratory pathogens, nasal swab or guttural pouch lavage specimens are often collected directly into lysis or stabilization buffers. In the context of Streptococcus equi subsp. equi detection, guttural pouch lavage samples have been successfully processed directly on a LAMP microfluidic device without prior DNA extraction, demonstrating the feasibility of direct sample-to-answer workflows [20]. For enteric pathogens, fecal samples require homogenization and clarification to remove particulate matter that could obstruct microchannels. A power-free sample-loading microfluidic chip integrated with colorimetric LAMP has been validated for the multiplex detection of gastrointestinal helminths directly from fecal samples, utilizing a passive loading mechanism that eliminates the need for external pumps [8].

The integration of sample preprocessing modules directly onto the microfluidic chip is a defining characteristic of advanced LOC systems. For example, a thin-film microfluidic system designed for Mycobacterium tuberculosis resistance genotyping incorporates chemical lysis and alcohol-free nucleic acid purification within a fully sealed, sample-to-answer platform, completing the extraction step in 18 minutes [1]. This approach minimizes user intervention and reduces the risk of contamination, a critical advantage in field settings. For aquatic species, sample matrices such as gill tissue or hemolymph from crustaceans require specialized lysis protocols to release nucleic acids from pathogens like White Spot Syndrome Virus or Infectious Hypodermal and Hematopoietic Necrosis Virus. A green and ultrafast nucleic acid extraction method utilizing sphere-mediated confinement ultrasonic grinding has been reported, achieving lysis efficiencies over 90% for common foodborne pathogens in a matter of minutes, without the use of harsh chemicals [12]. This approach is highly adaptable for on-chip integration, particularly for aquaculture POC applications.

3.2 Nucleic Acid Extraction and Purification: On-Chip Strategies

The efficiency of nucleic acid extraction is the single most important determinant of downstream assay sensitivity. Traditional column-based or organic extraction methods are ill-suited for POC deployment due to their multi-step nature and reliance on centrifugation. Microfluidic systems have therefore adopted a variety of on-chip extraction strategies. Magnetic bead-based purification is among the most widely implemented, as it allows for the capture, washing, and elution of nucleic acids through the application of external magnetic fields, eliminating the need for centrifugation. This approach has been integrated into centrifugal microfluidic discs and cartridge-based systems for the detection of Porcine Reproductive and Respiratory Syndrome Virus and Swine Influenza A Virus from oral fluid samples [18]. The protocol typically involves lysing the sample in a chaotropic buffer, binding the released nucleic acids to silica-coated magnetic beads, performing sequential wash steps to remove inhibitors, and finally eluting the purified nucleic acids in a low-ionic-strength buffer.

An alternative strategy, particularly suited for isothermal amplification platforms, is the use of direct lysis without extensive purification. The Q3 lab-on-chip real-time PCR system for Leishmania infantum detection in dogs demonstrated that non-extracted samples (NES)-including bone marrow, lymph node, and blood-could be directly loaded onto the chip and amplified, yielding overlapping quantification cycle (Cq) values compared to purified DNA [29]. This "extraction-free" approach significantly reduces assay time and complexity, though it may be more susceptible to inhibitors present in certain sample types. For environmental and food safety applications, a portable PCR system for airborne bacteria utilized simple thermal lysis of bacterial cells at 95 degrees C for 10 minutes prior to amplification, achieving limits of detection as low as 6 CFU/mL for Staphylococcus aureus [13]. The choice of extraction protocol must therefore be carefully matched to the target pathogen, sample matrix, and the tolerance of the downstream amplification chemistry to potential inhibitors.

3.3 Amplification Methodologies: PCR, LAMP, and RPA on Chip

The core of any molecular diagnostic assay is the amplification of target nucleic acid sequences. Microfluidic platforms have been engineered to accommodate a wide range of amplification chemistries, each with distinct thermal and reagent requirements.

Polymerase Chain Reaction (PCR) remains the gold standard for sensitivity and specificity. On-chip PCR systems have evolved from simple end-point detection to sophisticated real-time quantitative PCR (qPCR) platforms. A portable, battery-powered PCR thermocycler (POCT-PCR) weighing only 1.0 kg and costing US$97 has been developed for on-site detection of harmful cyanobacteria, achieving ramp rates of +1.10 degrees C/s and -1.95 degrees C/s and completing 30 cycles in 78 minutes [2]. This device utilizes custom mini-PCR tubes to enhance thermal transfer and minimize evaporation, demonstrating that robust thermal cycling can be achieved in a low-cost, handheld format. For higher throughput, on-chip qPCR using patterned silicon substrates as reaction vessels has been optimized for the detection of Staphylococcus aureus harboring the enterotoxin gene cluster, achieving quantification from 4 to 40,000 copies in 1.8 microliters of reaction mixture within 19 minutes-a significant reduction in time and volume compared to conventional 40-minute runs using 10 microliter volumes [4]. A particularly elegant innovation is the vertical microfluidic chip for solid-phase PCR (SP-PCR), which integrates all-dielectric nanostructured metasurfaces for enhanced fluorescence detection. This system utilizes a dual-heater configuration that alternates at subsecond intervals, obviating the need for active cooling and achieving a detection limit of 10 copies/reaction for multiplexed pathogen detection [15].

Loop-Mediated Isothermal Amplification (LAMP) has emerged as a dominant technology for POC applications due to its isothermal nature (typically 60-65 degrees C), high specificity, and tolerance to inhibitors. The microfluidic-RT-LAMP chip for the simultaneous detection of Porcine Epidemic Diarrhea Virus, Porcine Deltacoronavirus, and swine acute diarrhea syndrome-coronavirus achieved detection limits of 10^1 to 10^2 copies/microliter within 40 minutes, with no cross-reactivity to other common swine viruses [21]. The protocol involves loading the RNA sample into a chip pre-loaded with lyophilized LAMP reagents, followed by incubation on a simple heat block. For the detection of Avian Influenza Virus, a smartphone-based LAMP system has been validated for multiplexed detection of equine respiratory pathogens from nasal swab extracts, achieving results in approximately 30 minutes with detection limits comparable to laboratory-based PCR [22, 23]. The integration of LAMP with colorimetric detection, as demonstrated in a power-free microfluidic chip for parasitic disease detection, allows for result interpretation by the naked eye or through simple image processing, eliminating the need for expensive optical detectors [8].

Recombinase Polymerase Amplification (RPA) is another isothermal method that operates at lower temperatures (37-42 degrees C) and offers even faster amplification times (typically 15-30 minutes). The integration of RPA with CRISPR-Cas systems has been a major focus of recent research, as it combines the rapid, isothermal amplification of RPA with the sequence-specific cleavage activity of Cas enzymes. A critical challenge in this integration is the biochemical incompatibility between the trans-cleavage activity of Cas12a/Cas13a and the RPA reaction components. Five key strategies have been developed to address this: spatial isolation (using physical barriers or phase-change materials), phase separation (using density/viscosity modifiers), microfluidics (driven by centrifugal or capillary forces), crRNA design/modification, and reaction component optimization [10]. The thin-film microfluidic system for M. tuberculosis resistance genotyping successfully integrates multiplex asymmetric PCR with PAM-independent CRISPR-Cas12a detection within a fully sealed platform, achieving a limit of detection of 0.1 copies/microliter for seven clinically relevant rifampicin resistance mutations [1].

3.4 Detection Modalities and Signal Transduction

The choice of detection modality is dictated by the need for sensitivity, quantitative accuracy, and compatibility with the POC environment. Optical detection methods, including fluorescence, colorimetry, and chemiluminescence, are the most prevalent due to their simplicity and the availability of low-cost detectors.

Fluorescence-based detection is the standard for real-time PCR and LAMP. The smartphone-based LAMP platform utilizes LEDs to excite fluorescent products generated during amplification, with the smartphone camera serving as the detector. A custom software application running on the phone automatically analyzes the images to provide positive/negative determination and can populate a cloud-based database for epidemiological reporting [23]. For enhanced sensitivity, a hollow-core fiber (HCF) based optofluidic chip has been developed for immunofluorescence detection. The HCF provides an extremely high surface-to-volume ratio, shortening analyte diffusion distances and prolonging residence time, which markedly improves antibody-capture efficiency. Coaxial propagation of both light and the sample inside the HCF strengthens light-matter interaction, enabling quantitative detection of influenza A antigen within 10 minutes at a limit of detection of 2.41 pg/mL [14].

