Label-free nanoparticle sensors based on a triple-layer-coated microsphere structure

摘要： We present a design for a sensitive, label-free nanoparticle sensor based on triple-layer-coated microsphere resonators. The surfaces of the microsphere structure are coated with three layers that have high, low, and high refractive indexes from inside to outside, respectively. We theoretically and numerically investigate two cladding modes, we call the inner mode and outer mode. The resonance wavelengths of the two modes are used to detect the resonance wavelength shift caused by a single-nanoparticle. Numerical calculation suggests that if we change the thickness of the middle layer, the device offers another degree of freedom to obtain higher detection sensitivity. We build a model to accurately describe a nanoparticle close to the microsphere. The method for the sensors may promote the design of biosensing applications.