Dynamic Range in Digital PCR

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-27

Quick Answer

• Dynamic range in digital PCR is governed by the number of partitions analyzed and the probability that each partition contains at least one target copy.
• Select a partition count and sample dilution so that the expected target concentration falls within the quantifiable window, typically between 0.1 and 5 copies per partition.
• The upper limit of quantification is constrained by partition saturation, and exceeding this limit produces inaccurate copy-number estimates that require dilution and reanalysis.

At a Glance

Understanding Digital PCR Dynamic Range

Digital PCR partitions a single reaction into thousands of independent micro-reactions. Each partition either contains a target sequence or does not. After amplification, the instrument counts positive and negative partitions. The proportion of negative partitions follows the Poisson distribution, which allows the calculation of the original target concentration without a standard curve.

The dynamic range is the span of target concentrations that can be measured accurately in a single experiment. It is bounded by two limits. At the lower end, the detection limit is set by the total number of partitions examined. At the upper end, the saturation limit is set by the probability that a partition contains more than one target copy.

The relationship between the number of partitions and the measurable concentration range is direct. A system with more partitions can detect lower concentrations because the probability of observing at least one positive partition increases with the number of independent reactions. A system with more partitions can also measure higher concentrations because the fraction of negative partitions remains measurable at higher target loads.

The Poisson correction is the mathematical foundation of this calculation. When the average number of target copies per partition is known, the fraction of negative partitions is equal to e raised to the negative of that average. The instrument measures the fraction of negative partitions and solves for the average copy number. This calculation is valid only when the target molecules are distributed randomly across partitions, which requires that the sample is mixed thoroughly and that the template does not aggregate.

The practical consequence is that the dynamic range is not a fixed property of the instrument alone. It depends on the number of partitions, the total reaction volume, the sample dilution, and the quality of the template. A laboratory can extend the dynamic range by choosing a system with more partitions, by adjusting the dilution, or by running multiple dilutions in parallel.

Partition Count and the Quantifiable Window

The number of partitions is the primary determinant of the dynamic range. Each partition is an independent measurement event. The instrument classifies each partition as positive or negative, and the total number of partitions sets the statistical power of the experiment.

For a given target concentration, the fraction of positive partitions is determined by the average copies per partition. If the average is 0.5 copies per partition, then approximately 39 percent of partitions will be negative and 61 percent will be positive. If the average is 1 copy per partition, then 37 percent will be negative and 63 percent will be positive. If the average is 5 copies per partition, then only 0.7 percent of partitions will be negative.

The dynamic range is therefore limited by the ability to distinguish a small number of positive partitions from zero and a small number of negative partitions from zero. At the lower limit, the instrument must detect a single positive partition among thousands of negatives. At the upper limit, the instrument must detect a single negative partition among thousands of positives.

The number of partitions determines the precision of the measurement at both extremes. With 20,000 partitions, the lower limit of detection is approximately 1 target molecule in the total reaction volume. With 100,000 partitions, the lower limit improves to approximately 1 target molecule in a volume five times larger. The upper limit is similarly affected. With 20,000 partitions, the highest measurable concentration is approximately 5 copies per partition. With 100,000 partitions, the highest measurable concentration is approximately 5 copies per partition as well, but the total number of target molecules that can be quantified is larger because the total volume is larger.

The choice of partition count is a tradeoff between the dynamic range and the cost of the consumable. Higher partition counts require more reagents, more imaging time, and more data storage. The laboratory must balance the need for a wide dynamic range against the cost of the experiment.

Poisson Statistics and the Saturation Limit

The Poisson distribution describes the probability of observing a given number of target molecules in a partition when the average number of molecules per partition is known. The key assumption is that the target molecules are distributed independently and randomly across the partitions.

The fraction of negative partitions is the probability that a partition contains zero target molecules. This fraction is equal to the exponential of the negative average copies per partition. The instrument measures the fraction of negative partitions and solves for the average copies per partition.

The accuracy of this calculation depends on the fraction of negative partitions remaining above zero. When the average copies per partition exceeds 5, the fraction of negative partitions falls below 0.7 percent. For a system with 20,000 partitions, this means fewer than 140 negative partitions are expected. The statistical uncertainty in counting such a small number of negatives becomes large, and the calculated concentration becomes unreliable.