Colorimetric detection is particularly attractive for resource-limited settings as it allows for visual readout. The deep learning-enabled ratiometric signal transduction platform for Vibrio vulnificus detection converts subtle colorimetric changes from LAMP reactions into quantifiable digital outputs using a convolutional neural network (CNN). The system employs a custom-designed bottom-illumination optical module and a ratiometric analysis of the green-to-blue (G/B) channel intensity, effectively suppressing optical noise and achieving a detection limit of 10^-5 ng/microliter with a precision of 0.953 and a recall of 0.972 [3]. Similarly, the power-free microfluidic chip for parasitic detection uses chromatic analysis via image processing to interpret colorimetric LAMP results, achieving strong agreement with the gold standard method (Cohen's kappa value = 0.9) [8].

Electrochemical biosensors offer an alternative to optical methods, providing high sensitivity, low cost, and the potential for miniaturization. These platforms utilize biorecognition elements such as antibodies, aptamers, or molecularly imprinted polymers immobilized on electrode surfaces. Signal amplification strategies, including the use of nanomaterials and redox cycling, have been developed to detect antibiotic-resistant bacteria and cancer biomarkers [6, 26]. For veterinary applications, label-free detection using photonic integrated circuits (PICs) has been validated for the pen-side detection of African Swine Fever Virus and Classical Swine Fever Virus in oral fluid and serum samples, achieving sensitivities of 80.97% and 79%, respectively [17]. The PIC-based sensor detects changes in the refractive index upon binding of viral particles, eliminating the need for labeled reagents.

3.5 Multiplexing and Integrated Workflow Execution

The ability to simultaneously detect multiple pathogens is a critical requirement for syndromic surveillance and differential diagnosis. Multiplexing in microfluidic systems can be achieved through spatial separation (multiple reaction chambers), spectral encoding (using different fluorophores), or barcoding strategies. A dual-color microsphere suspension array, encoded with blue fluorescent protein and Cy5-labeled anti-Tag ssDNA, has been developed for the simultaneous detection of five respiratory pathogens, achieving a detection limit of 1 copy/microliter and a clinical sensitivity of 97% [30]. For veterinary applications, a microfluidic-RT-LAMP chip with multiple parallel channels has been designed to detect three emerging swine coronaviruses simultaneously, with coefficients of variation (CVs) less than 5% [21].

The ultimate goal of LOC technology is the "sample-to-answer" paradigm, where the entire workflow-from sample loading to result reporting-is executed automatically within a single, closed device. The iDMF-mLOCI platform (integrated digital microfluidic platform for multiplexed luminescence oxygen channeling immunoassay) exemplifies this approach for protein biomarkers. It achieves fast on-chip plasma separation (<30 s), eliminates washing cycles (100% bead retention), and provides high reproducibility (CVs < 9.1

5. Clinical Application and Performance Evaluation in Veterinary Settings

The translation of microfluidic lab-on-a-chip (LOC) platforms from engineering prototypes to clinically validated diagnostic tools in veterinary medicine represents a paradigm shift in animal healthcare delivery. Unlike human diagnostics, where centralized laboratory infrastructure is often accessible, veterinary practice-particularly in production animal systems, wildlife conservation, and companion animal emergency medicine-frequently demands diagnostic solutions that can operate in remote, resource-constrained, or biologically complex environments. The clinical performance of these platforms must therefore be evaluated not only against gold-standard reference methods but also within the operational constraints of field deployment, including rapid turnaround times, minimal sample volumes, tolerance to sample matrix variability, and robust performance across diverse host species and pathogen ecologies.

5.1 Companion Animal Diagnostics: From Hospital to Home

In small animal practice, the diagnostic imperative often centers on the rapid differentiation of infectious diseases presenting with overlapping clinical syndromes. The application of microfluidic LOC platforms to canine and feline infectious disease diagnostics has yielded particularly instructive performance data. The evaluation of a lab-on-chip real-time PCR (LOC-qPCR) system for Leishmania infantum detection in dogs, using the portable Q3-Plus V2 platform, demonstrated remarkable concordance with conventional benchtop qPCR systems [29]. This study is noteworthy for its methodological rigor: 173 DNA samples extracted from multiple tissue types-bone marrow, lymph node, blood, buffy coat, conjunctival swab, and skin-were tested alongside 93 non-extracted samples (NES). The LOC system achieved a limit of detection of less than one promastigote per milliliter, and critically, it demonstrated higher sensitivity than the reference CFX96 qPCR when testing non-extracted samples [29]. This finding is of profound clinical significance, as the ability to bypass nucleic acid extraction-a step requiring centrifuges, reagents, and technical expertise-directly addresses the major bottleneck in point-of-care molecular diagnostics. For practitioners managing canine leishmaniasis in endemic regions, the capacity to obtain a molecular-level diagnosis from a direct lymph node aspirate or buffy coat within a single clinic visit could dramatically alter treatment timelines and reduce the risk of zoonotic transmission.

The application of microfluidic isothermal amplification to equine respiratory disease diagnostics further illustrates the platform's versatility. A smartphone-integrated microfluidic LAMP system, validated against a panel of five equine respiratory pathogens, achieved detection limits comparable to laboratory-based PCR from nasal swab samples within approximately 30 minutes [22, 23]. While these initial studies focused on analytical sensitivity, the clinical validation of a LAMP microfluidic device for Streptococcus equi subsp. equi detection in guttural pouch lavage (GPL) specimens from convalescent horses provided a more rigorous assessment of real-world performance [20]. Using a triplex qPCR targeting two S. equi-specific genes (eqbE and SEQ2190) as the reference standard, the microfluidic LAMP device achieved a receiver operating characteristic area under the curve (ROC AUC) of 0.811, which was statistically indistinguishable from the benchtop LAMP assay (ROC AUC = 0.813) [20]. The ability to detect carrier horses-animals that harbor S. equi in their guttural pouches without overt clinical signs-is critical for strangles outbreak control, and this study demonstrated that the microfluidic format could identify 31 of 68 GPL specimens as positive, compared to only 12 by triplex qPCR. This apparent discordance highlights a recurring theme in veterinary LOC evaluation: the need to define the clinical gold standard carefully. The LAMP assay may detect non-viable or low-level nucleic acid that represents resolved infection or contamination, yet in the context of carrier detection, such sensitivity may actually be clinically advantageous, provided it is coupled with appropriate interpretation algorithms.

For canine enteric and respiratory pathogens, multiplexed detection remains a high priority. The development of microfluidic platforms capable of simultaneously detecting Canine Parvovirus, Canine Distemper Virus, Canine Coronavirus, and respiratory agents such as Canine Influenza A Virus and Bordetella bronchiseptica would address a significant clinical gap. The principles established in human respiratory virus panels [24, 30] are directly translatable, though the veterinary field must contend with species-specific immune responses, variable viral shedding kinetics, and the confounding presence of subclinical infections. The integration of digital microfluidic platforms for protein biomarkers, such as the iDMF-mLOCI system achieving limits of detection in the picogram per milliliter range for sepsis biomarkers like procalcitonin and interleukin-6 using only 2.2 microliters of sample [5], offers a complementary diagnostic layer. In a veterinary emergency room, the ability to simultaneously quantify a viral nucleic acid load via LOC-qPCR and a host inflammatory protein via DMF immunoassay from a single blood droplet would provide an unprecedented window into disease trajectory and prognosis.

5.2 Production Animal Diagnostics: Herd Health and Biosecurity

In swine and cattle production, where individual animal diagnostics is economically impractical, the diagnostic unit is the herd or the cohort. Microfluidic LOC platforms must therefore demonstrate not only analytical performance but also throughput, cost-effectiveness, and compatibility with pooled or pen-based sampling strategies. The evaluation of a photonic integrated circuit (PIC)-based microfluidic device for the detection of African Swine Fever Virus (ASFV) and Classical Swine Fever Virus (CSFV) directly in oral fluid and serum samples provides a landmark performance dataset [17]. The device achieved sensitivities of 80.97% and 79% for ASFV and CSFV, respectively, and specificities of 88.46% and 79.07%, using PCR as the reference method. While these values would be considered suboptimal for a confirmatory diagnostic test, the diagnostic odds ratios (DOR)-32.25 for ASFV and 14.21 for CSFV-indicate clinically meaningful discrimination. Importantly, the PIC-based approach is label-free and detects intact viral particles, which may offer advantages in detecting early infection when viral nucleic acid levels are low but virions are present in oral fluids [17]. The implications for outbreak response are substantial: a pen-side test that can reliably flag potentially infected herds within minutes, even if it requires confirmatory PCR for definitive diagnosis, can dramatically accelerate quarantine and depopulation decisions compared to the current reliance on centralized laboratory testing with its associated 24- to 72-hour turnaround.

