PCR Additives for Inhibitor Tolerance

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

Quick Answer

Bovine serum albumin (BSA) and other PCR additives improve amplification from inhibitor-contaminated templates by sequestering inhibitory compounds or stabilizing polymerase activity.
Select an additive based on inhibitor type, polymerase compatibility, and detection chemistry, then validate with spike-in controls before routine use.
No single additive removes all inhibition, and excessive concentrations can suppress PCR, so titration and inhibition controls are mandatory.

At a Glance

Additive	Primary Mechanism	Typical Working Range	Best Compatibility	Key Limitation
Bovine serum albumin (BSA)	Binds inhibitory compounds such as phenolic substances, humic acids, and heme, stabilizes polymerase	0.1 to 1.0 mg/mL in the final reaction	Standard Taq and proofreading polymerases, qPCR with careful lot testing	Can interfere with fluorescent probes at high concentrations, lot-to-lot variability
Betaine	Reduces GC base-pair stacking and equalizes melting temperatures	0.5 to 1.5 M final concentration	GC-rich templates, standard and proofreading polymerases	High concentrations can inhibit polymerase and alter annealing specificity
Dimethyl sulfoxide (DMSO)	Disrupts hydrogen bonding and reduces secondary structure	1% to 10% v/v final concentration	Standard Taq polymerases, less suited to proofreading enzymes	Inhibits polymerase activity at higher concentrations, may reduce yield
Formamide	Lowers melting temperature and destabilizes secondary structure	1% to 5% v/v final concentration	Standard Taq polymerases, useful for GC-rich templates	Can inhibit polymerase and interfere with fluorescent detection
T4 gene 32 protein	Binds single-stranded DNA and improves polymerase processivity	0.1 to 0.5 µg per 50 µL reaction	Polymerases with lower processivity, difficult templates	May interfere with downstream cloning or sequencing if not removed
Nonionic detergents (Triton X-100, Tween 20)	Stabilize polymerase and reduce aggregation	0.1% to 1% v/v final concentration	Most polymerases, often included in commercial buffers	Limited effect on strong inhibitors such as humic acids

Understanding PCR Inhibition and Additive Function

PCR inhibition occurs when a substance in the sample reduces amplification efficiency, delays the threshold cycle, or completely suppresses product formation. Inhibitors act through several mechanisms. Some bind directly to the DNA polymerase and block its active site. Others chelate magnesium ions that the polymerase requires for catalytic activity. Some inhibitors interact with the template DNA itself, preventing primer annealing or extension. A fourth group interferes with the fluorescent detection system in quantitative PCR, which produces false-negative or inaccurate results even when amplification occurs.

Common inhibitors in biological samples include heme and its derivatives in blood, humic and fulvic acids in soil and plant material, melanin in skin and hair samples, bile salts in feces, urea in urine, and polysaccharides in food samples. Environmental samples frequently contain humic acids that are structurally similar to DNA and can copurify with nucleic acids. Forensic samples often contain heme and other blood components. Clinical samples can contain heparin, which is a strong inhibitor of DNA polymerase.

The practical consequence is that a researcher may obtain no amplification, weak amplification, or inconsistent results from a sample that contains adequate DNA. The problem is not the absence of template but the presence of an interfering substance. Additives are one class of solutions to this problem. They are distinct from DNA purification methods, which remove inhibitors before amplification, and from polymerase formulations that are engineered to tolerate inhibitors.

Why Additives Are Used

Additives are used when purification is incomplete, when the sample is too small to permit additional purification, or when the purification method itself introduces an inhibitor. In forensic and clinical settings, samples are often limited and cannot be re-collected. In environmental microbiology, the sample matrix is complex and purification may not remove all inhibitors. In those cases, an additive can be added directly to the PCR reaction to improve the chance of successful amplification.

Additives are also used to improve amplification of difficult templates, such as GC-rich sequences that form secondary structures. This is a separate function from inhibitor tolerance, but the same additive can serve both purposes. For example, DMSO and betaine are used for GC-rich templates because they reduce secondary structure, and they also have some effect on inhibitor tolerance.

