High-Performance Refractive Index-Based Sensor Using Ellipsoid Ag–Au Nanoparticles

The nanoparticles’ localized surface plasmon resonance (LSPR) is sensitive to the surrounding medium refractive index change. Therefore, biosensing devices commonly use it as a refractive index-based sensor. In this work, an improvement strategy for the sensing performance of gold (Au) and silver (Ag) ellipsoid nanoparticles (NP-ELs) through controlling the size, aspect ratio (AR), and core–shell structure was proposed. The investigation was started by constructing a multiple oscillator model to derive the optical permittivity function and compute the absorption of nanoparticles via discrete dipole approximation (DDA). The change in position and width of the LSPR peak concerning the refractive index of the medium were calculated to determine the sensing performance. Sensitivity and figure of merit (FOM) were used to describe the sensing performance. As a result, the AR parameter of nanoparticles was found to be more dominant in increasing sensitivity and FOM compared to particle size. In the core–shell structure, the absorption spectrum is also affected by the shell thickness, particle size, and AR. Therefore, those parameters can tune the sensing performance of the Ag–Au NP-ELs. The maximum sensitivity obtained for Ag–Au NP-ELs was 597.7 nm/RIU with an FOM of 34 RIU $^{-{1}}$ . Therefore, the high performance of refractive index-based sensor proposed in this study opens a new gate for developing biosensors in future.