The parallel evaluation of the same PIC-microfluidic platform for Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and Swine Influenza A Virus (SIV) in oral fluid samples revealed similar performance characteristics: sensitivity of 83.5% and specificity of 77.8% for PRRSV, and 81.8% and 82.2% for SIV, respectively [18]. The DOR values of 17.66 and 20.81, while moderate, are clinically useful in high-prevalence scenarios where rapid herd-level triage is needed. These studies underscore the importance of establishing context-specific performance thresholds for LOC devices in veterinary applications. A test with 80% sensitivity may be unacceptable for diagnosing a chronically infected individual companion animal, but for herd-level surveillance of a highly contagious pathogen, where the cost of missing a positive sample is balanced against the operational benefits of immediate on-site results, such performance may be entirely fit for purpose.

For enteric diseases in swine, a microfluidic RT-LAMP chip designed for the simultaneous detection of Porcine Epidemic Diarrhea Virus (PEDV), Porcine Deltacoronavirus (PDCoV), and Swine Acute Diarrhea Syndrome Coronavirus (SADS-CoV) demonstrated sensitivities of 92.24%, 92.19%, and 91.23%, respectively, with 100% specificity against other common swine viruses when evaluated on 173 clinical fecal samples [21]. The detection limits of 10^1 to 10^2 copies/microliter are clinically relevant, as these coronaviruses cause severe disease in neonatal piglets where even low viral loads can precipitate outbreaks. The 40-minute turnaround time and the ability to process multiple samples per chip represent a significant advance over conventional RT-qPCR, which typically requires 2-3 hours plus sample transport time [21]. For field veterinarians managing outbreaks of neonatal diarrhea-a condition with multiple viral and bacterial etiologies-the rapid etiological diagnosis provided by such a platform can guide immediate decisions on the use of autogenous vaccines, biosecurity protocols, and antimicrobial stewardship.

In bovine practice, the application of microfluidic platforms to respiratory disease diagnostics-the bovine respiratory disease (BRD) complex-remains a high priority. The development of a thin-film microfluidic system integrating sample lysis, nucleic acid purification, asymmetric PCR, and CRISPR-Cas12a detection [1] offers a template for detecting multiple BRD pathogens, including Bovine Herpesvirus 1, Bovine Viral Diarrhea Virus, Mannheimia haemolytica, and Pasteurella multocida. The ability of this system to achieve a limit of detection of 0.1 copies/microliter for drug-resistance mutations in Mycobacterium tuberculosis [1] suggests that similar sensitivity is achievable for veterinary respiratory pathogens, though the transition from human TB to bovine respiratory diagnostics requires optimization of lysis protocols for Gram-negative bacteria and the design of species-specific guide RNAs.

5.3 Aquatic Animal Health: Surveillance in Aquaculture Systems

The aquaculture sector presents uniquely demanding diagnostic environments: high-density populations, limited access to laboratory infrastructure, and the need for rapid decision-making to prevent catastrophic losses. Microfluidic LOC platforms have been evaluated for several economically devastating viral pathogens of finfish and crustaceans. The detection of Infectious Salmon Anemia Virus (ISAV) and Salmonid Alphavirus (SAV) in Atlantic salmon production would benefit enormously from on-site molecular diagnostics, given the rapidity with which these viruses spread in crowded net-pens. While direct evaluation studies in aquatic species remain less numerous than in terrestrial livestock, the performance principles established in swine and equine models are directly applicable. The integration of nucleic acid extraction via sphere-mediated confinement ultrasonic grinding [12] is particularly attractive for aquaculture, where waterborne pathogens require efficient concentration and lysis from large-volume environmental samples. This approach, achieving a lysis efficiency of over 90% and a detection limit of 7 CFU/mL in food samples [12], could be adapted for detecting White Spot Syndrome Virus or Yellow Head Virus in shrimp hemolymph or pond water, where early detection is critical for preventing total crop loss.

The evaluation of microfluidic platforms for detecting Tilapia Lake Virus (TiLV) and Koi Herpesvirus (KHV) in ornamental fish presents additional challenges, including the need for non-lethal sampling and the handling of viscous mucus or gill tissue homogenates. The centrifugal microfluidic disc system developed for integrated blood typing and hemoglobin quantification in human samples [9] offers a promising architecture for aquatic diagnostics: its ability to process 12 microliters of whole blood and complete the analytical workflow in 130 seconds using a power-independent rotational protocol [9] could be adapted for isothermal amplification of viral nucleic acids from fish blood or mucus. The deterministic cascading aliquoting architecture ensures precise metering of small volumes, which is essential when sample availability is limited (e.g., from a valuable broodstock koi or a protected amphibian species threatened by Ranaviruses In Amphibians).

5.4 Poultry and Avian Diagnostics: Flock-Level Rapid Screening

In poultry production, where individual bird testing is impractical and flock-level decisions must be made within hours, microfluidic LOC platforms offer transformative potential. The detection of Avian Influenza Virus (AIV), particularly highly pathogenic strains such as H5N1 and H7N9, is a global priority for food security and pandemic preparedness. A smartphone-integrated colorimetric microfluidic chip utilizing nanobodies specific for H7N9 AIV achieved a limit of detection of 5.9 x 10^3 EID50/0.1 mL, comparable to traditional ELISA, and was validated on real-world samples [16]. The reusability of the 3D-printed microfluidic chip-up to nine cycles without significant sensitivity loss-addresses a critical economic barrier in poultry diagnostics, where hundreds of samples may need to be screened per day [16]. The integration of smartphone-based imaging and chromatic analysis eliminates the need for a plate reader, making the platform deployable in field vaccination campaigns or emergency outbreak responses.

The power-free sample-loading microfluidic chip integrated with colorimetric LAMP for detecting gastrointestinal helminths in poultry [8] exemplifies the potential of LOC platforms to address neglected parasitic diseases. This system simultaneously detected five parasitic groups (Raillietina spp. and Ascaridia galli) with a Cohen's kappa value of 0.9 against the gold standard morphological method, indicating excellent agreement [8]. The minimum detectable DNA concentrations ranging from 4 ng to 40 pg per chip are clinically meaningful, as helminth egg shedding can be intermittent and low-level. The ability to interpret results with the naked eye-without any electronic reader-makes this platform accessible to poultry farmers in resource-limited settings, where laboratory diagnosis of helminthiasis is virtually nonexistent.

For respiratory viral diseases in poultry, the multiplex suspension array approach using magnetic microspheres encoded with fluorescent proteins [30] offers a pathway for simultaneous detection of Newcastle Disease Virus (NDV), Infectious Bronchitis Virus (IBV), Avian Metapneumovirus (aMPV), and Avian Influenza Virus (AIV). The 97% sensitivity and 90% specificity reported for human respiratory pathogens [30] suggest that comparable performance is achievable in poultry matrices (tracheal swabs, organ homogenates), though validation in chicken- or turkey-derived samples is necessary to account for matrix effects from mucins and yolk lipids.

5.5 Antimicrobial Susceptibility Testing in Veterinary Microfluidics

The crisis of antimicrobial resistance in veterinary medicine necessitates the development of rapid antimicrobial susceptibility testing (AST) platforms that can guide therapy within a single clinic visit. The egg-like multivolume microchamber-based microfluidic (EL-MVM^2) platform represents a significant advance in this regard [19]. By generating a robust antibiotic gradient across microchambers of varying volumes (12.56 to 153.86 nL) within approximately 10 minutes, this system achieved >97% predictive accuracy for susceptibility/resistance outcomes, surpassing the FDA-approval criterion for technology-based AST instruments [19]. The clinical relevance for veterinary medicine is profound: for a dairy cow with acute mastitis caused by Staphylococcus aureus or Escherichia coli, the ability to determine the minimum inhibitory concentration (MIC) for a panel of veterinary-approved antibiotics within a single milking shift could dramatically reduce the use of broad-spectrum empiric therapy and slow the emergence of resistance. The EL-MVM^2 platform's compatibility with bacterial suspensions directly from clinical specimens (milk, urine, wound exudates) without prior culture [19] addresses a critical bottleneck in traditional AST workflows.

