Whispering gallery micro-global positioning system for nanoparticle sizing in real time

Abstract

We have devised a simple means for determining the size of a nanoparticle in one binding event (i.e., real time) by utilizing two polar modes of a slightly eccentric Whispering Gallery Mode (WGM) spheroidal resonator. The ratio of shifts of these modes locates the absolute latitude angle at which a nano-particle binds. From this location, the size of the nanoparticle is calculated using the reactive sensing principle. Although our latitude-only micro-global positioning scheme is applied to nanoparticle sizing using slightly eccentric spheroids in aqueous solution, this approach can be applied to WGM micro-resonators having a variety of shapes.