How Additives Work

The mechanisms of PCR additives fall into several categories. Some additives bind to the inhibitor directly, preventing it from interacting with the polymerase or the DNA. BSA is the most common example. It binds to phenolic compounds, fatty acids, and heme, and it can also stabilize the polymerase by coating the surface of the reaction tube. Other additives, such as DMSO and glycerol, alter the chemical environment of the reaction. They reduce the melting temperature of DNA, which can help primers anneal to templates that have strong secondary structure. They also change the activity of the polymerase, sometimes increasing processivity and sometimes reducing it.

Some additives are proteins that interact with the polymerase itself. T4 gene 32 protein binds to single-stranded DNA and can increase the processivity of the polymerase. This is useful when the template is long or when the polymerase has low processivity. Other additives are detergents that stabilize the polymerase and prevent it from denaturing at the high temperatures used in PCR.

The choice of additive depends on the inhibitor type, the polymerase type, the template sequence, and the detection chemistry. There is no universal additive. A researcher must test the additive in the specific reaction system and with the specific sample type.

Practical Workflow for Selecting an Additive

Step 1: Identify the Inhibitor

The first decision is to determine what is inhibiting the reaction. This is not always possible, but it is the most useful information. If the sample is blood, the inhibitor is likely heme or hematocrit. If the sample is soil, the inhibitor is likely humic acid. If the sample is a food product, the inhibitor may be a polysaccharide or a dye. If the sample is a clinical specimen, the inhibitor may be heparin or another anticoagulant.

The identification can be done by testing the sample with a known positive control. If the positive control amplifies without the sample but fails with the sample, the sample contains an inhibitor. If the positive control fails even without the sample, the problem is in the reaction components, not the sample.

Step 2: Choose the Additive

The choice of additive depends on the inhibitor type and the polymerase. BSA is the first choice for many researchers because it is inexpensive, easy to use, and effective against a wide range of inhibitors. It is particularly effective against heme, fatty acids, and phenolic compounds. DMSO is a second choice for GC-rich templates and for reactions that need a lower melting temperature. It is less effective against heme and humic acids.

T7 gene 32 protein is useful for long templates and for polymerases with low processivity. It is not a general inhibitor-tolerance additive. Glycerol is used to stabilize the polymerase and to reduce the melting temperature. It is not a strong inhibitor-tolerance agent.

Step 3: Test the Additive in a Controlled Experiment

The additive must be tested in the specific reaction system. The test should include a positive control without the additive, a positive control with the additive, a negative control without the template, and the test sample with and without the additive. The concentration of the additive should be tested in a range, because the optimal concentration depends on the polymerase, the buffer, and the template.

The test should be done with the same polymerase, buffer, and thermal cycling conditions that will be used in the actual experiment. The result should be evaluated by the amplification curve, the threshold cycle, and the product yield. The additive should not be used if it reduces the amplification of the positive control.

Step 4: Validate with a Spike-In Control

A spike-in control is a known amount of a control template that is added to the sample. The control template should be a different sequence from the target, and it should be amplified with a different primer pair. The spike-in control is used to determine whether the sample inhibits the reaction. If the spike-in control amplifies with the same efficiency in the sample as in the positive control, the sample is not inhibitory. If the spike-in control is delayed or absent, the sample is inhibitory.

The spike-in control is also used to determine whether the additive restores amplification. If the spike-in control amplifies with the additive but not without it, the additive is effective. The spike-in control should be used in every experiment that involves a new sample type or a new additive.

Step 5: Record and Report

The concentration of the additive, the lot number, the manufacturer, and the reaction conditions should be recorded. The threshold cycle and the amplification efficiency should be recorded for each condition. The results should be reported in the methods section of any publication, and the additive should be described in enough detail that another researcher can reproduce the experiment.

Common Failure Patterns and Troubleshooting

Failure Pattern 1: No Amplification with the Additive

If the additive does not restore amplification, the first step is to check the concentration. A concentration that is too high can inhibit the polymerase. A concentration that is too low may not be sufficient to bind the inhibitor. The concentration should be tested in a range, and the positive control should be used to determine the optimal concentration.

The second step is to check the polymerase. Some polymerases are more sensitive to additives than others. A polymerase that is engineered for inhibitor tolerance may not need an additive, and the additive may actually reduce its activity. The polymerase should be tested with and without the additive.

The third step is to check the buffer. Some buffers contain components that interact with the additive. For example, a buffer that contains a high concentration of salt may reduce the effectiveness of BSA. The buffer should be tested with and without the additive.

