Two-layer microdevice for parallel flow-through PCRs employing plastic syringes for semi-automated sample injection and a single heater for amplification: Toward process simplification and system miniaturization

This paper reports on the fabrication of a two-layer microdevice for conducting on-chip parallel flow-through polymerase chain reactions (PCRs) equipped with a single heater and disposable plastic syringes for semi-automated sample delivery for the construction of a portable PCR microdevice. Identical shapes of disconnected spiral-like microchannels were engraved on two poly(dimethylsiloxane) (PDMS) substrates having varying thicknesses, and by rotating either one of the substrates 180°, they were aligned in such a way that one continuous sample flow was realized in a 3D configuration within a two-layer microdevice. Typical in vitro enzymatic amplifications were performed simultaneously in parallel on the microdevice by employing a single heater. Also, sample actuation module was miniaturized and its operation was semi-automated by employing portable plastic syringes as pumps. This system dispenses with the use of a bulky external apparatus such as a syringe pump, and also greatly simplifies the temperature control by utilizing a single heater, and therefore, downsizing the overall footprint of the device. Samples were injected into two inlets simultaneously and were successfully delivered through the entire length of the microchannels of over 2 m, mediated by portable plastic syringes. To investigate the feasibility of employing a single heater as well as to assess the reliability of the sample injection performance initiated by the plastic syringes, on-chip flow-through PCRs were performed using plasmid DNA as templates inside 2 m-long spiral microchannels constructed in a two-layer arrangement, as a proof-of-concept experiment. Target amplicons were successfully amplified simultaneously in parallel reactions inside the proposed microdevice in approximately 27 min with high reproducibility, confirming stable sample injection performance and reliable temperature control inside the microdevice. The proposed schemes could pave the way for device miniaturization, process simplification, and reaction parallelization, realizing a portable microfluidic device applicable for on-site and direct field uses.