The saturation limit is the concentration at which the fraction of negative partitions is too small to be measured with acceptable precision. This limit is approximately 5 copies per partition for most digital PCR systems. Above this concentration, the instrument reports a concentration that is biased toward the lower end of the true value because the number of negative partitions is underestimated.

The lower limit of detection is similarly constrained. When the average copies per partition is below 0.01, the fraction of positive partitions is approximately 1 percent. For a system with 20,000 partitions, this means approximately 200 positive partitions are expected. The measurement is possible but the relative uncertainty is high because the number of positive partitions is small.

The optimal range for quantification is between 0.1 and 1.6 copies per partition. In this range, the fraction of positive partitions is between 9.5 percent and 80 percent, and the Poisson calculation is most accurate. The relative error is minimized because the number of positive and negative partitions is balanced.

Dilution Factors and the Practical Dynamic Range

The dilution factor is the laboratory control that brings the target concentration into the quantifiable window. The sample is diluted so that the expected average copies per partition falls within the optimal range of 0.1 to 1.6.

The dilution factor is calculated from the expected concentration of the target in the original sample. If the expected concentration is 100,000 copies per microliter and the reaction volume is 20 microliters, the total number of target molecules is 2 million. To achieve an average of 1 copy per partition in a 20,000-partition system, the total number of target molecules must be 20,000. The required dilution factor is 100.

The calculation is straightforward, but the practical execution requires careful pipetting. Serial dilutions are used to achieve the target dilution factor. Each dilution step introduces a pipetting error of approximately 1 to 2 percent. A 10-fold serial dilution performed in three steps has a cumulative error of approximately 3 to 6 percent. This error is propagated into the final concentration estimate.

The laboratory should verify the dilution factor by measuring the concentration of the diluted sample with an independent method. Spectrophotometry or fluorometry can be used to measure the nucleic acid concentration before the digital PCR reaction. The measured concentration should be within 10 percent of the expected concentration. If the measured concentration deviates by more than 10 percent, the dilution should be repeated.

The choice of dilution factor also affects the number of target molecules that are available for the reaction. A high dilution factor reduces the number of target molecules in the reaction, which increases the relative error. A low dilution factor increases the number of target molecules but may push the concentration above the saturation limit. The optimal dilution factor is the one that places the target concentration in the middle of the quantifiable window.

Partition Volume and the Absolute Quantification

The partition volume determines the absolute number of target molecules that can be measured. Each partition contains a fixed volume of the reaction mixture. The number of target molecules in a partition is the product of the target concentration and the partition volume.

The partition volume is set by the instrument and the consumable. Some systems use partitions of 1 nanoliter, while others use partitions of 0.5 nanoliters or less. The total reaction volume is the product of the partition volume and the number of partitions.

The dynamic range is expressed in terms of copies per partition, but the absolute concentration is expressed in copies per microliter. The conversion between the two is the partition volume. A concentration of 1 copy per partition in a 1-nanoliter partition is equivalent to 1,000 copies per microliter. The same concentration in a 0.5-nanoliter partition is equivalent to 2,000 copies per microliter.

The choice of partition volume affects the dynamic range in absolute terms. A system with smaller partitions can measure higher absolute concentrations because the same number of copies per partition is concentrated in a smaller volume. A system with larger partitions can measure lower absolute concentrations because the same number of copies per partition is diluted in a larger volume.

The laboratory must consider the partition volume when selecting the dilution factor. The target concentration in the original sample is expressed in copies per microliter. The dilution factor must be adjusted to account for the partition volume so that the final concentration in the reaction mixture produces the desired copies per partition.

Template Quality and Its Effect on Dynamic Range

The dynamic range of a digital PCR assay is valid only when the template is intact and free of inhibitors. Degraded template produces a lower effective concentration because the target sequence is no longer present in every molecule. Inhibitors reduce the efficiency of the amplification reaction, which can cause false-negative partitions.

The quality of the template is assessed before the digital PCR reaction. The concentration of the nucleic acid is measured by spectrophotometry or fluorophore. The purity is assessed by the ratio of absorbance at 260 and 280 nanometers for DNA and at 260 and 230 nanometers for RNA. The integrity is assessed by gel electrophoresis or microfluidic analysis.