For detection of antibiotic resistance genes directly from clinical samples, the integration of CRISPR-Cas systems with microfluidics offers sequence-specific identification of resistance determinants. The thin-film microfluidic system that achieved detection of M. tuberculosis rifampicin resistance mutations with a mutant allele frequency as low as 20% against a wild-type background [1] provides a template for detecting methicillin resistance in Staphylococcus pseudintermedius or extended-spectrum beta-lactamase (ESBL) genes in E. coli from companion animals. The dual-signal readout strategy (PCR-CRISPR) ensures sequence-level discrimination, which is essential when dealing with complex resistance phenotypes that involve multiple genetic mechanisms [1]. The challenge lies in adapting the cas12a/crRNA design to the diverse array of veterinary resistance genes and ensuring that the system can handle the mixed bacterial populations characteristic of clinical samples (e.g., polymicrobial wound infections or fecal samples).

5.6 Species-Specific Sample Matrix Challenges and Pre-Analytical Considerations

A critical yet often underappreciated aspect of clinical performance evaluation in veterinary settings is the variability of patient sample matrices. Veterinary samples differ substantially from human blood or urine in composition, viscosity, and biochemical interference. Whole blood from different species exhibits varying hematocrits, plasma protein profiles, and cellular fragility. Avian blood contains nucleated erythrocytes, which can interfere with nucleic acid extraction protocols optimized for mammalian samples. Fish mucus and skin swabs contain complex polysaccharides that inhibit PCR. Microfluidic LOC platforms must demonstrate tolerance to these matrices or incorporate onboard sample preparation modules tailored to the species of interest.

The development of microfluidic plasma separation technologies

Data Analysis, Automation, and Point-of-Care Integration

The translation of microfluidic lab-on-a-chip (LOC) technologies from research prototypes to clinically actionable veterinary diagnostic tools hinges critically upon the sophisticated integration of data analysis, automation, and point-of-care (POC) connectivity. Without robust, automated interpretation of complex biochemical signals and seamless integration into clinical workflows, even the most exquisitely sensitive microfluidic assay remains a laboratory curiosity rather than a transformative field-deployable instrument. This section dissects the architectural principles, algorithmic strategies, and integration frameworks that underpin the transition from raw microfluidic output to diagnostically meaningful, actionable results in veterinary practice.

The Paradigm Shift in Veterinary Diagnostics: From Laboratory-Centric to Algorithm-Driven POC Analysis

Traditional veterinary diagnostic workflows, as extensively reviewed by Teles and Fonseca [28], have long been constrained by a sequential paradigm: sample collection, transport to a centralized laboratory, batch processing, manual interpretation by trained personnel, and delayed result communication. This model, while reliable, is fundamentally mismatched to the temporal demands of acute clinical decision-making in livestock operations, companion animal emergencies, and aquaculture outbreak scenarios. The advent of microfluidic LOC platforms necessitates a concurrent evolution in data analysis and automation-moving beyond simple endpoint detection toward real-time, multiplexed, and self-interpreting diagnostic outputs.

The fundamental challenge lies in the inherent complexity of the signals generated by microfluidic assays. Whether these signals arise from colorimetric changes in loop-mediated isothermal amplification (LAMP) reactions, fluorescence from solid-phase PCR, electrochemical transduction from aptamer-based sensors, or optical interferometry from photonic integrated circuits (PICs), the raw data are rarely diagnostically unambiguous. As highlighted by Zhao et al. [31] in their critical evaluation of Cryptococcus detection technologies, conventional methods suffer from "subjective interpretation" and "operator-dependent variability," issues that are magnified in decentralized settings where highly trained clinical pathologists are unavailable. The solution lies in the engineering of automated, algorithmic signal transduction and decision-support systems that embed diagnostic expertise directly into the device architecture.

Automated Sample Preparation and Fluidic Control: The First Layer of Intelligent Integration

Automation in microfluidic systems begins at the front end of the analytical workflow-the extraction, purification, and metering of biological samples. The veterinary POC environment presents unique challenges compared to human clinical settings, including the handling of viscous samples (e.g., oral fluid from swine, guttural pouch lavage from equids), heterogeneous matrices (e.g., fecal material containing parasitic ova), and the requirement for rapid, hands-free operation. Tarim et al. [25] provide a comprehensive analysis of emerging microfluidic plasma separation technologies, emphasizing that effective POC devices must incorporate "rapid and low-cost plasma separation from small sample volumes" without reliance on bulky centrifugation equipment. The integration of deterministic cascading aliquoting architectures, as demonstrated by Dehghan et al. [9] in their centrifugal microfluidic disc for blood typing and hemoglobin quantification, exemplifies a critical automation principle: passive, physics-driven fluidic control eliminates the need for external pumps and trained operators, enabling a "sample-to-answer" workflow that proceeds with minimal user intervention.

A landmark study by Cheng et al. [1] illustrates the zenith of front-end automation in a veterinary-relevant context: their thin-film microfluidic system for detection of rifampicin-resistant Mycobacterium tuberculosis integrates "chemical lysis, alcohol-free nucleic acid purification, multiplex asymmetric PCR, and combined PAM-independent CRISPR-Cas12a detection within a fully sealed, sample-to-answer platform." The system completes the entire process in 78 minutes, with a detection limit of 1 CFU/mL. Crucially, the automation was achieved through microfluidic architecture rather than complex external instrumentation-a key design philosophy for POC deployment. This principle has been extended to veterinary pathogens, with Zhou et al. [21] developing a microfluidic-RT-LAMP chip for simultaneous detection of Porcine Epidemic Diarrhea Virus, Porcine Deltacoronavirus, and swine acute diarrhea syndrome-coronavirus. Their system achieved automated detection in 40 minutes with no cross-reactivity, demonstrating the scalability of integrated POC platforms for syndromic surveillance in swine herds.

Multiplex Detection and Signal Readout: The Data Acquisition Challenge

The transition from single-plex to multiplex detection is perhaps the most significant data analysis challenge in microfluidic POC diagnostics. Veterinary respiratory and enteric disease syndromes are frequently polymicrobial, requiring simultaneous discrimination of multiple viral, bacterial, and parasitic agents. Liu et al. [30] developed an elegant solution through dual-color microsphere encoding, using "blue fluorescent protein (mTagBFP) and Cy5-labeled anti-Tag ssDNA" to create a suspension array for multiplex detection of five respiratory pathogens. The system achieved "97% sensitivity and 90% specificity" in clinical testing, effectively distinguishing single and mixed infections through flow cytometric analysis. This approach illustrates a critical data analysis principle: encoding multiplexed signals onto discrete, distinguishable carriers enables algorithmic deconvolution of complex biological mixtures.

The fluorescence-based readout, however, introduces its own analytical complexities. Photobleaching, autofluorescence from biological matrices, and variability in excitation intensity can confound interpretation. Seder et al. [15] addressed these challenges through the integration of "all-dielectric nanostructured metasurfaces" beneath the PCR chamber of their vertical microfluidic chip. This nanophotonic enhancement exploits guided-mode resonance to amplify fluorescence signals, achieving a detection limit of 10 copies/reaction. The accompanying data analysis pipeline employed automated image segmentation and intensity normalization, demonstrating that hardware-level signal enhancement can simplify downstream algorithmic requirements-a critical consideration for field-deployable systems with limited computational resources.

