Surface Passivation of PCR Chambers

To avoid inhibition of the enzyme (polymerase) and adsorption of DNA (template and product), surface passivation on the PCR was needed. It was found that native silicon is an inhibitor of PCR and an oxidized silicon (Si02) surface was required to provide the best passivation [943]. 

In a later report, inhibition of PCR in Si-glass PCR chips was found to be mainly caused by the adsorption of the Taq polymerase, rather than by the adsorption of DNA [299]. It was also found by XPS analysis that the primary PCR inhibitor in a glass PCR chamber was Cr, which was involved in the microfabrication process. The highest Cr concentration that could be tolerated was found to be 0.1 M [932]. 

Hemoglobin and heparin present in blood samples are also PCR inhibitors. In one report, these inhibitors were removed from yeast cells (used as the model for blood cells) after DEP cell retention. The yeast cells were retained by DEP, whereas bovine hemoglobin (1 mg/mL) and heparin (13 pg/mL) were washed away [933], 

Four coatings, such as PEG (8.5% w/v), PVP (2.5% w/v), HEC, and EPDMA, were evaluated for PCR on glass chips. It was found that the amount of PCR products were 13%, 78%, 0%, and 72%, respectively, when it was 100% using a conventional PP tube. These values were also compared to 50-120% when only silanization was used for passivation. While the first three are dynamic coatings, the last one is an adsorbed coating [935]. 

In another report, it was found that the addition of PEG 8000 or PVP 40 in the PCR mixture produced a significant surface passivation effect in either native or Si02-precoated Si-glass chips. Using this passivation method, PCR of the nitric oxide synthase gene (human endothelial) in human lymphocytes was demonstrated [936]. 

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