The template quality affects the dynamic range in two ways. First, degraded template reduces the number of amplifiable target molecules. The measured concentration is lower than the true concentration because some target molecules are fragmented and cannot be amplified. Second, inhibitors reduce the efficiency of the amplification. The fraction of positive partitions is lower than expected, which produces a concentration estimate that is biased downward.

The laboratory should verify the template quality before the digital PCR reaction. The concentration should be measured with a method that is specific to the target sequence, such as a quantitative PCR assay. The amplification efficiency should be verified with a dilution series. If the amplification efficiency is below 90 percent, the template should be purified or the assay should be redesigned.

The template quality also affects the reproducibility of the assay. A template that is partially degraded produces variable results between replicates because the degradation is not uniform. The laboratory should run at least three replicates of each sample to assess the variability. The coefficient of variation should be below 15 percent for a reliable measurement.

Controls and the Interpretation of Results

The interpretation of digital PCR results requires the use of appropriate controls. The controls are used to verify the performance of the assay and to identify the sources of error.

The no-template control is a reaction that contains all of the reagents except the template. This control is used to detect contamination of the reagents or the environment. The no-template control should produce no positive partitions. If the no-template control produces positive partitions, the assay is contaminated and the results are invalid.

The positive control is a reaction that contains a known concentration of the target. This control is used to verify the performance of the assay. The positive control should produce a concentration that is within the expected range. If the positive control produces a concentration that is outside the expected range, the assay is not performing correctly.

The negative control is a reaction that contains a template that is known to be negative for the target. This control is used to verify the specificity of the assay. The negative control should produce no positive partitions. If the negative control produces positive partitions, the assay is not specific and the results are invalid.

The no-amplification control is a reaction that contains the template but no polymerase. This control is used to detect the presence of the target that is not amplified. The no-amplification control should produce no positive partitions. If the no-amplification control produces positive partitions, the target is present in the template but is not being amplified, which indicates a problem with the assay.

The interpretation of the digital PCR results is based on the comparison of the sample to the controls. The sample concentration is calculated from the fraction of positive partitions. The concentration is reported with a confidence interval that is based on the number of partitions and the number of positive partitions.

The MIQE Guidelines and the Reporting of Digital PCR Results

The Minimum Information for Publication of Quantitative Real-Time PCR Experiments guidelines provide a framework for the reporting of qPCR experiments. These guidelines are also relevant to digital PCR because they address the transparency and the reproducibility of the measurements.

The MIQE guidelines require the reporting of the experimental conditions, the reagents, the instrumentation, and the analysis methods. The guidelines require the reporting of the number of partitions, the partition volume, the target concentration, and the confidence interval. The guidelines require the reporting of the controls and the results of the controls.

The MIQE guidelines are published in Clinical Chemistry and are available online. The guidelines are intended to improve the reproducibility of the quantitative PCR experiments by ensuring that the methods are described in sufficient detail. The guidelines are also intended to improve the interpretation of the results by ensuring that the limitations of the assay are reported.

The laboratory should follow the MIQE guidelines when reporting the digital PCR results. The report should include the number of partitions, the partition volume, the target concentration, the confidence interval, and the controls. The report should also include the dilution factor, the template quality, and the amplification efficiency.

The MIQE guidelines are a useful reference for the design of the digital PCR experiments. The guidelines provide a checklist of the information that should be reported. The guidelines also provide a framework for the interpretation of the results.

The NIST Role in the Measurement Science

The National Institute of Standards and Technology provides the measurement science that supports the digital PCR. The NIST develops the standard reference materials and the calibration methods that are used to verify the performance of the digital PCR instruments.

The NIST laboratories are involved in the development of the measurement methods for the nucleic acid quantification. The NIST provides the reference materials for the DNA and the RNA quantification. The NIST also provides the calibration methods for the digital PCR instruments.

The NIST reference materials are used to verify the accuracy of the digital PCR measurements. The reference materials are characterized by the NIST using the multiple methods. The reference materials are used to calibrate the digital PCR instruments and to verify the performance of the assay.

