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^-19 M Hg² (i.e., 0.2 ppb Hg²¹). Other cations such as K¹, Ca² , Mg², Zn²¹, Ni² 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 Hg² 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