Planar poly(dimethylsiloxane) (PDMS)–glass hybrid microdevice for a flow-through polymerase chain reaction (PCR) employing a single heater assisted by an intermediate metal alloy layer for temperature gradient formation

In this study, we fabricate a hybrid planar microdevice to perform an on-chip flow-through polymerase chain reaction (PCR) constructed by assembling glass and poly(dimethylsiloxane) (PDMS) on which a serpentine microchannel is engraved. The proposed system employs a metal alloy slab, called Invar, which is basically a nickel iron alloy, sandwiched between the microdevice and a heater. Owing to the high thermal conductivity (10 W K−1 m−1) but notably low thermal expansion coefficient (1.6 × 10−6 K−1) of Invar, a stable temperature gradient was established on its surface. The Invar was placed on the heater in such a way that they made partial contact, with the rest of the Invar exposed to the air. A uniformly distributed temperature gradient, which ranged in temperatures from 57 °C to 95 °C, was first established on the Invar sheet, and a planar microdevice was directly placed atop the Invar sheet. The proposed system was successfully applied to amplify three targets: a 230 bp gene fragment from a plasmid vector, the first 282 bp of the interferon-beta (IFN-β) promoter from human genomic DNA, and a 409 bp long gene fragment in thyroid transcription factor-1 (TTF-1), which is used effectively as a marker for diagnosing lung and thyroid carcinomas, from human genomic DNA. All of the targets were amplified within less than 30 min. One microdevice was utilized repeatedly for multiple target amplifications by fine tuning the relative position of the Invar sheet on the heater.