The NIST also provides the guidance for the quality control of the digital PCR measurements. The guidance includes the use of the reference materials, the calibration methods, and the statistical analysis. The guidance is intended to improve the reliability of the digital PCR measurements.

The laboratory should use the NIST reference materials when available. The reference materials provide a traceable standard for the digital PCR measurements. The reference materials are used to verify the accuracy of the measurements and to identify the sources of the error.

Biosafety and the Institutional Oversight

The digital PCR experiments involve the use of the nucleic acid and the amplification of the target sequences. The experiments are subject to the biosafety regulations and the institutional oversight.

The biosafety principles are described in the Biosafety in Microbiological and Biomedical Laboratories, which is published by the CDC and the NIH. The guidelines provide the risk assessment and the containment requirements for the work with the biological agents. The guidelines also provide the requirements for the institutional oversight.

The NIH Guidelines for the Recombinant or Synthetic Nucleic Acid Molecules provide the oversight for the work with the recombinant or the synthetic nucleic acid. The guidelines require the institutional review of the experiments and the approval of the protocols. The guidelines also require the training of the personnel and the documentation of the experiments.

The laboratory should follow the biosafety principles and the institutional oversight requirements. The laboratory should conduct a risk assessment of the experiments and the containment requirements. The laboratory should also follow the institutional requirements for the training and the oversight.

The digital PCR experiments are typically performed in a biosafety level 1 or 2 laboratory. The experiments involve the amplification of the nucleic acid, which is a low-risk procedure. The laboratory should follow the standard practices for the handling of the nucleic acid and the amplification products.

Practical Implementation Steps

The following steps are a practical guide for the implementation of the digital PCR assay with the appropriate dynamic range.

1. Determine the expected concentration of the target in the sample. Use the literature or the previous experiments to estimate the concentration.
2. Choose the digital PCR system and the consumable. The system should have a sufficient number of partitions to cover the expected concentration range.
3. Calculate the dilution factor that is required to bring the target concentration into the quantifiable window. The target concentration should be between 0.1 and 1.6 copies per partition.
4. Prepare the serial dilutions of the sample. Use the calibrated pipettes and the verified the dilution steps.
5. Measure the concentration of the diluted sample with an independent method. The concentration should be within 10 percent of the expected value.
6. Set up the digital PCR reaction with the appropriate controls. The controls include the no-template control, the positive control, and the negative control.
7. Run the digital PCR reaction and collect the data. The instrument should report the number of positive and negative partitions.
8. Analyze the data and calculate the target concentration. The concentration should be reported with the confidence interval.
9. Verify the results with the controls. The no-template control should be negative, the positive control should be within the expected range, and the negative control should be negative.
10. Report the results according to the MIQE guidelines. The report should include the number of partitions, the partition volume, the target concentration, the confidence interval, and the controls.

Records and Measurements

The laboratory should maintain the records of the digital PCR experiments. The records should include the following information:

• The date of the experiment and the operator
• The sample identification and the source
• The expected concentration of the target
• The dilution factor and the dilution steps
• The concentration of the diluted sample
• The digital PCR system and the consumable
• The number of partitions and the partition volume
• The number of positive and negative partitions
• The target concentration and the confidence interval
• The results of the controls
• The amplification efficiency and the template quality

The records should be maintained in a laboratory notebook or an electronic system. The records should be reviewed by the laboratory supervisor. The records should be available for the audit and the inspection.

Common Failure Patterns

The following are the common failure patterns in the digital PCR and the troubleshooting steps.

Limitations and the Professional Escalation

The digital PCR has several limitations that should be considered when interpreting the results.

The dynamic range is limited by the number of partitions and the saturation limit. The dynamic range can be extended by the dilution, but the dilution introduces the error. The dynamic range is also limited by the template quality and the amplification efficiency.

The digital PCR is a relative measurement. The concentration is calculated from the fraction of positive partitions, which is based on the Poisson distribution. The Poisson distribution assumes that the target molecules are distributed randomly. If the target molecules are not distributed randomly, the concentration estimate is biased.

The digital PCR is also limited by the cost and the complexity. The digital PCR systems are more expensive than the qPCR systems. The digital PCR also requires more time and the expertise to perform.

