MEMS sensor for detecting mercury at ppb levels

Summary form only given. Sub-surface science research is necessary to assist the Department of Energy (DOE) in solving complex environmental problems associated with hazardous contaminants in soil and groundwater at DOE sites. These contaminants include hazardous metals such as mercury. A novel mercury ion selective electrode has been constructed to have a strongly coordinating macrocyclic ligand binding site covalently attached to a polythiophene film using 1-1,4,10-trioxa-7,13-diazacyclopentadecane-1-thiophenylmethane (TDCD-thiophenylmethane) as a specific chelator. In amperometric mode, the current is proportional to mercury (II) concentrations down to 2 ppb. Reversible cyclic voltammetric waves show that both mercury (I) and mercury (II) are stabilized by the ligand. Monomethyl mercury and vapor phase elemental mercury are also electrochemically determined. Dissolved oxygen and heavy metal cations show no significant interference, even at ten times the Hg concentration. The polymer surface shows robust performance for two years or longer. Fabrication strategies are being developed to optimize probe performance. Variables under study include substrate surface roughness, the ratio of derivatized thiophene (TDCD-thiophenylmethane) to underivatized thiophene in the surface polymer, ratio of thiophene with two chelating rings to thiophene with only one, number and thickness of electrodeposited polymer layers, composition of polymer layers, and number of -CH₂- units separating the chelating ring from the thiophene monomer units. The probe exhibits linear response to Hg concentration, and detects Hg in several forms