Whispering-Gallery Mode Based Biosensing Using Quantum Dot-Embedded Microspheres
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Highly sensitive, miniature biosensors are desired for the development of new techniques for biological and environmental analyte sensing. One potential approach uses the detection of optical resonances, known as Whispering Gallery Modes (WGMs), from quantum dot embedded polystyrene microspheres. These modes arise from the total internal reflection of the quantum dot emission light within the high index polystyrene microsphere, to produce narrow spectral peaks, which are sensitive to refractive changes in the immediate vicinity of the microsphere surface. The high refractometric sensitivity of the WGMs in these microspheres offers potential for remote detection of molecules adsorbed onto or bound to the microsphere surface without the need for direct coupling of the light via an optical fiber. The sensitivity of these modes has been shown to exceed the theoretical sensitivity of a homogeneous microsphere, using a Mie theory model. This enhancement is believed to be due to the embedded layer of quantum dots at the surface of the microspheres. A model was developed to demonstrate that the embedded QDs could be modeled as a high index outer layer to explain the observed WGM spectra and explore the sensitivity of the modes. In this work, we extend this idea to multiple layers to model the effects of protein adsorption or binding to the surface. The theoretical results are shown to provide a close fit to our previous experimental results. 2010 Copyright SPIE - The International Society for Optical Engineering.
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Colloidal Quantum Dots for Biomedical Applications V