(563b) Aqueous Mercuric Ion Detection with Microsphere Optical Ring Resonator Sensors

We have developed a novel optical sensor based on fused silica microsphere ring resonators for mercuric ion Hg (II) detection in an aqueous environment. The whispering gallery mode (WGM) of the sphere is the surface mode. Therefore, its spectral position shifts in response to the binding of Hg (II) to the sphere surface. In addition, the WGM features very high Q-factor (>10^5). This light circulation effect significantly increases the light interation with the analytes on the sphere surface, resulting in an enhanced sensor sensitivity.

In our experiment, we add Hg(II) to water in which the sensor is immersed. Sensorgram is obtained by monitoring the WGM position in real time. Our experimental results show that a detection limit of 50 ppb (w/w) is achievable when Hg(II) ions bind to the thiol group on the sphere surface with nearly 1:3 stoichiometry. This detection limit can further be improved with 2-mercaptobenzothiazole that binds Hg(II) strongly. Controlled experiments with Zn(II) are also performed, virtually no spectral shift in WGM is observed.