Microfluidics studies the behavior of fluids at the microscale and the design of systems to take advantage of such behavior. A multidisciplinary field encompassing physics, chemistry, engineering, and biotechnology, microfluidics integrates sensors, actuators, and other electronics to create new applications.1–3 Importantly, new principles of fluid manipulation have enabled detection and handling of nanoliter fluid samples. In recent years, these principles have been applied to the development of lab-on-a-chip (LOC) systems.4, 5 A substantial challenge for such miniaturized systems—the size of a credit card—for point-of-care and on-site analysis lies in developing their ability to effectively detect analytes of interest. Small sample volumes and low concentrations common to microfluidic LOCs make high-sensitivity detection of critical importance. While conventional microscopy tools can easily meet these demands in a laboratory, developing portable systems requires integrated miniaturized detectors. Fluorescence is one of the most commonly used analytic techniques in the biosciences. It is based on emission of a dye at one wavelength when it is illuminated by another, shorter wavelength. Lack of integrated fluorescence detection is a major roadblock for many biotechnological assays in portable LOC format. In a typical microfluidic fluorescence immunoassay assay, fluorescently labeled antibodies are used to tag a specific antigen (e.g., bacteria, viruses, or other organic molecules of interest) in a microfluidic device. The excitation light stimulates the dye to fluoresce, and the characteristic emission wavelength, or color, is observed through a filter that suppresses excitation light, enbling the dye emission to be seen clearly. As shown in Figure 1, the orange light represents the dye emission and the green light Figure 1. Schematic of a lab-on-a-chip (LOC) for fluorescence analysis. PDMS: Poly(dimethylsiloxane).
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Aug 27, 2008
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