The laboratory should escalate the results to the supervisor if the results are unexpected or if the controls fail. The escalation should include the description of the problem, the data, and the recommended action. The supervisor should review the results and determine the appropriate action.

A Decision Framework for Matching Partition Count and Dilution to the Target Range

Selecting the correct partition count and dilution factor is the central operational decision in digital PCR. The existing guidance describes the mathematical boundaries of the quantifiable window, but laboratories still face a practical problem when a sample's concentration is unknown or spans several orders of magnitude. A structured decision framework converts the Poisson statistics into a repeatable workflow that can be applied before reagents are committed. This section provides a tiered decision process, a record system for dilution verification, and a troubleshooting method for the most common failure mode, which is the mismatch between the expected and the actual target concentration.

Tier 1: Define the Expected Concentration Range

The first decision is not about the instrument. It is about the sample. The laboratory must define the expected concentration range of the target before choosing the partition count or the dilution factor. This range can come from prior measurements, published literature for the same sample type, or a preliminary quantification with an independent method such as quantitative PCR or fluorometric nucleic acid measurement. The expected range should be expressed as a lower bound and an upper bound in copies per microliter of the undiluted sample.

The width of this expected range determines the number of dilution levels that must be prepared. If the expected range spans less than one order of magnitude, a single dilution level may be sufficient. If the expected range spans two or more orders of magnitude, the laboratory should prepare multiple dilution levels in parallel. The goal is to ensure that at least one dilution level produces a concentration between 0.1 and 1.6 copies per partition, which is the optimal quantification window described in the earlier sections.

The expected range also determines whether the partition count of the available instrument is adequate. A system with 20,000 partitions can quantify a maximum of approximately 5 copies per partition before saturation. If the undiluted sample is expected to contain 100,000 copies per microliter and the partition volume is 1 nanoliter, the undiluted sample would produce 100 copies per partition, which is far above the saturation limit. The laboratory must dilute the sample by at least 100-fold to bring the concentration into the quantifiable window. If the expected range is so wide that a single dilution cannot cover both the lower and the upper bounds, the laboratory must either run multiple dilutions or select a system with a higher partition count.

Tier 2: Calculate the Required Dilution Factor

The dilution factor is calculated from the expected concentration, the partition volume, and the target copies per partition. The formula is the expected concentration in copies per microliter multiplied by the partition volume in microliters to give the expected copies per partition. The dilution factor is then the ratio of this value to the desired copies per partition, which should be between 0.1 and 1.6.

For example, if the expected concentration is 50,000 copies per microliter and the partition volume is 1 nanoliter, the expected copies per partition is 50. To achieve 1 copy per partition, the dilution factor is 50. To achieve 0.5 copies per partition, the dilution factor is 100. The laboratory should choose a dilution factor that places the expected concentration near the middle of the quantifiable window, which is approximately 0.5 to 1 copy per partition. This choice provides the greatest margin for error in both directions.

The dilution factor should be implemented as a serial dilution instead of a single large dilution step. A single 100-fold dilution is difficult to perform accurately because it requires a very small volume of the sample. A serial dilution of 10-fold followed by 10-fold is more accurate because each step uses a larger volume. The cumulative error of a two-step 10-fold serial dilution is approximately 2 to 4 percent, which is acceptable for most digital PCR applications. The laboratory should verify the dilution factor by measuring the concentration of the diluted sample with an independent method before loading the reaction.

Tier 3: Select the Partition Count Based on the Lower Detection Limit

The partition count determines the lower limit of detection. The lower limit is the concentration at which the probability of observing at least one positive partition is acceptably high. For a system with 20,000 partitions, the lower limit of detection is approximately 1 target molecule in the total reaction volume. For a system with 100,000 partitions, the lower limit is approximately 1 target molecule in a volume five times larger.

The laboratory should select the partition count based on the lower bound of the expected concentration range. If the lower bound is 10 copies per microliter and the reaction volume is 20 microliters, the total number of target molecules is 200. A system with 20,000 partitions would be sufficient because the expected number of positive partitions is 200, which is well above the detection limit. If the lower bound is 1 copy per microliter, the total number of target molecules is 20, and a system with 20,000 partitions would be marginal because the expected number of positive partitions is only 20. A system with 100,000 partitions would provide a more reliable measurement.

