SCANNING ELECTROCHEMICAL MICROSCOPY .19. ION-SELECTIVE POTENTIOMETRIC MICROSCOPY

Potentiometric pH selective tips for scanning electrochemical microscopy (SECM) have been developed and used to image local pH changes in a variety of model chemical systems. Images of pH profiles around a platinum microelectrode during water reduction, a corroding disk of silver iodide in aqueous potassium cyanide, a disk of immobilized urease hydrolyzing urea, and a disk of immobilized yeast cells in glucose solution were obtained. A simple method for fabricating antimony microdisk electrodes suitable for use in SECM is described. The general theory for SECM with potentiometric ion selective tips is also presented, assuming that the tip is a purely passive sensor. Reasonable agreement with theory was observed for relatively large tip to surface separations. The deviations observed at small separations were due to shielding of the surface by the tip and, consequently, were found to be much less significant for smaller tips.