Microfabrication for Biomedical Research

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There is a strong interest in the simultaneous and rapid detection of a multiple biomarkers in a single biological sample. This interest has been one of the driving forces behind the development of microfluidic devices for biomedical applications. The move to these smaller-scale systems has a number of advantages. First, they are capable of analyzing smaller sample volumes. Second, in applications such as capillary electrophoresis the microfluidic system can achieve the same separation resolution in much less time than a larger-scale system. Finally, the reduced size of the analysis setup raises the possibility of developing portable analytical devices. One device under development is capable of measuring eight different electrophoretic runs simultaneously. Another device under development is the miniaturization of a luciferase immunoprecipitation (LIPS) assay that looks for immune response in serum samples. Other interests of our group include the design and development of devices capable of analyzing the secretions and physiology of single cells. Our facilities have now developed to a point where we are able to advise and collaborate with both intramural and extramural investigators on how to produce microfluidic devices that address their specific needs. In collaboration with scientists at NIST, and using the microfabrication facilities at NIST, we are able to make micrometer-scale glass-encapsulated microfluidic systems with any desired two-dimensional configuration, as well as templates to stamp thermoplastics or mold elastomers into microfluidic devices. This year, we have further developed technology on-campus for forming, sealing, and coating microfluidic channels in thermoplastics and elastomers from these templates. We are also in the process of setting up a basic lithography system in our laboratory, intended for rapid fabrication of single-layer structures and templates with dimensions down to approximately 25 micrometers. In addition, we continue work on a project aimed at miniaturizing the LIPS assay, which uses a fusion protein consisting of Renilla luciferase and an antigen of interest to probe for antibodies in human serum. In its current format, the assay is performed in a 96-well filter plate, and has been shown effective in detecting a number of autoimmune conditions and infectious diseases. Moving the assay to a microfluidic format could significantly speed the analysis, permit multiplexing, and also facilitate the application of this assay to point-of-care diagnostics. Experiments using cell extracts containing the fusion protein and commercial anti-CFLAG antibodies in lieu of serum had shown that the positive signal levels are acceptably high even in the miniaturized format. This year, our efforts focused primarily on increasing measurement reproducibility, which involved redesign of the luminescence measurement setup, adjustment of the channel surface chemistry, buffer optimization, and substantial refinement of flow control within the microchannel, as well as other improvements to the measurement protocol. As a result, our preliminary measurements on serum samples now show less than 10% variation between runs using ten minute incubation times in a microchannel. In the near future, we plan to undertake measurements on a panel of samples to verify correspondence between the microfluidic assay and the original well format.