Fabrication and characterization of conical microelectrode probes templated by selectively etched optical fibers for scanning electrochemical microscopy

Selectively etched optical fibers were used as a new template material of conical ultramicroelectrodes, which are suitable for use as a probe in scanning electrochemical microscopy (SECM). Multistep index optical fibers with high-GeO₂-doped core surrounded by two cladding layers were etched in a NH₄F/HF solution for reproducible construction of tapered optical fibers with well-defined tip geometry. The etched fibers were coated with a thin gold layer by sputtering and then insulated by deposition of electrophoretic paint. The size and shape of the electrodes exposed at the end of the tips were determined by steady-state cyclic voltammetry and SECM. The SECM tip current-distance (approach) curves over conductive and insulating substrates agree with the theoretical curves obtained by numerical simulations, confirming the conical electrode geometry as observed by scanning electron microscopy. The analysis gave values in the range of 0.44-1.0 and 0.53-1.2 μm for the base radius and height of the conical tips.