Mercuric Ion Sensing by a Film Bulk Acoustic Resonator

This paper describes a film bulk acoustic resonator (FBAR) mass sensor for detecting Hg²⁺ ion in water with excellent sensitivity and selectivity. When a thin Au film was deposited on the surface of an FBAR, the resonant frequency shifted to a lower value when the film was exposed to Hg²⁺ in aqueous solution. The FBAR sensor detected as low as 10^-9 M Hg²⁺ (0.2 ppb Hg²⁺) in water. Other ions such as K⁺, Ca²⁺, Mg²⁺, Zn²⁺, and Ni²⁺ had little or no effect on the resonant frequency of the FBAR. Coating of the FBAR Au surface with a self-assembled monolayer (SAM) of 4-mercaptobenzoic acid decreased the Hg²⁺ response.