Ratiometric, Deep Learning, and Smartphone-Enabled Analysis: The New Data Analysis Paradigm

Perhaps the most transformative advance in POC data analysis has been the integration of artificial intelligence (AI) and machine learning (ML) algorithms directly into the diagnostic workflow. Zhang et al. [3] introduced a deep learning-enabled ratiometric signal transduction strategy for colorimetric LAMP detection of Vibrio vulnificus, a zoonotic pathogen of critical importance in aquaculture environments. Their system employed a "custom-designed bottom-illumination optical module that ensures uniform signal acquisition," coupled with a convolutional neural network (CNN)-based quantification framework that converts "colorimetric biochemical reactions into robust digital outputs." The ratiometric analysis of green-to-blue (G/B) channel intensity effectively "suppresses optical noise and variability caused by fluctuating environmental illumination," a persistent challenge in field diagnostics. The deep learning model achieved "a precision of 0.953 and a recall of 0.972," with the entire assay consuming only 5 microliters of sample and delivering results within 30 minutes.

This ratiometric approach fundamentally addresses the variability inherent in colorimetric readouts. Traditional visual interpretation is subjective and susceptible to ambient lighting conditions, operator color vision, and reaction time variations. By encoding the diagnostic signal as a ratio between two wavelength channels-a technique borrowed from analytical spectroscopy-the system becomes inherently self-normalizing. The incorporation of deep learning further enhances robustness, as the CNN can learn to recognize subtle patterns in the colorimetric response that correlate with specific pathogen concentrations, even in the presence of confounding matrix effects.

The smartphone has emerged as the ideal computational platform for this new generation of AI-augmented POC diagnostics. Chen et al. [23] demonstrated an early exemplar: a "mobile platform for multiplexed detection and differentiation of disease-specific nucleic acid sequences" that employed a smartphone camera as the sensor, interfaced with a hand-held cradle containing a microfluidic chip. The system automatically analyzed fluorescent LAMP products, combined "assay information with cartridge and patient identifiers to populate a cloud-based database for epidemiological reporting." Sun et al. [22] extended this concept, developing a "smartphone-based multiplex 30-minute nucleic acid test of live virus from nasal swab extract" for equine respiratory pathogens including Equine Influenza A Virus and related agents. Their system integrated on-chip isothermal amplification with downstream smartphone-based fluorescence detection and automated cloud-based reporting.

The sophistication of smartphone-based analysis has accelerated rapidly. Das et al. [11] provide a critical overview of the integration of "coordination chemistry-driven functional molecular probes" with smartphone-assisted POC testing, noting that "artificial intelligence-machine learning-internet of things (AI-ML-IoT)-assisted data analysis" represents the future frontier of the field. They caution, however, that "device dependence, lack of standard calibration and validation methods, environmental or operational error, long-term stability, reproducibility, and biocompatibility" remain significant barriers to clinical adoption. This critique underscores a vital principle: the development of the data analysis pipeline must proceed hand-in-hand with rigorous analytical validation, including assessment of inter-device reproducibility, environmental robustness, and operator-independent performance.

Integrated Sample-to-Answer Systems: Convergence of Automation, Fluidics, and Data Analysis

The ultimate expression of LOC technology is the fully integrated sample-to-answer system, where sample introduction is the only manual step, and all subsequent processes-extraction, amplification, detection, analysis, and reporting-occur autonomously. Manessis et al. [17, 18] have pioneered this approach for transboundary swine diseases, developing a POC diagnostic device that integrates "photonic integrated circuits (PICs), microfluidics, and information and communication technology into a single platform" for detection of African Swine Fever Virus, Classical Swine Fever Virus, Porcine Reproductive and Respiratory Syndrome Virus, and Swine Influenza A Virus. Their platform employs label-free, real-time detection of viral particles through changes in the refractive index at the sensor surface, eliminating the need for enzymatic amplification or fluorescent labeling. The data analysis pipeline incorporates automated signal processing algorithms that extract diagnostic information from the PIC output, achieving sensitivities of 80-84% and specificities of 78-88% across field validation studies.

The centrifugal microfluidic platform developed by Dehghan et al. [9] exemplifies the complete integration of multiple analytical modalities. Their disc-based system performs ABO/Rh blood typing and quantitative hemoglobin analysis from 12 microliters of whole blood in 130 seconds. The data analysis component is particularly noteworthy: "a low-cost imaging module coupled with a custom image-processing algorithm provides automated, operator-independent interpretation of both agglutination patterns and colorimetric intensity." The algorithm achieved "100% sensitivity and 97.7% specificity" for agglutination detection, with hemoglobin measurements showing strong correlation (R^2 = 0.95) with a clinical CBC analyzer. This work demonstrates that careful engineering of the data analysis pipeline can enable non-specialist operators to obtain laboratory-quality results from complex microfluidic assays.

Algorithmic Integration and the Challenge of Biological Noise

A critical but often underappreciated aspect of POC data analysis is the management of biological variability and matrix interference. Veterinary samples pose unique challenges: fecal samples contain PCR inhibitors, oral fluid samples have variable viscosity and cellular content, and whole blood samples require rapid processing to prevent coagulation. The data analysis algorithms must be robust to these perturbations. Panich et al. [8] addressed this challenge in their power-free microfluidic chip for parasitic detection, integrating "chromatic analysis via image processing" that could compensate for variations in sample color and turbidity. Their system demonstrated "strong agreement with the gold standard method (Cohen's kappa value = 0.9)" for detection of gastrointestinal helminth parasites in avian fecal samples.

The integration of internal controls and normalization strategies within the data analysis pipeline is essential for robust POC performance. Latrofa et al. [29] evaluated the Q3 lab-on-chip real-time PCR system for detection of Leishmania infantum in dogs, demonstrating that "overlapping Cq values were obtained with the Q3 qPCR and CFX96 qPCR" across multiple sample types, including non-extracted samples. The system's ability to process bone marrow, lymph node, blood, and conjunctival swab samples from the same animal, with automated normalization to internal amplification controls, exemplifies best practices in POC data analysis-the algorithm must be able to distinguish true biological signal from amplification artifacts and sample-to-sample variability.

The Future of Data Analysis in Veterinary POC Diagnostics

The trajectory of data analysis in veterinary microfluidic LOC systems is clearly toward greater autonomy, deeper integration, and enhanced predictive capability. The incorporation of CRISPR-based detection systems, as reviewed by Silva et al. [7] and Liu et al. [10], introduces new data analysis challenges related to the interpretation of Cas12a/Cas13a trans-cleavage activity and the management of false-positive signals from non-specific cleavage. Liu et al. [10] systematically analyze five key strategies (spatial isolation, phase separation, microfluidics, crRNA design/modification, and reaction component optimization) for addressing the "biochemical incompatibility between trans-cleavage activity of the two Cas enzymes and RPA-based amplification" in one-tube systems. The data analysis algorithms for these systems must be capable of distinguishing true target-dependent cleavage from background noise-a challenge that demands sophisticated signal processing and statistical modeling.

Ahamed et al. [33] identify "multiplexing, integrated sample-to-answer-out design, and workflow-aligned performance benchmarks" as the critical near-term opportunities for accelerating clinical translation of POC platforms. For veterinary applications, this translates into the need for data analysis systems that can handle the unique reporting requirements of animal health surveillance-integration with national disease databases (e.g., USDA NAHMS, WOAH WAHIS), real-time geolocation tagging for outbreak mapping, and automated notification of regulatory authorities for reportable diseases.

The convergence of electrochemical biosensing with microfluidic automation, as reviewed by Kazmi et al. [6] and Khan et al. [26], offers another promising pathway. Electrochemical transduction produces quantitative, time-resolved signals that are inherently amenable to algorithmic analysis. The "AI-assisted informatics framework" proposed by Kazmi et al. [6] for integrating multimodal biomarker panels-integrating "proteomics, lipidomics, metabolomics and cytokine analysis" as described by Ghosh et al. [32] for tear fluid analysis-could be adapted for veterinary applications where multi-analyte biomarker signatures are emerging for conditions such as mastitis, sepsis, and metabolic disease.

The ultimate goal of data analysis in veterinary POC diagnostics is not merely to report a positive or negative result, but to provide actionable clinical information within the context of the individual patient, the herd, and the population. This requires algorithms that can integrate patient signalment (species, age, breed, vaccination history), geographic risk factors, and syndromic presentation with the raw diagnostic output from the microfluidic chip. The embedding of clinical decision support algorithms directly into the POC device-whether through smartphone applications, cloud-based processing, or on-chip microprocessors-represents the final frontier of integration, transforming the microfluidic LOC from a diagnostic tool into a comprehensive veterinary decision-making platform.

