NANOMETER-SIZED ELECTROCHEMICAL SENSORS

Nanometer-sized glass-sealed metal ultramicroelectrodes (UMEs) have be en prepared using a laser-based micropipet puller. The tip was exposed to solution either by etching away a small portion of glass insulator or by micropolishing. The characterization of the UMEs was carried ou t by a combination of steady-state voltammetry, scanning electron micr oscopy (SEM), and scanning electrochemical microscopy (SECM). The cycl ic voltammograms obtained have a regular shape with very small capacit ive and resistive background. The effective electrode radii obtained f rom voltammetry were between 2 and 500 mn. From the SEM micrographs, t he shape of polished tips appears to be close to a microdisk, while th e geometry of etched electrodes is closer to conical. Accordingly, the SECM current-distance curves (i(T)-d) obtained with polished electrod es fit well the theory for a disk-shaped tip, while a 20-nm-radius etc hed electrode was shown to be a fairly sharp cone with a height-to-rad ius ratio of about 2.5. The experimental data were compared to the the ory developed for disk-shaped, conical, and recessed tips to demonstra te suitability of the produced electrodes for quantitative electrochem ical experiments. The prospects of steady-state measurements of the ra tes of fast heterogeneous reactions are discussed. Submicrometer-sized ion selective electrodes (ISEs) were prepared by coating etched Ag ti ps with silver iodide. The concentration response of such ISEs remaine d stable and linear after coating of the ISEs with protective Nafion f ilm.