Polymer-Silicon Microcantilevers Serve as Ultrasensitive IR Detectors
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The researchers fabricated their molecularly imprinted polymer (MIP) devices by pressing a monolayer of RBCs of a given antigen type onto a thin layer of polyurethane. The polyurethane was pre-deposited on the sensor of a quartz microbalance for use in later measurements. The cured polymer bears the imprint of the cells, and after removal of the cell layer, the MIP retains toroid shapes characteristic of the cells, as seen by atomic force microscopy. Cell adsorption on the MIPs was then measured by monitoring the response of the quartz microbalance electrode beneath the MIPs relative to an electrode under an unimprinted surface. With this technique, the researchers showed that the greatest number of cells was adsorbed onto MIPs that had been imprinted with cells of the same blood type. This selectivity is especially remarkable, they said, in that all blood cells show nearly the same shape and are highly deformable, and the changes in imprint morphology caused by surface structures are extremely subtle. The researchers said that excess hydroxyl groups on the polyurethane substrates interact with the sugars of the antigens on the imprinting cells, creating a template for
selective recognition on the molecular scale through increased hydrogen bonding capacity for the appropriate antigen. KRISTA L. NIECE
mK—has been achieved with bimaterial microcantilevers combining silicon and gold as the high-α and low-α components, respectively, but current applications demand better performance. Recently, however, Iowa State University researcher V.V. Tsukruk, Air Force Research Laboratory researcher T.J. Bunning, and their co-researchers have replaced the contemporary metal–silicon bimorphs with a polymer–silicon hybrid design with much larger interfacial thermal stresses, resulting in temperature resolutions approaching 2 mK and thermal sensitivities of ~2 nm/mK, unprecedented values for uncooled detection. As reported in the April 12 issue of Nano Letters (p. 730; DOI: 10.1021/nl0525305), the research team used plasma-enhanced chemical vapor deposition (PECVD) to selectively coat one side of silicon microcantilevers (~300 μm in length, ~30 μm in width, ~0.7 μm thick) commonly used in atomic force microscopy (AFM) with several highly cross-linked plasma polymers. In this publication, polystyrene (PS) is featured, and the PS-layer thicknesses were precisely controlled and confirmed by scanning electron microscopy and ellip-
Polymer–Silicon Microcantilevers Serve as Ultrasensitive IR Detectors Medical imaging, weather forecasting, targeting, and reconnaissance are a few of the critical applications for infrared (IR) detectors. With temperature resolution (the smallest measurable temperature difference) of ~10 mK, traditional IR detectors are essentially photon detectors that require cryogenic cooling, which hampers miniaturization and cost reduction. Uncooled IR detectors, based on thermal detection and a bimaterial microcantilever design, have been fabricated in recent years. The microcantilevers bend reversibly because interf
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