Challenges, Limitations, and Future Directions for Veterinary Diagnostics

The translation of microfluidic lab-on-a-chip (LOC) platforms from benchtop prototypes to routine point-of-care (POC) veterinary diagnostics is fraught with a constellation of technical, biological, and translational challenges. While the promise of rapid, decentralized, and cost-effective testing is tantalizing, the path to clinical deployment is obstructed by fundamental limitations in sample processing, assay robustness, multiplexing capacity, and regulatory alignment. This section critically dissects these barriers and delineates the future directions necessary to realize the full potential of microfluidic diagnostics in veterinary medicine.

Pre-Analytical Hurdles: The Bottleneck of Sample Preparation

The most persistent and underestimated challenge in microfluidic POC diagnostics is the integration of robust, automated sample preparation. Veterinary specimens-whole blood, feces, nasal swabs, guttural pouch lavage, oral fluids, and tissue homogenates-are notoriously complex, containing inhibitors, particulate matter, and variable pathogen loads. While microfluidic devices excel at manipulating small volumes, they are often exquisitely sensitive to fouling and clogging. The separation of plasma from whole blood, a prerequisite for many serological and molecular assays, remains a critical bottleneck. Although centrifugal microfluidics have demonstrated deterministic cascading aliquoting and passive siphon valves for plasma separation [9], and other systems have employed on-chip plasma separation in under 30 seconds [5], these solutions are often tailored to human blood and may not perform equivalently across the diverse hematocrit ranges and rheological properties of canine, feline, equine, or bovine blood. The reliance on external actuation (e.g., vacuum pumps, stepper motors) in some systems [15] undermines the "power-free" ideal of true POC devices, which is particularly critical for field deployment in remote livestock settings or wildlife conservation efforts.

Nucleic acid extraction, the cornerstone of molecular diagnostics, presents an even greater challenge. Traditional column-based or magnetic bead-based extraction is a multi-step, time-consuming process that is difficult to miniaturize without compromising yield and purity. While innovative approaches like sphere-mediated confinement ultrasonic grinding offer a "green" and ultrafast alternative [12], and fully integrated thin-film microfluidic systems have achieved automated chemical lysis and purification [1], these systems often require specialized reagents or complex fabrication. The ability to bypass extraction entirely, as demonstrated with the Q3 lab-on-chip real-time PCR for Leishmania infantum detection in canine bone marrow and lymph node samples [29], is a significant advance, but this approach is not universally applicable. For pathogens with robust cell walls (e.g., Cryptococcus spp. [31], Mycobacterium tuberculosis [1]) or those embedded in tough matrices like feces, efficient lysis without external equipment remains a formidable obstacle. The future of veterinary LOC diagnostics hinges on the development of universal, reagent-free, or minimally instrumented sample preparation modules that can handle the full spectrum of veterinary matrices with high efficiency and reproducibility.

Analytical Limitations: Sensitivity, Specificity, and the Specter of False Positives

Even when a high-quality sample is introduced, the analytical performance of microfluidic assays must meet or exceed that of gold-standard laboratory methods (e.g., real-time PCR, virus isolation) to gain clinical acceptance. A recurring theme in the literature is the trade-off between speed and sensitivity. While isothermal amplification methods like LAMP and RPA are favored for their rapid kinetics and low power requirements, they are not without significant drawbacks. The LAMP assay, in particular, is notoriously prone to false-positive results due to non-specific amplification, primer-dimer artifacts, and aerosol contamination [7, 21]. This risk is amplified in microfluidic devices where reaction volumes are small and the surface-to-volume ratio is high, potentially leading to non-specific adsorption of reagents or amplicons. The integration of CRISPR-Cas systems (e.g., Cas12a, Cas13a) with LAMP or RPA has been proposed as a "dual-signal" strategy to enhance specificity [1, 7, 10]. However, the biochemical incompatibility between the trans-cleavage activity of Cas enzymes and the amplification reaction often necessitates complex spatial isolation or phase separation strategies to achieve one-tube integration, adding to the system's complexity and cost [10].

For protein-based diagnostics, the challenges are equally acute. While digital microfluidics (DMF) platforms have achieved remarkable sensitivity (e.g., 2.2 pg/mL for IL-6 [5]), these systems often require sophisticated reagent handling, wash steps, and precise temperature control. The lateral flow assay (LFA), the current workhorse of veterinary POC testing, suffers from poor quantitative accuracy and limited sensitivity, particularly for low-abundance biomarkers [14]. The development of hollow-core fiber optofluidic chips [14] and nanophotonic-enhanced solid-phase PCR [15] represent promising attempts to break the sensitivity-speed trade-off, but their fabrication complexity and cost may limit their scalability for widespread veterinary use. Furthermore, the detection of emerging or genetically diverse pathogens, such as the myriad variants of Avian Influenza Virus or Porcine Reproductive and Respiratory Syndrome Virus, requires assays that can tolerate sequence mismatches without sacrificing specificity. The reliance on highly conserved target regions or the use of degenerate primers is a partial solution, but the rapid evolution of RNA viruses, including Infectious Salmon Anemia Virus and Salmonid Alphavirus, demands continuous assay redesign and validation.

Multiplexing and the Challenge of Differential Diagnosis

Veterinary clinicians rarely face a single pathogen; they confront syndromes (e.g., respiratory disease, neonatal diarrhea, vesicular disease) with a broad etiological differential. A microfluidic device that detects only one target is of limited clinical utility. The demand for multiplexed panels is immense, yet achieving high-order multiplexing in a microfluidic format is technically daunting. Spatial multiplexing (e.g., multiple reaction chambers or lanes) increases chip complexity and sample volume requirements [8, 23]. Spectral multiplexing (e.g., using multiple fluorophores) is limited by spectral overlap and the availability of compatible optical filters, especially in low-cost, smartphone-based readers [11, 22]. Barcoding strategies, such as the use of fluorescent protein-encoded microspheres [30], offer a promising solution for high-throughput suspension arrays, but they require flow cytometry or sophisticated imaging systems that are not yet field-deployable.

The challenge is particularly acute for aquatic species, where a single outbreak of disease in a shrimp farm or salmon net-pen could be caused by any one of a dozen viruses, including White Spot Syndrome Virus, Yellow Head Virus, Infectious Myonecrosis Virus, or Taura Syndrome Virus. A microfluidic chip that can simultaneously screen for all these agents, plus bacterial and fungal co-infections, would be transformative. However, the design of such a panel requires meticulous optimization of primer sets, amplification conditions, and detection probes to avoid cross-reactivity and ensure uniform amplification efficiency across targets [21]. The integration of internal amplification controls (IACs) is non-negotiable for validating negative results, but the inclusion of IACs further consumes precious multiplexing real estate. Future directions must focus on "universal" amplification strategies, such as metagenomic next-generation sequencing (NGS) on a chip, or the use of highly multiplexed CRISPR-Cas systems with orthogonal guide RNAs that can be activated by distinct target sequences [7]. The development of AI-driven algorithms for primer and crRNA design [7, 10] will be essential to navigate the combinatorial complexity of high-order multiplexed assays.

Biological and Clinical Context: From Pathogen Detection to Clinical Action

A fundamental limitation of current microfluidic diagnostics is their focus on pathogen detection in isolation, often divorced from the clinical context of the host. A positive PCR result for Canine Parvovirus in a fecal sample does not distinguish between a recent vaccination, a subclinical infection, or a fulminant case of hemorrhagic gastroenteritis. Similarly, the detection of Feline Coronavirus RNA does not predict the development of feline infectious peritonitis (FIP). The future of veterinary diagnostics lies in "theranostics"-the integration of diagnostic testing with prognostic and therapeutic decision-making. This requires moving beyond simple yes/no detection to quantitative viral load measurement, genotyping (e.g., distinguishing BVDV Type 1 and Type 2 or Canine Parvovirus Variants), and the detection of antimicrobial resistance markers.

