Mercury ion sensing by film-bulk-acoustic-resonator mass sensor

This paper describes an FBAR (film bulk acoustic resonator) mass sensor for detecting Hg in liquid. With a thin Au film deposited on the surface of an FBAR, the FBAR's resonant frequency shifts as Hg amalgamates on the Au surface. The FBAR sensor is measured to be capable of detecting a concentration of 10/sup -19/ M Hg/sup 2/ (i.e., 0.2 ppb Hg/sup 21/). Other cations such as K/sup 1/, Ca/sup 2/, Mg/sup 2/, Zn/sup 21/, Ni/sup 2/ have shown to have little or no effect on the resonant frequency of the FBAR. Responses of the FBAR sensors coated with various thicknesses of Au film to a same concentration of Hg/sup 2/ have been compared. Finally, an FBAR with a thiol-compound-modified Au film is shown to have a smaller frequency shift than that with a pure Au film.