Failure Pattern 2: Amplification Is Delayed

A delayed threshold cycle indicates that the reaction is inhibited but not completely suppressed. The additive may be partially effective. The concentration of the additive should be increased, or a different additive should be tested. The delay can also be caused by a low template concentration, which is not an inhibitor problem.

Failure Pattern 3: Amplification Is Nonspecific

Nonspecific amplification can be caused by an additive that reduces the annealing temperature too much. DMSO and glycerol can reduce the melting temperature of the primers, which can lead to nonspecific binding. The annealing temperature should be adjusted, or the additive concentration should be reduced.

Failure Pattern 4: The Additive Interferes with the Detection System

Some additives interfere with the fluorescent dyes used in qPCR. BSA can bind to some dyes, and DMSO can quench fluorescence. The additive should be tested with the same detection chemistry that will be used in the experiment. If the additive interferes with the detection, a different additive should be used.

Compatibility with Polymerase Types

Standard Taq Polymerase

Standard Taq polymerase is the most common polymerase used in PCR. It is a thermostable DNA polymerase that is isolated from Thermus aquaticus. It is relatively tolerant to additives, and it is the most common polymerase used with BSA, DMSO, and glycerol. The optimal concentration of the additive should be tested for each batch of Taq polymerase.

Proofreading Polymerases

Proofreading polymerases have 3' to 5' exonuclease activity, which allows them to correct errors during DNA synthesis. They are used for cloning and for high-fidelity amplification. They are more sensitive to additives than standard Taq polymerase. DMSO can reduce the proofreading activity, and BSA can interfere with the enzyme. The additive should be tested with the specific proofreading polymerase, and the concentration should be lower than that used with Taq.

Hot-Start Polymerases

Hot-start polymerases are modified to be inactive at room temperature and active at high temperature. They are used to reduce nonspecific amplification. They are generally compatible with BSA and DMSO, but the additive should be tested with the specific hot-start polymerase. The additive should not be added before the hot-start activation step, because it can interfere with the activation.

Reverse Transcriptases

Reverse transcriptases are used in reverse transcription PCR to convert RNA to DNA. They are more sensitive to inhibitors than DNA polymerases. BSA can be used to stabilize the reverse transcriptase, but the concentration should be tested. The reverse transcription step should be performed with the additive, and the cDNA should be amplified with the same additive.

High-Fidelity Polymerases

High-fidelity polymerases are a class of proofreading polymerases that have a low error rate. They are used for cloning and sequencing. They are sensitive to additives, and the additive should be tested with the specific high-fidelity polymerase. DMSO can reduce the fidelity of the polymerase, and BSA can interfere with the enzyme.

Compatibility with Detection Chemistry

SYBR Green

SYBR Green is a dye that binds to double-stranded DNA and fluoresces. It is used in PCR to detect the amplification product. BSA can bind to SYBR Green and reduce the fluorescence. The concentration of BSA should be tested with the SYBR Green, and the dye should be used at the recommended concentration.

TaqMan Probes

TaqMan probes are used in PCR to detect a specific sequence. The probe is a short DNA sequence that is labeled with a fluorescent dye and a quencher. The additive can interfere with the probe, and the probe should be tested with the additive. BSA can bind to the probe, and DMSO can quench the fluorescence.

Digital PCR

Digital PCR is a method that partitions the sample into many small reactions. The additive can be used in digital PCR, but the concentration should be tested. The additive can affect the partitioning, and the detection should be tested with the additive.

Practical Implementation Steps

Step 1: Prepare a Stock Solution

The additive should be prepared as a stock solution. The stock solution should be filtered and stored at the recommended temperature. The stock solution should be tested for contamination before use.

Step 2: Prepare the Reaction

The reaction should be prepared with the additive at the recommended concentration. The additive should be added to the reaction before the polymerase. The reaction should be mixed and centrifuged.

Step 3: Run the PCR

The PCR should be run with the recommended thermal cycling conditions. The additive can affect the melting temperature, so the annealing temperature should be adjusted. The annealing temperature should be tested with the additive.

Step 4: Analyze the Results

The results should be analyzed by the amplification curve, the threshold cycle, and the product yield. The additive should be evaluated by the positive control and the spike-in control.