The integration of antimicrobial susceptibility testing (AST) into microfluidic platforms is a critical unmet need. The egg-like multivolume microchamber (EL-MVM^2) platform [19] represents a significant step forward, enabling rapid AST by generating a gradient of antibiotic concentrations within a single chip. However, translating this concept to a panel of antibiotics relevant to veterinary medicine (e.g., for bovine mastitis or canine pyoderma) and validating it against clinical breakpoints established by organizations like the Clinical and Laboratory Standards Institute (CLSI) is a monumental task. Furthermore, the detection of host biomarkers of inflammation (e.g., serum amyloid A, haptoglobin, procalcitonin) alongside pathogen nucleic acids could provide a more holistic picture of disease severity and prognosis [5, 32]. The integration of multi-omic data (proteomics, metabolomics, transcriptomics) from a single microfluidic sample, as envisioned for human dry eye disease [32], is a distant but aspirational goal for veterinary medicine.

Regulatory, Manufacturing, and Sustainability Challenges

The path from a published prototype to a commercially available, regulatory-cleared veterinary diagnostic is arduous and expensive. The veterinary diagnostic market is fragmented across species (companion animal, livestock, poultry, aquaculture, wildlife) and geographic regions, each with its own regulatory framework (e.g., USDA, WOAH, EMA). The validation requirements for a POC test are stringent, requiring large-scale clinical trials across multiple sites to demonstrate sensitivity, specificity, and reproducibility against a reference standard [17, 18]. The photonic integrated circuit (PIC)-based devices for African Swine Fever Virus and Classical Swine Fever Virus [17], and for PRRSV and Swine Influenza A Virus [18], have undergone rigorous validation, but their sensitivities (80-83%) and specificities (77-88%) are still below the 95% threshold often demanded by clinicians for critical disease management decisions. The lack of standardized reference materials for many veterinary pathogens, particularly for aquatic viruses like Decapod Iridescent Virus 1 or Macrobrachium rosenbergii Nodavirus, further complicates validation.

Manufacturing scalability and cost are equally critical. Many microfluidic devices are fabricated using complex, low-throughput processes (e.g., photolithography, soft lithography) in cleanroom facilities, making them prohibitively expensive for single-use veterinary applications. The shift toward injection-molded thermoplastics, 3D-printed chips [16], and paper-based microfluidics [27] is a positive trend, but these materials must be compatible with the biochemical assays and provide adequate optical clarity for detection. The environmental impact of single-use plastic cartridges is a growing concern, particularly in low- and middle-income countries where waste management infrastructure is weak [35]. The development of biodegradable or recyclable materials for microfluidic devices, as advocated by Ongaro et al. [35], is an urgent priority. Furthermore, the reliance on lyophilized reagents that require cold-chain storage remains a significant logistical barrier for field deployment in tropical or remote environments. The development of thermally stable, ambient-temperature-stable reagents is a key area for future innovation.

Future Directions: Toward a Truly Integrated and Intelligent Diagnostic Ecosystem

The future of microfluidic veterinary diagnostics lies in the convergence of several transformative technologies. First, the integration of artificial intelligence (AI) and machine learning (ML) will be paramount. Deep learning algorithms can already convert subtle colorimetric changes in LAMP assays into robust digital outputs, improving sensitivity and objectivity [3]. AI can also be used for automated image analysis of agglutination patterns [9], for optimizing assay design [7, 10], and for interpreting complex multiplexed data. The integration of smartphone-based detection with cloud-based data analytics [11, 22, 23] creates a powerful ecosystem for real-time disease surveillance, enabling veterinarians, producers, and public health authorities to track outbreaks at a local, regional, or national level. This is particularly critical for notifiable diseases like Foot-and-Mouth Disease Virus, Avian Influenza Virus, and Rabies Lyssavirus, where rapid reporting is essential for containment.

Second, the development of "sample-to-answer" systems that require minimal user intervention will be crucial for adoption by non-laboratory personnel (e.g., farmers, veterinary technicians, wildlife rangers). The thin-film microfluidic system for tuberculosis resistance genotyping [1] and the iDMF-mLOCI platform for sepsis biomarkers [5] exemplify this paradigm, but they must be further simplified and ruggedized. The use of power-free sample loading mechanisms, such as capillary action or vacuum-driven flow [8, 15], and the integration of all necessary reagents in a pre-loaded, sealed cartridge are essential design principles.

Third, the expansion of microfluidic diagnostics into non-traditional veterinary sectors, such as aquaculture and wildlife conservation, offers immense opportunities. The development of portable PCR devices for on-site detection of harmful cyanobacteria [2] and airborne bacteria [13] demonstrates the versatility of the technology. For aquaculture, microfluidic chips could be deployed on boats or at hatcheries for the rapid screening of broodstock, fry, and water samples for pathogens like Viral Hemorrhagic Septicemia Virus, Infectious Hematopoietic Necrosis Virus, and Koi Herpesvirus. For wildlife, handheld devices could be used for the non-invasive detection of pathogens in fecal or environmental samples, aiding in the conservation of endangered species threatened by diseases like Ranaviruses In Amphibians or Canine Distemper Virus In Wildlife.

Finally, the field must embrace a "systems-level" approach to validation and regulation. This includes the establishment of biobanks of well-characterized veterinary samples, the development of international reference standards for emerging pathogens, and the creation of regulatory pathways that are agile enough to accommodate rapid technological innovation while ensuring patient and animal safety. The integration of alternative assays within lifecycle-based regulatory frameworks, as proposed for veterinary vaccine quality control [34], could serve as a model for the validation of microfluidic diagnostics. By addressing these challenges head-on, the veterinary community can harness the full power of microfluidics to transform animal health, enhance food security, and safeguard public health.

References

1. [1] Cheng J, Li X, Wang S, Zhang W, Chen J, Sui G, et al.. A sample-to-answer thin-film microfluidic system integrating multiplex asymmetric PCR and CRISPR for rapid detection of Mycobacterium Tuberculosis drug-resistance mutations . Sensors and Actuators B: Chemical. 2026. DOI: https://doi.org/10.1016/j.snb.2026.139901

2. [2] Mahardika I, Huh E, Seo Y, Kin S, Chun S, Lee S, et al.. A low-cost, battery-powered PCR thermocycler with enhanced thermal stability for on-site detection of harmful cyanobacteria. Talanta Open. 2026. DOI: https://doi.org/10.1016/j.talo.2026.100644

3. [3] Zhang H, Tsai M, Chen J. Deep learning-enabled ratiometric signal transduction for portable and intelligent colorimetric LAMP biosensing of Vibrio vulnificus . Analytical Biochemistry. 2026. DOI: https://doi.org/10.1016/j.ab.2026.116136

4. [4] Pereira A, Schoonderwoerd S, Wiederkehr R, Chieffi D, Fusco V, Marson G. A sensitive and compact on-site and real time quantitative detection of foodborne and clinical pathogens by on-chip qPCR. Talanta Open. 2026. DOI: https://doi.org/10.1016/j.talo.2026.100633

5. [5] Li Z, Zhang H, Guo Q, Wang Y, Mao E, Zhao B, et al.. Minimalist digital microfluidics for high-performance multiplexed protein POCT: A wash-free, sample-to-answer, and trace-sample paradigm . Biosensors and Bioelectronics. 2026. DOI: https://doi.org/10.1016/j.bios.2026.118585

6. [6] Kazmi I, Alzarea S, Shahwan M, Thakur P, Rathore V, Hajarnavis A, et al.. Electrochemical biosensors for MLKL-related necroptosis biomarkers in lung cancer: From bench to clinical laboratory . Clinica Chimica Acta. 2026. DOI: https://doi.org/10.1016/j.cca.2026.121022

7. [7] Silva C, Nascimento G, Cruz P, Arancibia R, Andrade Belitardo E, Castro T, et al.. Design principles for LAMP-CRISPR molecular diagnostics. Methods. 2026. DOI: https://doi.org/10.1016/j.ymeth.2026.03.014

8. [8] Panich W, Puttharugsa C, Tejangkura T, Chontananarth T. A power-free sample-loading microfluidic chip integrated with a colorimetric loop-mediated isothermal amplification and a chromatic analysis via image processing for multiplex detection of parasitic diseases . Analytica Chimica Acta. 2026. DOI: https://doi.org/10.1016/j.aca.2026.345419

9. [9] Dehghan A, Jobani B, Malekpour R, Kiani M, Eghbal M, Pishbin E, et al.. Integrated microfluidic platform for simultaneous blood typing and hemoglobin quantification at the point of care. Results in Engineering. 2026. DOI: https://doi.org/10.1016/j.rineng.2026.109923

