Resonant MEMS sensors for detection of aqueous heavy metal ions with Sub-ppm resolution

This work presents a new approach for detection of trace amounts of heavy metal ions in water samples using capacitive silicon resonators as ultra-sensitive mass sensors. This approach is based on reduction of metal ions by the silicon in a resonant structure and consequently deposition of a very thin metal layer on the resonator surface changing its resonant frequency. Preliminary measurements demonstrate successful detection of sub-ppm concentrations of copper(II) ions in water. Relatively large frequency shifts (hundreds of ppm) have been measured for resonators exposed to copper concentrations as low as 4 muM (0.26 ppm). This corresponds to a few atomic layers of copper (~5 Aring thick) deposited on the resonator surface.