Mercuric Ion Sensing by a Film Bulk Acoustic Resonator

This paper describes a film bulk acoustic resonator (FBAR) mass sensor for detecting Hg
²⁺
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 Hg
²⁺
in aqueous solution. The FBAR sensor detected as low as 10
^-9
M Hg
²⁺
(0.2 ppb Hg
²⁺
) in water. Other ions such as K
⁺
, Ca
²⁺
, Mg
²⁺
, Zn
²⁺
, and Ni
²⁺
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 Hg
²⁺
response.