Monolithic structures for integrated microfluidic analysis. (2001)

Over the past decade there has been increased interest in the development of miniaturized chemical analysis systems. This research concentrates on developing a microfluidic handling and reaction system for DNA analysis using surface micromachining of plastics, which are capable of performing sample injection, metering, transport, and reaction operations, all integrated on a microelectronic substrate. The batch lithographic plastic process is a low temperature and CMOS compatible process that makes integration of microfluidic and circuit elements possible. These fluidic structures are also optically transparent and can range from 0.5mum to 100mum in height. The fluidic components have been fabricated on top of silicon, glass, and polycarbonate wafers. Mechanical and biocompatibility tests indicate that the plastic components are suitable for DNA analysis instrumentation. Using this polymer technology, a surface micromachined sample injector incorporated with stop valves have been constructed. The sample injector devices are based on electrolysis pumping mechanism where oxygen bubbles are generated in the inner electrode to raise enough pressure to overcome the pressure barrier build up by the stop valves. Stop valves have been designed to build up pressure barrier caused by the capillary forces developed at the abrupt enlargement of channels. Pressure barrier of 6MPa has been recorded on a 10mum gap vertical stop valve. The horizontal stop valves have been designed to be asymmetric and have exhibited an unidirectional flow behavior. When integrated with the stop valves and flow restriction, these sample injectors are capable of loading liquid samples with injection current of several muA and low power consumption of 100muW. A monolithic sample injector incorporated with hydrophobic patch has been constructed in a 6 mask polymer process. Sample injection has been successfully demonstrated with the hydrophobic valve actuated when the bubble was formed very quickly with electrode current <italic>I<sub>c</sub></italic> > 3muA. Unlike the horizontal and vertical valve, the hydrophobic valve impedes capillary-induced creep flow around the bubble edge along the channel sidewalls. With this hydrophobic valve, the liquid sample is completely separated from the liquid plug behind the patch. In addition, this kind of injector is capable of transporting the liquid plug after the valve is actuated. Finally, a 7nL monolithic PCR reaction chamber with on-chip heater and temperature sensor has been constructed on top of glass substrate. The permeability and evaporation of liquid vapor has been greatly reduced using a 2-mm thick epoxy layer deposited on top of the chamber. Double stranded DNA (C57BL/6J) fluorescently tagged with SYBR Green intercalating dye was mixed with primers (D6MT102) and PCR reagents. The mixed solution underwent 52 thermal cycles (94&deg;C/15s, 55&deg;C/25s, 72&deg;C/15s). With PID control scheme, heating rate of 13&deg;C/s as well as cooling rate of -24.6&deg;C/s have been achieved. The power consumption of reaction chamber was found to be low (263mW at 94&deg;C). PCR product was detected by a photo-multiplier tube which measured the increase in fluorescence caused by the binding of SYBR Green to the newly amplified ds DNA. Fluorescence signal revealed that 13 times of the DNA was successfully amplified.