Records and Measurements

Records to Keep

The following records should be kept for each PCR run:

The additive name, lot number, and concentration
The polymerase name, lot number, and concentration
The buffer name and concentration
The template name and concentration
The thermal cycling conditions
The threshold cycle and the amplification curve
The positive control and the spike-in control results

Measurements to Make

The following measurements should be made for each PCR run:

The threshold cycle for the positive control
The threshold cycle for the sample
The threshold cycle for the spike-in control
The amplification efficiency
The product yield

Quality Controls

The following quality controls should be used for each PCR run:

A positive control without the additive
A positive control with the additive
A negative control without the template
A spike-in control with the sample

Common Failure Patterns

Failure Pattern 1: The Additive Does Not Work

The additive does not work if the sample is inhibited and the additive does not restore amplification. The cause is usually a concentration that is too low or a mismatch between the additive and the inhibitor. The solution is to test a range of concentrations and to test a different additive.

Failure Pattern 2: The Additive Inhibits the PCR

The additive inhibits the PCR if the positive control does not amplify with the additive. The cause is usually a concentration that is too high. The solution is to reduce the concentration or to use a different additive.

Failure Pattern 3: The Additive Interferes with the Detection

The additive interferes with the detection if the fluorescence is reduced or the threshold is delayed. The cause is usually an interaction between the additive and the dye or the probe. The solution is to test the additive with the detection chemistry and to use a different additive.

Failure Pattern 4: The Additive Is Not Reproducible

The additive is not reproducible if the results vary between runs. The cause is usually a variation in the additive concentration or a variation in the sample. The solution is to prepare the additive fresh and to use the same batch.

Safety and Regulatory Context

Biosafety

Recombinant DNA

The use of PCR additives is not regulated by the NIH Guidelines for Recombinant or Synthetic Nucleic Acid Molecules. The guidelines apply to the use of recombinant or synthetic nucleic acid molecules, not to the additives. The researcher should follow the guidelines for the use of the nucleic acid molecules.

Laboratory Standards

The laboratory should follow the standards for the use of the reagents. The standards include the use of the appropriate controls, the use of the appropriate equipment, and the use of the appropriate procedures. The laboratory should also follow the standards for the use of the equipment.

Professional Escalation Criteria

When to Escalate

The researcher should escalate the problem if the additive does not work, if the additive inhibits the PCR, or if the additive is not reproducible. The escalation should be to a supervisor or a laboratory manager.

What to Report

The researcher should report the following information:

The additive name and concentration
The sample name and concentration
The polymerase name and concentration
The buffer name and concentration
The thermal cycling conditions
The results of the positive control and the spike-in control

What to Expect

The supervisor or laboratory manager should review the information and recommend a different additive or a different concentration. The supervisor should also review the sample preparation and the purification method.

Building a Decision Matrix for Additive Selection Based on Inhibitor Class and Sample Matrix

A practical decision matrix translates inhibitor identification into a defensible additive choice. The matrix approach differs from a simple lookup table because it forces the researcher to score the sample matrix, the suspected inhibitor class, the polymerase type, and the detection chemistry before committing to an additive. This structured comparison reduces the trial-and-error burden and produces records that another researcher can interpret.

Constructing the Matrix

The matrix should be built as a table with the sample matrix on one axis and the candidate additives on the other. Each cell contains a suitability score based on published mechanisms and documented use patterns. The score is not a substitute for empirical testing, but it narrows the candidate list before you spend reagents and thermal cycler time.

The first axis is the sample matrix. Blood, soil, feces, plant tissue, forensic swabs, and food homogenates each carry characteristic inhibitors. Blood introduces heme, hematocrit, and immunoglobulins. Soil and plant material introduce humic and fulvic acids. Feces introduce bile salts and complex polysaccharides. Forensic samples often combine blood components with environmental contaminants. Food samples may contain dyes, polysaccharides, and phenolic preservatives.

The second axis is the additive. BSA, DMSO, betaine, formamide, T4 gene 32 protein, and nonionic detergents are the common candidates. Each has a documented mechanism and a known compatibility profile with polymerase types and detection chemistries.

The matrix cell contains a score from one to three. A score of one means the additive has a documented mechanism against the inhibitor class but requires validation. A score of two means the additive has a documented mechanism and published compatibility with the polymerase type. A score of three means the additive has a documented mechanism, published compatibility, and a low risk of interfering with the detection chemistry.

