An acoustic plate mode sensor for aqueous mercury

Many industrial processes have resulted in mercury contamination of soils and potentially of the surrounding groundwater. The remediation efforts for these sites requires a method of long-term verification. Sensors with lifetimes of months to years of operation without operator intervention are required to monitor these sites. One sensor geometry which is capable of detecting relevant concentrations of aqueous mercury while withstanding typical environmental conditions is the acoustic plate mode (APM) microsensor. This piezoelectric sensor protects the electronics from the potentially corrosive aqueous fluid environment while providing a significant interaction with the fluid. Gold films are employed to accumulate the mercury via surface amalgamation. The added mass is measured as a change in the resonant frequency of the piezoelectric element. A reference device helps compensate environmental factors, such as temperature drift, solution effects (viscosity, density and conductivity changes) and pressure fluctuations. Initial results indicate a sensitivity of approximately 10 ng/ml (10 /spl mu/g/L) which is approximately five times the limit imposed by the safe drinking water act (SDWA). Research is currently underway to lower this detection limit to allow the sensor to meet the requirements of environmental sensing, wastewater monitoring and drinking water testing.