The partition count also affects the upper limit of quantification. The upper limit is approximately 5 copies per partition for all systems, but the total number of target molecules that can be quantified is the product of the partition count and the copies per partition. A system with 100,000 partitions can quantify up to 500,000 target molecules in a single reaction, while a system with 20,000 partitions can quantify up to 100,000 target molecules. The laboratory should select the partition count that provides sufficient capacity for the expected concentration range.

Tier 4: Prepare Multiple Dilution Levels for Unknown Samples

When the expected concentration range is uncertain, the laboratory should prepare multiple dilution levels in parallel. This approach is the most robust way to ensure that at least one dilution level falls within the quantifiable window. The dilution levels should be spaced by 10-fold increments. For example, if the undiluted sample is expected to contain between 1,000 and 1,000,000 copies per microliter, the laboratory should prepare dilutions of 10-fold, 100-fold, and 1,000-fold.

Each dilution level is loaded into a separate digital PCR reaction. The results from the dilution levels that fall within the quantifiable window are used to calculate the concentration. The results from the dilution levels that are above the saturation limit or below the detection limit are discarded. The concentration calculated from the dilution levels that fall within the quantifiable window should agree with each other within the expected error. If the calculated concentrations from two dilution levels differ by more than 20 percent, the dilution or the template quality should be investigated.

The use of multiple dilution levels increases the cost of the experiment because each dilution level requires a separate reaction. The laboratory should balance the cost of the additional reactions against the risk of an inaccurate result. For a sample with a well-characterized concentration, a single dilution level is sufficient. For a sample with an unknown concentration, multiple dilution levels are the safest approach.

Records and Measurements for the Dilution Decision

The laboratory should record the following information for each dilution decision:

• The expected concentration range and the source of the estimate
• The chosen dilution factor and the serial dilution steps
• The measured concentration of the diluted sample and the method used
• The partition count and the partition volume of the instrument
• The expected copies per partition for each dilution level
• The number of positive and negative partitions for each dilution level
• The calculated concentration and the confidence interval for each dilution level

These records should be maintained in the laboratory notebook or the electronic system. The records should be reviewed by the laboratory supervisor before the results are reported. The records should be available for audit and inspection.

Common Failure Pattern: The Dilution Mismatch

The most common failure pattern in the dilution decision is the mismatch between the expected and the actual concentration. This mismatch produces either all-positive partitions or all-negative partitions. The troubleshooting steps are described in the Common Failure Patterns table in the earlier section, but the decision framework provides a more systematic approach.

If all partitions are positive, the actual concentration is higher than the expected concentration. The laboratory should prepare a higher dilution factor and repeat the analysis. The new dilution factor should be at least 10-fold higher than the original. If all partitions are negative, the actual concentration is lower than the expected concentration. The laboratory should prepare a lower dilution factor or use a system with a higher partition count.

The laboratory should also verify the template quality when the dilution mismatch occurs. A degraded template can produce a lower effective concentration than expected, which can cause all-negative partitions. An inhibitor can reduce the amplification efficiency, which can cause false-negative partitions. The template quality should be assessed before the dilution is repeated.

Welfare and Safety Context

The dilution and the loading of the digital PCR reactions involve the handling of nucleic acid and the use of the amplification reagents. The laboratory should follow the biosafety principles described in the Biosafety in Microbiological and Biomedical Laboratories, which is published by the CDC and the NIH. The laboratory should conduct a risk assessment of the experiments and the containment requirements. The laboratory should also follow the institutional requirements for the training and the oversight.

The NIH Guidelines for the Recombinant or Synthetic Nucleic Acid Molecules provide the oversight for the work with the recombinant or the synthetic nucleic acid. The laboratory should follow the institutional requirements for the review and the approval of the protocols. The laboratory should also follow the standard practices for the handling of the nucleic acid and the amplification products.

Professional Escalation Criteria

The laboratory should escalate the results to the supervisor if the dilution mismatch cannot be resolved by the troubleshooting steps. The escalation should include the description of the problem, the data, and the recommended action. The supervisor should review the results and determine the appropriate action.

The escalation is also required if the measured concentration of the diluted sample deviates from the expected concentration by more than 10 percent. This deviation indicates a problem with the dilution or the measurement method. The supervisor should review the dilution steps and the measurement method to identify the source of the error.

