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Confirmatory detection of diseases, such as HIV and HIV-associated pathogens in a rapid point-of-care (POC) diagnostic remains a goal for disease control, prevention, and therapy. If a sample could be analyzed onsite with a verified result, the individual could be counseled immediately and appropriate therapy initiated. Our group is focused on developing a microfluidic "lab-on-a-chip" that will simultaneously identify antigens, antibodies, RNA, and DNA using a single oral sample. The approach has been to design individual modules for each assay that uses similar components (e.g., valves, heaters, metering chambers, mixers) installed on a polycarbonate base with a common reporter system. Assay miniaturization reduces the overall analysis time, increases accuracy by simultaneously identifying multiple targets, and enhances detector sensitivity by upconverting phosphor technology (UPT). Our microfluidic approach employs four interrelated components: (1) sample acquisition-OraSure UPlink collectors that pick-up and release bacteria, soluble analytes, and viruses from an oral sample; (2) microfluidic processing-movement of microliter volumes of analyte, target analyte extraction and amplification; (3) detection of analytes using UPT particles in a lateral flow system; and (4) software for processing the results. Ultimately, the oral-based microscale diagnostic system will detect viruses and bacteria, associated pathogen antigens and nucleic acids, and antibodies to these pathogens.

An easy to implement, thermally-actuated, noninvasive method for flow control in microfluidic devices is described. This technique takes advantage of the phase change of the working liquid itself—the freezing and melting of a portion of a liquid slug—to noninvasively close and open flow passages (referred to as a phase change valve). The valve was designed for use in a miniature diagnostic system for detecting pathogens in oral fluids at the point of care. The paper describes the modeling, construction, and characteristics of the valve. The experimental results favorably agree with theoretical predictions. In addition, the paper demonstrates the use of the phase change valves for flow control, sample metering and distribution into multiple analysis paths, sealing of a polymerase chain reaction (PCR) chamber, and sample introduction into and withdrawal from a closed loop. The phase change valve is electronically addressable, does not require any moving parts, introduces only minimal dead volume, is leakage and contamination free, and is biocompatible.

It is not surprising that the use of buoyancy as a driving force in microfluidic systems has attracted little or no attention. Buoyant forces are proportional to the volume and do not scale favorably as the device size is reduced. Nevertheless, in certain biotechnological applications, one can produce sufficiently large buoyancy forces to generate fluid motion at velocities on the order of mm/s even in conduits with equivalent diameters of a few hundreds of microns. One example is the thermal polymerase chain reaction (PCR) for DNA amplification. In this process, the reagents’ temperature varies from about 55°C to 94°C. Such large temperature variations can induce significant buoyant forces. Another class of systems that can be driven by buoyant forces is rotating laboratories on a chip (lab on a CD). In such laboratories, large centrifugal accelerations may induce significant buoyant forces even when the temperature variations are relatively small. These temperature variations can be used to propel and control fluid flow.Copyright © 2004 by ASME