ANALYTICAL CHARACTERIZATION OF MICROLITHOGRAPHICALLY FABRICATED IRIDIUM-BASED ULTRAMICROELECTRODE ARRAYS

The analytical performance of several mercury-coated iridium ultramicr oelectrode arrays (IrUMEAs) was studied using square wave anodic strip ping voltammetry (SWASV) for determination of cadmium in a pH 4.5 acet ate buffer. The microlithographically fabricated IrUMEAs consisted of either 20 or 25 individual disk shaped UMEs, each 10 irm in diameter. The insulating layer utilized in the fabrication process was either si licon dioxide (5000 Angstrom) or silicon nitride (1500 Angstrom or 250 0 Angstrom). Calibration plots demonstrated good linearity for cadmium from 0-100 ppb. Standard deviations, detection limits, and correlatio n coefficients were calculated to determine the stability and reproduc ibility of the IrUMEAs. Repetitive cycles of depositing and stripping Hg at the IrUMEA surface resulted in increased distortion and loss of the SWASV signal. Atomic force microscopy revealed a subtle transforma tion in the IrUMEA surfaces.