The escalation is also required if the concentration from the multiple dilution levels differs by more than 20 percent. This difference indicates a problem with the template quality or the dilution accuracy. The supervisor should review the template quality and the dilution steps to identify the source of the error.

Frequently Asked Questions

How many partitions are needed to detect a target at a concentration of 1 copy per microliter?

The number of partitions required depends on the total reaction volume. If the reaction volume is 20 microliters, the total number of target molecules is 20. To detect 20 target molecules with a high probability, the number of partitions should be at least 20,000. With 20,000 partitions, the expected number of positive partitions is 20, which is sufficient for a reliable measurement.

What is the maximum concentration that can be quantified in a single digital PCR reaction?

The maximum concentration is approximately 5 copies per partition. Above this concentration, the fraction of negative partitions is too small to be measured with confidence. For a system with 20,000 partitions and a partition volume of 1 nanoliter, the maximum concentration is approximately 5,000 copies per microliter.

How does the number of partitions affect the dynamic range?

The number of partitions determines the lower limit of detection and the upper limit of quantification. A higher number of partitions allows the detection of lower concentrations because the probability of observing at least one positive partition increases. A higher number of partitions also allows the measurement of higher concentrations because the fraction of negative partitions remains measurable at higher target concentrations.

What is the optimal concentration of the target in the digital PCR reaction?

The optimal concentration is between 0.1 and 1.6 copies per partition. In this range, the fraction of positive partitions is between 9.5 percent and 80 percent. The Poisson error is minimized, and the measurement is most accurate.

How do I choose the dilution factor for my sample?

The dilution factor is chosen to bring the target concentration into the optimal range of 0.1 to 1.6 copies per partition. The dilution factor is calculated by dividing the expected concentration by the target concentration. The dilution factor should be verified by measuring the concentration of the diluted sample with an independent method.

What is the difference between the digital PCR and the qPCR?

The digital PCR is an absolute quantification method that does not require a standard curve. The qPCR is a relative quantification method that requires a standard curve. The digital PCR is more precise and more sensitive than the qPCR, but it is also more expensive and more complex.

How do I verify the accuracy of the digital PCR measurement?

The accuracy of the digital PCR measurement is verified by using the reference materials and the controls. The reference materials are provided by the NIST and are traceable to the primary standards. The controls include the no-template control, the positive control, and the negative control.

What are the common sources of error in the digital PCR?

The common sources of error include the pipetting error, the template degradation, the amplification inhibition, and the contamination. The pipetting error is introduced during the dilution steps. The template degradation reduces the effective concentration. The amplification inhibition reduces the fraction of positive partitions. The contamination produces false-positive results.

Related Molecular Biology Guides

• Annealing Temperature vs Melting Temperature in PCR
• Aerosol Contamination in PCR: Causes and Prevention
• How to Find Annealing Temperature for PCR: A Practical Guide
• Mycoplasma Contamination PCR: Detection and Prevention
• PCR Reaction: Principles, Steps, and Applications

References and Further Reading

• Molecular Biology and Laboratory Methods. National Library of Medicine.
• Biosafety in Microbiological and Biomedical Laboratories. CDC and NIH.
• NIH Guidelines for Recombinant or Synthetic Nucleic Acid Molecules. National Institutes of Health.
• Addgene Protocols. Addgene.
• MIQE Guidelines. Clinical Chemistry.
• NIST Laboratory Programs. National Institute of Standards and Technology.
• Fluorescence-coded logarithmic-dilution digital droplet PCR for ultrawide-dynamic-range nucleic acid quantification.. Biosensors & bioelectronics, 2023.
• Highly accurate and sensitive absolute quantification of bacterial strains in human fecal samples.. Microbiome, 2024.
• Digital PCR modeling for maximal sensitivity, dynamic range and measurement precision.. PloS one, 2015.
• Immuno-PCR with digital readout.. Biochemical and biophysical research communications, 2017.
• Reverse transcription-free digital-quantitative-PCR for microRNA analysis.. The Analyst, 2023.

This article is educational and does not replace validated laboratory procedures, institutional biosafety review, manufacturer instructions, or professional interpretation.