Fabrication of boron-doped diamond ultramicroelectrodes for use in scanning electrochemical microscopy experiments.

Boron-doped diamond (BDD) ultramicroelectrode (UME) tips were fabricated by the growth of BDD films by chemical vapor deposition onto sharpened tungsten wires. Both nanocrystalline and microcrystalline forms of diamond coatings were examined. The diamond-coated wires were selectively insulated with nail varnish, electrophoretic paint, or fast-setting epoxy to form UME tips of critical dimensions of 1-25 microm. The geometry of the exposed electrode area was disk or hemispherical in most cases. Cyclic voltammetry and chronoamperometry were used to assess exposed electrode area and integrity of the insulation. BDD UMEs were used to obtain SECM approach curves to an insulating and a conducting substrate, which were fitted to the theory appropriate for the observed tip geometry. The tips were used to obtain SECM images of immobilized respiring E. coli, illustrating the suitability of BDD UMEs for electrochemical imaging in biological media.