Scoring the Matrix

For blood samples, BSA scores three because it binds heme and stabilizes the polymerase. DMSO scores one because it does not bind heme and may reduce polymerase activity. Betaine scores one because it addresses GC content, not heme. Formamide scores one for the same reason. T4 gene 32 protein scores two because it improves processivity but does not bind heme. Nonionic detergents score two because they stabilize the polymerase but do not remove heme.

For soil samples, BSA scores three because it binds humic acids. DMSO scores one because it does not bind humic acids. Betaine scores one. Formamide scores one. T4 gene 32 protein scores two because it can improve amplification from partially purified soil DNA. Nonionic detergents score one because they have limited effect on humic acids.

For fecal samples, BSA scores two because it binds bile salts but may not fully neutralize polysaccharides. DMSO scores one. Betaine scores one. Formamide scores one. T4 gene 32 protein scores two. Nonionic detergents score two because they can help with polysaccharide-related inhibition.

For forensic blood samples, BSA scores three. DMSO scores one. Betaine scores one. Formamide scores one. T4 gene 32 protein scores two. Nonionic detergents score two.

For food samples, the score depends on the specific inhibitor. If the inhibitor is a polysaccharide, nonionic detergents score two and BSA scores one. If the inhibitor is a phenolic preservative, BSA scores three and the others score one.

Using the Matrix in Practice

The matrix is a starting point, not a substitute for a spike-in control. The researcher should select the highest-scoring additive for the sample matrix, then test it in a controlled experiment. The experiment should include a positive control without the additive, a positive control with the additive, a negative control, and the sample with and without the additive. The spike-in control should be included to measure the amplification efficiency.

The matrix should be updated with the results of each experiment. If the additive restores amplification, the score remains. If the additive does not restore amplification, the score should be reduced and the next candidate tested. This iterative process builds a local matrix that is specific to the laboratory, the polymerase, and the sample type.

Matrix Limitations

The matrix does not replace empirical testing. The matrix is a decision aid that reduces the number of additives to test. The matrix does not account for lot-to-lot variability in the additive or the polymerase. The matrix does not account for the concentration of the inhibitor, which can vary widely between samples. The matrix should be updated as new data are collected.

The matrix also does not account for the detection chemistry. BSA can interfere with some fluorescent dyes, and DMSO can quench fluorescence. The matrix should include a separate column for detection chemistry compatibility, or the researcher should test the additive with the detection chemistry before running the full experiment.

A Record System for Additive Validation

A structured record system is necessary for reproducible additive use. The record system should capture the additive, the sample, the polymerase, the detection chemistry, and the results. The record system should be designed so that another researcher can reproduce the experiment without additional information.

The Additive Record

The additive record should include the additive name, the manufacturer, the catalog number, the lot number, the stock concentration, the final concentration, and the preparation date. The lot number is important because BSA and other protein additives can vary between lots. The preparation date is important because some additives degrade over time.

The additive record should also include the solvent used to prepare the stock solution. BSA is often prepared in water or in a buffer. DMSO is often prepared as a pure liquid. The solvent can affect the additive activity and the compatibility with the polymerase.

The Sample Record

The sample record should include the sample type, the collection date, the storage condition, the extraction method, and the DNA concentration. The sample type is important because different matrices contain different inhibitors. The extraction method is important because some extraction methods remove inhibitors more effectively than others.

The sample record should also include the dilution factor. Dilution is a common strategy for reducing inhibitor concentration, but it also reduces the template concentration. The dilution factor should be recorded so that the effect of the additive can be separated from the effect of the dilution.

The Reaction Record

The reaction record should include the polymerase name, the manufacturer, the catalog number, the lot number, the buffer name, the magnesium concentration, the primer concentration, the template concentration, and the additive concentration. The reaction record should also include the thermal cycling conditions, including the denaturation temperature, the annealing temperature, the extension temperature, and the number of cycles.

The reaction record should include the detection chemistry. If the reaction uses SYBR Green, the dye concentration should be recorded. If the reaction uses a TaqMan probe, the probe sequence and concentration should be recorded. The detection chemistry affects the compatibility with the additive.

The Result Record

The result record should include the threshold cycle for the positive control, the threshold cycle for the sample, the threshold cycle for the spike-in control, and the amplification efficiency. The result record should also include the product yield, which can be measured by gel electrophoresis or by a fluorometric assay.

