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21 February 2008 Detection and quantification of lipid membrane binding on silica micro-tube resonator sensor
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Silica micro-tube resonator is a very attractive biosensor platform for label-free detection of bio-molecules by combining high sensitivity and simple fluidic handling. We report the study of lipid membrane binding on micro-tube sensor that is probed by a prism coupling technique. Prism coupling to the micro-tube resonance modes allows thick micro-tube to be used and the selectivity of high-sensitivity modes. We were able to identify and probe a special resonance mode that has very high Electrical field at the boundary of the fluid and the inner tube wall. Unlike typical WGM modes, such resonance modes also have very high Electrical field extending into the lower index fluid region, thereby providing exceptionally high sensitivity to the fluid's refractive index change. We used this type of resonance mode to detect the formation of single bilayer lipid membrane on the inner tube wall. With 4-5nm POPC lipid membrane with refractive index around 1.46 absorbed on the inner wall, we can observe the resonance peak shift around 44pm. Mie scattering simulation of the resonance peak shift due to the bio-film absorbed onto the inner wall agrees very well with the experiment results. We also observed resonance peak shift with the membrane protein Annexin V bonding to the lipid membrane. With the present Q factor 6×104 at 1.55μm wavelength, we estimate that our devices can detect the presence of 0.1nm thick absorbed film on the inner wall of the tube. The device's sensitivity can be greatly enhanced by switching the working wavelength from infrared wavelength to visible wavelength where water absorption is minimized.
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Tao Ling, Sheereen Majd, Michael Mayer, and L. Jay Guo "Detection and quantification of lipid membrane binding on silica micro-tube resonator sensor", Proc. SPIE 6862, Single Molecule Spectroscopy and Imaging, 68620B (21 February 2008);

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