Cathophoresis paint insulated carbon fibre ultramicro disc electrode and its application to in vivo amperometric monitoring of quantal secretion fromsingle rat melanotrophs

This paper reports the preparation and characterization of carbon fibre ult ramicro disc electrodes (CUMDEs) by employing cathodic electrophoresis pain t to electrically and chemically insulate a carbon fibre protruding from a pulled glass capillary housing. A thin and uniform paint coating was deposi ted electrochemically onto a carbon fibre of 7 mu m in diameter, and then h eat cured. The film thickness and its resistivity can be controlled by vary ing parameters such as the cathodic deposition voltage, the curing temperat ure, etc. Then, the coated carbon fibre was cut to expose a disc-shaped ele ctrode surface with an overall tip diameter of about 12 mu m. The electrode s were examined by optical and scanning electron microscopy and their elect rochemical behaviour and properties were characterized using cyclic voltamm etry, amperometry and electrochemical impedance spectroscopy. Cyclic voltam mograms of hexacyanoferrate(III) in aqueous and of ferrocene in acetonitril e media displayed low-noise, low-background sigmoidal responses with virtua lly no current hysteresis. The high performance of the proposed cathophores is paint insulated CUMDEs was verified successfully by carrying out in vivo amperometric monitoring of the secretory activity of stimulated single rat melanotrophs. The extremely low current noise (1-2 pA rms) and high tempor al resolution ensure the suitability of the proposed electrode for studying peptide hormone release at a single cell level. (C) 1999 Elsevier Science B.V. All rights reserved.