Fabrication of glass-coated electrodes with nano- and micrometer size by means of dissolution with HF

Platinum nano-electrodes were fabricated at the success rate 76% by the six processes; (i) etching a Pt wire in ethanol-water mixture, (ii) sealing it with a glass sheath, (iii) grinding roughly the glass tip, (iv) polishing the tip while monitoring the capacitive ac current flowing through the glass thin film on the Pt, (v) dissolving the glass film in HF solution until a part of Pt was exposed, and (vi) heating the tip at 85 °C for stabilization. A key of the process was to make a thin glass film on the Pt tip (iv) and to expose the Pt surface chemically by (v). 50 electrodes thus fabricated had diameters ranging from 1 nm to 5 μm, estimated from the steady-state diffusion-controlled current of ferrocene in acetonitrile and ferrocenyl derivative in aqueous solution. They exhibited reproducible and stable voltammograms without hysteresis, withstanding 6 hours’ continuous use and 15 hours’ iterative processes of heat and voltammetry. Not only the halfwave potentials but also slopes of the log-plots were independent of radii of the electrodes. No kinetic effect was revealed in the steady-state voltammograms.