M. Schweyer et al., ELECTROCHEMICAL PIEZOELECTRIC SENSORS FOR TRACE IONIC CONTAMINANTS, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 45(5), 1998, pp. 1408-1415
Industrial processes, such as fossil fuel combustion and nuclear mater
ials processing, have resulted in heavy metal contamination of soils a
nd potentially of the surrounding groundwater. In particular, mercury
contamination of groundwater is a serious threat to the ecosystem, cum
ulating in serious health problems for humans as well as wildlife. Mon
itoring of mercury contamination in groundwater requires a method of l
ong-term verification. Sensors with lifetimes of months to years of op
eration without operator intervention are required. One sensor geometr
y, which is capable of detecting relevant concentrations of aqueous io
nic contaminants, such as mercury, while withstanding typical environm
ental conditions, is the shear horizontal acoustic plate mode (SHAPM)
sensor. This sensor protects the electronics from the potentially corr
osive aqueous fluid environment while providing a significant interact
ion with the fluid. Gold films are employed to accumulate the mercury
via surface amalgamation. The added mass is measured as a change in th
e resonant frequency of the piezoelectric sensing element. Electrochem
ical techniques are employed to impart reversibility and to accelerate
response kinetics. Results indicate a sensitivity of approximately 2.
4 ng/mL, which approaches the 2.0 ng/mL limit imposed by the Safe Drin
king Water Act (SDWA).