Pyrolytic carbon microelectrodes

FIG. 11 Top Schematic diagram of the capillary carbonization setup. Bottom Schematic picture of the pyrolytic carbon microelectrode made from pulled quartz capillaries using this setup. 

FIG. 12 Cyclic voltammogram of a pyrolytic carbon microelectrode in a 5 mM aqueous solution of hexaamineruthenium(III) chloride and 1 M KC1 electrolyte, (a) Scan rate 0.1 V/s. (b) Scan rate 10 V/s. 

FIG. 13 Experimental approach curve obtained with a 0.4 /xm apparent diameter pyrolytic carbon microelectrode in a 5 mM aqueous solution of hexaamineruthen-ium(III) chloride and 1 M KC1 electrolyte. The substrate is a 100 /xm platinum disk. (Upper dashed curve) Theoretical positive feedback approach curve. (Lower dashed curve) Theoretical negative feedback approach curve. (Inset) Schematic picture of the very end of the carbonized capillary compatible with the experimental approach... 

M.F. Suaud-Chagny and F.G. Gonon, Immobilization of lactate dehydrogenase on a pyrolytic carbon fiber microelectrode. Anal. Chem. 58, 412—415 (1986). 

Suaud-Chagny and Goup (1986) immobilized LDH on a pyrolytic carbon fiber microelectrode by impregnation in an inert protein sheath that was first electrochemically deposited around the active tip of the electrode. The NADH detection was improved by electrochemical treatment of the electrode. The detection limit for pyruvate was lower than 1 pmolA. The sensor was used to estimate pyruvate concentration in rat cerebrospinal fluid. 

In the last 10 years, a lot of work has been done on the design of carbon microelectrodes, and several reviews have been devoted to this large amount of work (for reviews see Refs. 32 and 33). The purpose of this section is therefore only to review the techniques useful for the preparation of SECM tips based on the criteria presented earlier defining a good SECM tip. Some of our own work about the use of pyrolytic carbon electrodes as SECM probes will also be discussed. 

The use of pyrolytic carbon deposited as a thin film resulting from the pyrolysis of methane as an electrode material has been reported by Blaedel and Mabbot [50]. The pyrolysis of methane on a heated quartz cylinder under an inert atmosphere resulted in the deposition of a carbon film onto the quartz cylinder. The reasonably good electrochemical behavior of this pyrolytic carbon film was demonstrated. This technique was later applied for the deposition of carbon inside heated quartz capillaries. At first, the deposition of a thin carbon film on the inside walls of micrometer-sized capillaries was reported [51]. In order to be usable, the capillary had then to be backfilled with epoxy glue and cut with a razor blade. This procedure resulted in ring-shaped carbon microelectrodes of a few microns in size. More recently, it was reported that this technique could also result in diskshaped carbon microelectrodes if the carbonization time was increased, and the end of the capillary was then supposedly ultimately closed by a carbon cap [52]. The resulting electrodes displayed, at least at slow scan rates reported, a remarkably good electrochemical behavior, both in water and... 

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