Analysis of heavy-metal ions using mercury microelectrodes and a solid-state reference electrode on a Si wafer

Micro working electrodes and a solid-state reference electrode have been fabricated using semiconductor processes for electrochemical detection of heavy-metal ions in aqueous media. The working electrodes are mercury-coated platinum microelectrodes 5 μm, 10 μm and 25 μm in diameter. The smaller electrode shows the higher sensitivity and the detection limits of the 5-μm-diameter electrodes are about 0.2 ppb and 0.4 ppb for cadmium and lead ions, respectively. The reference electrode is a Ag/AgCl electrode coated by polyvinyl chloride (PVC)/Nafion layer containing Cl^- ions. The potential variation of the fabricated solid-state reference electrodes is about 55 mV under a 0.1 M Cl^- concentration.