There is demand for an inexpensive, reliable, and expedient fabrication of microfluidic devices for biosensors such as devices for detetion of bacterial spores. We developed non-lithographic fabrication method that utilizes readily available equipment and meterials: i.e. LaserJet printers, Poly(dimethylsioloxane) (PDMS), glass slides, a plasma generator and a vacuum oven. Our fabrication procedures do not require clean-room environment and specialized equipment for photolithography.

The effects of oxygen plasma treatment on the adhesion of glass slides to PDMS is studied. Smooth substrates of PDMS and glass slides are treated with oxygen plasma with varying power levels, exposure time, pressure levels, and gas composition. The treated glass and PDMS were brought together in contact and than cured in a vacuum oven at 120 deg C. The adhesion of the PDMS blocks to the glass was evaluated semi-quantitatively on a trinary scale: 0 for little or no irreversible adhesion, 1 for partial adhesion, and 2 for complete adhesion. Multi-variable analysis depicts regions of optimal conditions for proper adhesion. Low power levels resulted in poor adhesion. Higher power levels provided better adhesion, which, however, was compromised in cases of long exposure times. Higher power levels require relatively short times (e.g. 15-30 seconds) to prevent over curing. Optimal pressure and gas composisitions are also necessary for quality adhesion. Adhesion under optimal conditions yields reliable and expedient construction of PDMS based microfluidic devices.

We used the non-lithographic fabrication methods which were developed in our laboratory, for the preperation of microfluidic devices for detection of bacterial spores and vegitative bacteria. We were able to detect as few as 10-5 spores in a single injection.

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