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.