Microsphere based optical biosensors

Abstract

Optical microsphere resonators have recently utilized in quantum optics, laser science, spectroscopy, and optoelectronics and attracted increasing interest due to their unique optical properties. Microspheres possess high quality factor (Q-factor) optical morphology dependent resonances, and have relatively small volumes. Q-factor can be defined as how sharp morphology dependent resonance in the elastic scattering spectrum. High-Q morphology dependent resonances are very sensitive to the refractive index change and microsphere uniformity. These tiny optical cavities, whose diameters may vary from a few to several hundred micrometers, have resonances with reported Q-factors as large as 3 x 109. Due to their sensitivity, morphology dependent resonances of microspheres are also considered for biosensing applications. For instance, binding of a protein or other biomolecules can be monitored by observing the wavelength shift of morphology dependent resonances. A biosensor, based on this optical phenomenon, can even detect a single molecule if a good system design is achieved. In this work, elastic scattering spectra from the microspheres of different materials are experimentally obtained and morphology dependent resonances are observed. Furthermore, the morphology dependent resonances of microspheres for biosensor applications were studied theoretically.|Keywords: Biosensor, Microsphere, Morphology Dependent Resonances.