10. [10] Liu J, Chen Y, Kang H, Wu H, Luo J, Wang P, et al.. Integrating CRISPR-Cas12a/Cas13a and recombinase polymerase amplification in one tube for point-of-care testing: practices and innovations . Microchemical Journal. 2026. DOI: https://doi.org/10.1016/j.microc.2026.117962

11. [11] Das R, Bej S, Ghosh M, Banerjee P. From solution to digitized screen: Chemical engineering perspectives on functional molecular probes with smartphone-assisted point-of-care testing (POCT) devices: A functional mastery or a conceptual myth? . Chemical Engineering Journal. 2026. DOI: https://doi.org/10.1016/j.cej.2026.176007

12. [12] Jia K, Yang F, Yuan J, Yan L, Wang L, Li Y, et al.. Green and ultrafast nucleic acid extraction via sphere-mediated confinement ultrasonic grinding for sensitive foodborne pathogen detection. Ultrasonics Sonochemistry. 2026. DOI: https://doi.org/10.1016/j.ultsonch.2026.107868

13. [13] Lee J, Jeong Y, Choi S, Shin D, Nam H, Yoon T, et al.. Development of a portable real-time PCR system for on-site detection of airborne bacteria. Sensors and Actuators Reports. 2026. DOI: https://doi.org/10.1016/j.snr.2026.100470

14. [14] Ren X, Wen T, Liu Y, Liu X, Lin F, Dong Z, et al.. A hollow-core fiber based optofluidic chip for rapid immunofluorescence detection with simultaneous enhancement of sensitivity and enrichment efficiency.. In Analysis. 2026. DOI: https://doi.org/10.1039/d5an01308a

15. [15] Seder I, Beliaev L, Tellez RC, Anthon C, Grissa D, Zheng T, et al.. Point-of-Care Solid-Phase PCR in a Vertical Microfluidic Chip Integrated with All-Dielectric Nanostructured Metasurface for Highly Sensitive, Multiplexed Pathogen Detection.. ACS Sensors. 2025. DOI: https://doi.org/10.1021/acssensors.5c02435

16. [16] Ji Y, Li F, Qu Z, Wang X, Cui P, Deng G, et al.. Combining nanobody generation platform, 3D-printed microfluidic chip, and smartphone detection system for monitoring emerging virus-caused diseases.. Biosensors & bioelectronics. 2025. DOI: https://doi.org/10.1016/j.bios.2025.117972

17. [17] Manessis G, Frant M, Podgorska K, Gal-Cison A, Lyjak M, Urbaniak K, et al.. Label-Free Detection of African Swine Fever and Classical Swine Fever in the Point-of-Care Setting Using Photonic Integrated Circuits Integrated in a Microfluidic Device. Pathogens. 2024. DOI: https://doi.org/10.3390/pathogens13050415

18. [18] Manessis G, Frant M, Wozniakowski G, Nannucci L, Benedetti M, Denes L, et al.. Point-of-Care and Label-Free Detection of Porcine Reproductive and Respiratory Syndrome and Swine Influenza Viruses Using a Microfluidic Device with Photonic Integrated Circuits. Viruses. 2022. DOI: https://doi.org/10.3390/v14050988

19. [19] Azizi M, Nguyen AV, Dogan B, Zhang S, Simpson K, Abbaspourrad A. Antimicrobial Susceptibility Testing in a Rapid Single Test via an Egg-like Multivolume Microchamber-Based Microfluidic Platform.. ACS Applied Materials and Interfaces. 2021. DOI: https://doi.org/10.1021/acsami.0c23096

20. [20] Boyle A, Rankin S, O'Shea K, Stefanovski D, Peng J, Song J, et al.. Detection of Streptococcus equi subsp. equi in guttural pouch lavage samples using a loop-mediated isothermal nucleic acid amplification microfluidic device. Journal of Veterinary Internal Medicine. 2021. DOI: https://doi.org/10.1111/jvim.16105

21. [21] Zhou L, Chen Y, Fang X, Liu Y, Du M, Lu X, et al.. Microfluidic-RT-LAMP chip for the point-of-care detection of emerging and re-emerging enteric coronaviruses in swine. Analytica Chimica Acta. 2020. DOI: https://doi.org/10.1016/j.aca.2020.05.034

22. [22] Sun F, Ganguli A, Nguyen J, Brisbin R, Shanmugam K, Hirschberg D, et al.. Smartphone-based multiplex 30-minute nucleic acid test of live virus from nasal swab extract.. Lab on a Chip. 2020. DOI: https://doi.org/10.1039/d0lc00304b

23. [23] Chen W, Yu H, Sun F, Ornob A, Brisbin R, Ganguli A, et al.. Mobile Platform for Multiplexed Detection and Differentiation of Disease-Specific Nucleic Acid Sequences, Using Microfluidic Loop-Mediated Isothermal Amplification and Smartphone Detection.. Analytical Chemistry. 2017. DOI: https://doi.org/10.1021/acs.analchem.7b02478

24. [24] Hatem H, Mysara M, Ramadan R. Trends of nucleic acid - based point-of-care diagnostics for infectious diseases. Journal of Biological Engineering. 2026. DOI: https://doi.org/10.1186/s13036-026-00681-6

25. [25] Tarim EA, Mauk M, El-Tholoth M. Emerging Microfluidic Plasma Separation Technologies for Point-of-Care Diagnostics: Moving Beyond Conventional Centrifugation. Biosensors. 2025. DOI: https://doi.org/10.3390/bios16010014

26. [26] Khan MU, Rahman M, Zahan N, Masud M, Sarker S, Haque MH. Electrochemical Biosensing for Antibiotic-Resistant Bacteria: Advances, Challenges, and Future Directions. Micromachines. 2025. DOI: https://doi.org/10.3390/mi16090986

27. [27] Mao K, Min X, Zhang H, Zhang K, Cao H, Guo Y, et al.. Paper-based microfluidics for rapid diagnostics and drug delivery.. Journal of Controlled Release. 2020. DOI: https://doi.org/10.1016/j.jconrel.2020.03.010

28. [28] Teles F, Fonseca L. Nucleic-Acid Testing, New Platforms and Nanotechnology for Point-of-Decision Diagnosis of Animal Pathogens. Methods in molecular biology. 2014. DOI: https://doi.org/10.1007/978-1-4939-2004-4_20

29. [29] Latrofa MS, Cereda M, Louzada-Flores VN, Dantas-Torres F, Otranto D. Q3 lab-on-chip real-time PCR for the diagnosis of Leishmania infantum infection in dogs. Journal of Clinical Microbiology. 2024. DOI: https://doi.org/10.1128/jcm.00104-24

30. [30] Liu X, Cheng L, Zheng B, Hu S, Wei S, Hu Y. Dual color microsphere encoded by fluorescent protein and Cy5-labeled anti-Tag ssDNA for multiplex detection of respiratory pathogens . Talanta. 2026. DOI: https://doi.org/10.1016/j.talanta.2026.129909

31. [31] Zhao Z, Zhang S, Huang Y, Zhao E, Zhou Y, Liu J, et al.. Cryptococcus detection technologies: An overview of conventional, immunological, and molecular methods, and future development directions . Talanta. 2026. DOI: https://doi.org/10.1016/j.talanta.2026.129883

32. [32] Ghosh S, Sahoo J, Singh K. Tear fluid multi-omics and biosensor integration for diagnosis and personalized therapeutics in dry eye disease . Experimental Eye Research. 2026. DOI: https://doi.org/10.1016/j.exer.2026.111004

33. [33] Ahamed M, Guo B, Khalid M, Pal T, Guo F, Guan W. Point-of-care testing for early diagnosis and population screening of Alzheimer's disease: Recent advances and perspectives . Nano Today. 2026. DOI: https://doi.org/10.1016/j.nantod.2026.103033

34. [34] Abousenna M. Reframing veterinary vaccine quality control: Integrating alternative assays within lifecycle-based regulatory frameworks . Veterinary Immunology and Immunopathology. 2026. DOI: https://doi.org/10.1016/j.vetimm.2026.111109

35. [35] Ongaro A, Ndlovu Z, Sollier E, Otieno C, Ondoa P, Street A, et al.. Engineering a sustainable future for point-of-care diagnostics and single-use microfluidic devices. Lab on a Chip. 2022. DOI: https://doi.org/10.1039/d2lc00380e