Inhibition of on-chip PCR using PDMS-glass hybrid microfluidic chips

In the course of developing a microfluidic analytical platform incorporating the polymerase chain reaction (PCR) and subsequent capillary electrophoresis (CE) analysis for a variety of bio-assays, we examined PCR inhibition through surface interactions with the chip materials. Our devices perform PCR in a three-layer chip, a glass-poly(dimethylsiloxane)-glass sandwich in which the poly(dimethylsiloxane) (PDMS, a silicone rubber) layer is used for pneumatic membrane pumping and valving of the PCR reagents. Initial on-chip PCR-CE tests of BK virus replicated in multiple uncoated chips showed variable results, usually yielding no detectable product at the target sample concentrations used. Subsequent chip-flush experiments, where water or reagents were flushed through a chip and subsequently incorporated in off-chip PCR, highlighted bovine serum albumin (BSA) amongst other pre-treatments, chip materials and PCR recipes as being effective in mitigating inhibition. When the BSA channel pre-coating was applied to on-chip PCR-CE experiments, a substantial improvement (10x to 40x) in signal-to-noise (S/N) of the CE product peak was conferred, and was shown with high confidence despite high S/N variability. This is the first study to quantitatively examine BSA's ability to reduce inhibition of PCR performed on PDMS chips, and one of very few microfluidic PCR inhibition studies of any kind to use a large number of microfluidic chips (similar to 400). The simplicity and effectiveness of our BSA coating suggest that passivating materials applied to microfluidic device channel networks may provide a viable pathway for development of bio-compatible devices with reduced complexity and cost.