The result record should include a qualitative assessment of the amplification curve. A normal amplification curve has a clear exponential phase and a plateau. A delayed amplification curve has a higher threshold cycle. A suppressed amplification curve has no amplification. The qualitative assessment helps to identify the failure pattern.

The Decision Record

The decision record should include the additive selected, the concentration tested, the result, and the next step. The decision record should be updated after each experiment. The decision record should be used to update the decision matrix.

The decision record should include the reason for the decision. The reason should be based on the matrix score, the published evidence, or the previous experimental results. The reason should be recorded so that the decision can be reviewed.

A Troubleshooting Method for Additive Failure

When an additive fails to restore amplification, the failure should be investigated systematically. The troubleshooting method should separate the additive problem from the sample problem, the polymerase problem, and the detection problem.

Step 1: Confirm the Positive Control

The first step is to confirm that the positive control amplifies without the additive. If the positive control does not amplify, the problem is in the reaction components, not the additive. The polymerase, the buffer, the dNTPs, and the primers should be checked. The thermal cycler should be checked for correct temperature and timing.

Step 2: Confirm the Positive Control with the Additive

The second step is to confirm that the positive control amplifies with the additive. If the positive control does not amplify with the additive, the additive is inhibiting the reaction. The concentration should be reduced, or a different additive should be tested.

Step 3: Confirm the Sample without the Additive

The third step is to confirm that the sample does not amplify without the additive. If the sample amplifies without the additive, the additive is not needed. If the sample does not amplify without the additive, the sample is inhibited.

Step 4: Confirm the Sample with the Additive

The fourth step is to confirm that the sample amplifies with the additive. If the sample amplifies with the additive, the additive is effective. If the sample does not amplify with the additive, the additive is not effective against the inhibitor.

Step 5: Test a Range of Additive Concentrations

The fifth step is to test a range of additive concentrations. The concentration should be tested from the recommended concentration to a higher concentration. The concentration should be tested with the positive control and the sample. The optimal concentration is the one that restores amplification without reducing the positive control.

Step 6: Test a Different Additive

The sixth step is to test a different additive. The matrix should be used to select the next additive. The new additive should be tested with the positive control and the sample.

Step 7: Test a Different Polymerase

The seventh step is to test a different polymerase. Some polymerases are more tolerant to inhibitors than others. A polymerase that is engineered for inhibitor tolerance may not need an additive. The new polymerase should be tested with the positive control and the sample.

Step 8: Test a Different Purification Method

The eighth step is to test a different purification method. The purification method may not remove the inhibitor. A different purification method may remove the inhibitor more effectively. The new purification method should be tested with the positive control and the sample.

Step 9: Test a Different Detection Chemistry

The ninth step is to test a different detection chemistry. The additive may interfere with the detection chemistry. A different detection chemistry, such as a different dye or a different probe, may be compatible with the additive.

Step 10: Escalate

The tenth step is to escalate the problem to a supervisor or a laboratory manager. The escalation should include the record system, the matrix, and the troubleshooting results. The supervisor should review the information and recommend a different approach.

Common Failure Patterns in Additive Use

Failure Pattern 1: The Additive Does Not Restore Amplification

The additive does not restore amplification if the sample is inhibited and the additive does not bind the inhibitor. The cause is usually a mismatch between the additive and the inhibitor. The solution is to test a different additive or to use a different purification method.

Failure Pattern 2: The Additive Inhibits the Positive Control

The additive inhibits the positive control if the concentration is too high. The solution is to reduce the concentration or to use a different additive. The concentration should be tested in a range.

Failure Pattern 3: The Additive Interferes with the Detection

The additive interferes with the detection if the fluorescence is reduced or the threshold is delayed. The solution is to test the additive with the detection chemistry and to use a different additive.

Failure Pattern 4: The Additive Is Not Reproducible

Failure Pattern 5: The Additive Works but the Yield Is Low

The additive works but the yield is low if the amplification is delayed or the product is weak. The cause is usually a suboptimal concentration or a suboptimal annealing temperature. The solution is to test a range of concentrations and to adjust the annealing temperature.

Practical Implementation Steps for the Decision Matrix

Step 1: Build the Matrix

The matrix should be built with the sample matrices and the candidate additives. The matrix should be based on the documented mechanisms and the compatibility profiles. The matrix should be posted in the laboratory and updated with the results of each experiment.

