Identification of Analytical Singularity in a Non‐Plasmonic Nanosensing System

Abstract

Nanosensors based on small particles are essential in the advancement of countless areas involving biomedical and fundamental physics. While the Clausius-Mossoti relation reveals the natural advantage of plasmonic nanoparticles as a singularity-generating device with the possibility of achieving ultra-high sensitivity, practical issues such as metallic losses and sensor con guration often preclude them from being considered as the ideal nanosensor. Non-plasmonic, or dielectric nanoparticles, though have distinct advantage in small material loss and design exibility, cannot have a pole in the Clausius-Mossoti relation. Here, we demonstrate how such limitation on dipolar resonance of a dielectric nanoparticle can be fundamentally overturned if the nanoparticle is placed in an assisting dielectric cavity. Using the pseudo-orthonormal eigenmode method (POEM), we pinpoint the singularity of such non-plasmonic system in the complex frequency plane. The framework of the study provides not only analysis of the underlying physics, but also generates a set of guidelines to facilitate the device optimization in the real world. For numerical simulation, we use nite-difference time-domain (FDTD) method to demonstrate giant sensitivity of the structure when it operates around the pole.