13 October 2006 UV imaging of biochips: limitations of contrast
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Ultraviolet (UV) imaging is a bright field technique that uses short wavelengths to yield higher resolution than a conventional imaging. The absorption of proteins at 280nm and DNA at 260nm gives additional contrast without staining. Combined with modern video equipment, these two facts render UV imaging a useful tool in live cell imaging whose popularity is low due to the high cost of the lenses and the UV sensitive camera required. The need of wavelengths selection by a monochromator is also a limitation. On the contrary, the new AlGaN based imagery is intrinsically very sensitive to UV and prevents the use of a spectroscope. It allows UV imaging at extremely low flux minimising damage for biological samples. In the frame of biological threat, security systems require label free biochips for rapid detection. Surface Plasmon Resonance (SPR) imaging is a standard method proposed for antibody / antigen recognition but the optical set-up based on reflection requires a large optical path, and detection is only efficient for biological compounds close to the surface. In case of cells or bacteria whose typical dimensions are larger, UV imaging is a compact and suitable method. The first experiments shows that absorption takes place even for extremely low quantity of DNA when chips are covered with dielectric mirror whereas scattering is the largest contribution to contrast in case of BK7 slides. In case of proteins deposition on reflecting slides, absorption is lower than for DNA for a given molecular weight but spots still exhibit large contrast.
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Jean-Luc Reverchon, Jean-Luc Reverchon, Charly Meyer, Charly Meyer, Giovanni Mazzeo, Giovanni Mazzeo, Simone Cassette, Simone Cassette, } "UV imaging of biochips: limitations of contrast", Proc. SPIE 6398, Optically Based Biological and Chemical Detection for Defence III, 63980Q (13 October 2006); doi: 10.1117/12.689965; https://doi.org/10.1117/12.689965

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