Characteristics of whispering gallery mode in microsphere covered antigen-antibody layer at attenuated-total-reflection configuration

Microresonators have attracted attention over the past few years because label-free optical biosensors base on them have potential in pathogen virus and healthcare and pharmaceuticals and the food industry. Whispering gallery mode (WGM) microresonators have advantages of an ultra-high Q-factors and a mass production capability of a sensor chip. This work presents a variation of WGM spectra depending on each antibody and antigen bound to a polystyrene microsphere, which allowed us to evaluate optically the thickness and the refractive index of the antigen antibody layer from a shift of the WGM spectra peak. Furthermore, the split variation of the WGM spectra peak by the adsorption of the antigen antibody was evaluated by polarization and the excitation position. The split variation of the scattered light peak depended on the direction circumnavigating microsphere.