Step 2: Select the Additive

The additive should be selected based on the matrix and the sample type. The top two additives should be selected for testing. The selection should be recorded in the record system.

Step 3: Test the Additive

The additive should be tested with the positive control, the negative control, the sample, and the spike-in control. The concentration should be tested in a range. The results should be recorded.

Step 4: Update the Matrix

The matrix should be updated with the results of the experiment. The score should be adjusted based on the results. The matrix should be used for the next experiment.

Step 5: Report the Results

The results should be reported in the methods section of any publication. The additive name, the concentration, the lot number, and the manufacturer should be reported. The thermal cycling conditions and the detection chemistry should also be reported.

Records and Measurements for the Decision Matrix

Records to Keep

The following records should be kept for each experiment:

The additive name, lot number, and concentration
The sample type and extraction method
The polymerase name, lot number, and concentration
The buffer name and concentration
The detection chemistry
The thermal cycling conditions
The threshold cycle and the amplification curve
The positive control and the spike-in control results

Measurements to Make

The following measurements should be made for each experiment:

The threshold cycle for the positive control
The threshold cycle for the sample
The threshold cycle for the spike-in control
The amplification efficiency
The product yield

Quality Controls

The following quality controls should be used for each experiment:

A positive control without the additive
A positive control with the additive
A negative control without the template
A spike-in control with the sample

Safety and Regulatory Context

Biosafety

PCR additives are generally safe, but they should be handled with standard laboratory safety practices. The additives should be stored in a clean, dry place and should be handled with gloves and eye protection. The additives should not be ingested or inhaled. The laboratory should follow the biosafety principles described in the Biosafety in Microbiological and Biomedical Laboratories manual.

Recombinant DNA

Laboratory Standards

Professional Escalation Criteria

When to Escalate

What to Report

The researcher should report the following information:

The additive name and concentration
The sample name and concentration
The polymerase name and concentration
The buffer name and concentration
The thermal cycling conditions
The results of the positive control and the spike-in control

What to Expect

Frequently Asked Questions

What is the best PCR additive for inhibitor tolerance?

The best additive depends on the inhibitor type and the polymerase. BSA is the most common additive for heme, fatty acids, and phenolic compounds. DMSO is used for GC-rich templates and for reducing the melting temperature. The additive should be tested with the specific sample and the specific polymerase.

How much BSA should I add to my PCR?

The concentration of BSA should be tested in a range. A common starting concentration is 0.1 to 1.0 mg/mL in the final reaction. The optimal concentration depends on the inhibitor concentration and the polymerase.

Can I use DMSO with a proofreading polymerase?

DMSO can be used with a proofreading polymerase, but the concentration should be lower than that used with standard Taq. DMSO can reduce the proofreading activity, and the concentration should be tested.

Does BSA interfere with SYBR Green?

BSA can bind to SYBR Green and reduce the fluorescence. The concentration of BSA should be tested with the SYBR Green, and the dye should be used at the recommended concentration.

What is a spike-in control?

A spike-in control is a known amount of a control template that is added to the sample. The control template is amplified with a different primer pair. The spike-in control is used to determine whether the sample inhibits the PCR.

Can I use an additive with digital PCR?

An additive can be used with digital PCR, but the concentration should be tested. The additive can affect the volume and the detection, and the reaction should be tested.

What should I do if the additive does not work?

If the additive does not work, the concentration should be increased or a different additive should be tested. The sample should be tested with a positive control and a spike-in control.

How do I report the additive in a publication?

The additive should be reported in the methods section. The name, the concentration, the lot number, and the manufacturer should be reported. The thermal cycling conditions and the detection chemistry should also be reported.

Using the Evidence

Source	Best use in this topic	Important limitation
Molecular Biology and Laboratory Methods	official guidance	Check the linked page for current local requirements
Biosafety in Microbiological and Biomedical Laboratories	official guidance	Check the linked page for current local requirements
NIH Guidelines for Recombinant or Synthetic Nucleic Acid Molecules	official guidance	Check the linked page for current local requirements

Related Molecular Biology Guides

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.
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Integrative RNA profiling of TBEV-infected neurons and astrocytes reveals potential pathogenic effectors.. Computational and structural biotechnology journal, 2022.
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This article is educational and does not replace validated laboratory procedures, institutional biosafety review, manufacturer instructions, or professional interpretation.