The multilayer cluster micro-sphere biosensor for single nanoparticle detection by using WGM excitation

Abstract

The biological properties of Whispering-Gallery-Mode (WGM) -based biosensors have improved significantly in recent years. This work presents a new structure for WGM-based biosensors in the operating wavelength range of 450 nm to 550 nm. The structure provided consists of different metal-semiconductor layers on a spherical SiO₂ substrate. The proposed structure uses spherical silver nanoparticles on the graphene layers to strengthen the evanescent field profile. We show that the interaction of WGM evanescent field with analytes leads to the absorption of these particles at the resonator's surface. Also, the six-layer graphene in this structure has improved the sensitivity of the biosensor to biological factors. This proposed sensor has the ability to identify virus particles and single proteins with small dimensions, including the protein S and bovine serum albumin (BSA). It is worth mentioning that the S protein is present in the biological structure of the coronavirus. 3D finite-difference time-domain (FDTD) method was used to analyze the effect of proposed solutions on optical performance such as resonance wavelength shift and relative electric field intensity. The structure without silver nanoparticles has a wavelength shift of 0.36 nm and an electric field intensity of 6.8. But these values increase to 0.98 nm and 12.5 respectively in the presence of silver nanoparticles. Also, Fabrication method is described in details.