PCR reagents: choosing the polymerase, the nucleotides and the mix

Choosing the components, and what a pcr kit includes

1. Fidelity or robustness in the polymerase. High fidelity enzymes with proofreading are required for cloning, sequencing libraries and anything where an error is carried forward. Robust, non-proofreading enzymes tolerate inhibitors and awkward templates and suit diagnostics and screening where an occasional error is irrelevant. The choice is the application's, not the catalogue's.
2. Hot start, almost always. A hot start enzyme is inactive until the first denaturation, which suppresses primer dimers and non-specific products formed while reactions are set up at room temperature. The premium is small and the improvement in specificity is reliable.
3. Nucleotide quality and storage. The nucleotide mix is a small part of the cost and a common cause of quiet failure, because repeated freeze and thaw cycles degrade it. Buy a quality-tested mix, aliquot it once on arrival, and suspect it early when a reaction that used to work stops working.
4. Master mix or components. A master mix reduces pipetting steps and therefore variation, and it is usually the better buy for routine and high-throughput work. Separate components allow magnesium, nucleotide and enzyme concentrations to be tuned, which matters during method development.
5. Primers and the design step. No reagent recovers a poorly designed primer pair. Check specificity against the genome rather than against the target alone, check for dimers and hairpins, and match melting temperatures. This costs minutes and prevents most non-specific products.

Contamination control

Amplification generates enormous numbers of copies, and a laboratory that has contaminated its reagents will produce convincing results from blank samples. Separate pre-amplification and post-amplification areas, use filter tips, and run no-template controls on every plate.

Where contamination is suspected, replacing every reagent aliquot at once is faster than testing them one by one, and cheaper than the results lost in the meantime.

A real time PCR master mix needs more specification

Real-time amplification adds a detection chemistry, whether an intercalating dye or a probe, and each has its own specificity and multiplexing consequences. A dye reports any double-stranded product including dimers, which is why a melt curve is part of the result.

Reverse transcription adds another enzyme and another set of variables, and the choice between a one-step and a two-step protocol affects both convenience and the ability to re-use the complementary DNA.

A high fidelity polymerase, and when a high fidelity dna polymerase is the wrong one

A high fidelity dna polymerase is proofreading: it carries 3' to 5' exonuclease activity and misincorporates orders of magnitude less often than Taq, which is what cloning, library preparation and any product you intend to sequence require. It is the wrong choice where the error rate does not matter and the assay depends on something Taq does: a hot-start Taq blend tolerates dirtier templates, and the A-tailing that TA cloning needs comes from a non-proofreading enzyme. Quotes for a high fidelity polymerase are usually per unit rather than per reaction, so convert to reaction cost before you compare them.

rt pcr plates, and the consumable's part in the result

A real time PCR plate is an optical consumable, not a container. Wall thickness and clarity set how much signal reaches the detector, the skirt and dimensions have to match the block so every well makes the same thermal contact, and the seal decides whether the outer wells evaporate over forty cycles. Mixing plates and seals from different suppliers is the usual cause of edge effects that get blamed on the assay. Match the plate to the instrument's own specification, keep one seal type, and if a well pattern appears in the data, change the consumable before the primers.

mycoplasma detection pcr, and what a clean result requires

A mycoplasma PCR uses primers in a conserved 16S region to cover the species that infect cultures, and it is sensitive enough that the controls decide whether the result is usable. A positive control at a defined copy number shows the reaction worked; a negative extraction control catches reagent contamination; and an internal amplification control shows the sample did not inhibit. Test the supernatant of a culture grown without antibiotics for several days, since antibiotics suppress the organism without clearing it and a treated culture can read negative while still infected.

pcr machine brands and what actually differs

pcr machine brands differ mainly in block uniformity, ramp rate and whether the consumable format is proprietary, and the last has the largest effect on running cost. A thermal verification with a calibrated probe is what shows whether a block still holds the programme it displays.

A chlorine reagent and a field determination

A chlorine reagent develops a colour proportional to free or total chlorine and is read on a colorimeter, which is why the reagent and the instrument are matched as a system with a stated range. Chlorine dissipates from a sample quickly, so the determination is made at the point of sampling rather than at a bench.

Common questions

Which PCR polymerase should I use?

A high fidelity proofreading enzyme for cloning, sequencing libraries and anything where errors are carried forward; a robust non-proofreading enzyme for diagnostics and screening where inhibitor tolerance matters more than fidelity.

Do dNTPs go bad?

They degrade with repeated freeze and thaw cycles, which is a common and quiet cause of a reaction that used to work failing. Aliquot on arrival and suspect the nucleotide mix early.

Is a master mix worth the premium?

For routine and high-throughput work, usually, because fewer pipetting steps means less variation. Separate components are better during development, when magnesium and nucleotide concentrations need tuning.

Why use a hot start enzyme?

Because it stays inactive until the first denaturation, suppressing primer dimers and non-specific products that form while reactions are assembled at room temperature. The specificity gain is reliable and the cost is small.

Which pcr probes does the chemistry allow?

A dual labelled hydrolysis probe is the default and needs a polymerase with strong five prime exonuclease activity, which rules out some high fidelity enzymes. A molecular beacon or a displacement design tolerates enzymes that a hydrolysis probe does not, and an intercalating dye needs no probe at all but cannot multiplex. Match the probe to the enzyme before ordering both, because a mismatch shows up as an amplification curve with no signal.

Browse by service class

• Compare Gene synthesis on advertised prices