Phase change based microfluidic components for lab -on -a -chip.

Abstract

Microfluidics based lab-on-a-chip devices are receiving considerable attention for point of care and high throughput biochemical analyses. The construction of these systems involves the development of individual miniaturized components and their successful integration into a self-contained system. An active microvalve that uses a meltable piston to obstruct fluid flow in a microfluidic channel has been developed. This phase change valve is simple to operate and requires no additional fabrication steps. The valve is inherently latched, reusable, and leak-proof (to at least 250 psi), and can be electronically addressed using resistive heaters. The latched property of the phase valves has been exploited to perform zero energy on-chip storage of a restriction-digestion reaction pre-mixture. Valves have been used to seal a high temperature reaction chamber to prevent evaporation and successful DNA amplification using PCR has been achieved. A practical implementation of the phase change valve array analogous to the address-data bus has also been presented. An integrated microfluidic device capable of performing a variety of genetic assays has been developed. The device integrates fluidic and thermal components such as heaters, temperature sensors, and addressable valves to control two nanoliter reactors in series followed by an electrophoresis separation. This combination of components is suitable for a variety of genetic analyses. As an example, we have successfully identified sequence-specific hemagglutinin A subtype for the A/LA/1/87 strain of influenza virus. A self-contained thermopneumatic actuation mechanism for phase change piston has been demonstrated. This actuation mechanism that uses two phase change pistons with an air pocket between them. This eliminates the requirement for large air chambers and high temperatures associated with traditional thermopneumatic actuation. The motion of a two component wax piston that does not coat the walls has also been characterized. To facilitate mass fabrication of chemically and thermally sensitive materials including phase change pistons a microfabrication technique that uses a microstencil has been developed. This technique has been used to pattern silicon, glass, and polymer substrates. As an initial demonstration of this technique we have patterned wax, cells, proteins, and Cytop(TM) that cannot be patterned with traditional microfabrication techniques due to the harsh chemicals used in those processes.