ELSEVIER Analytica Chimica Acta 303 (1995) 275-283 ANALYTICA CHIMICA ACTA Properties of carbon fibre microelectrodes as a basis biosensors for enzyme L.I. Netchiporouk a, * , A.A. Shul’ga b, N. Jaffrezic-Renault ‘, C. R. Olier ‘, R. Cespuglio d Martelet ‘, a Sector ofBioelectronics, Kiev Uniuersiry, P.O. Box 152, Kiev: 252001, Ukraine b Institut fir Chemo- und Biosensorik, I1 Mendelstrasse, D-4400 Miinster, Germany ’ Cedex LPCI URA CNRS 404, Ecole Centrale de Lyon, B.P. 163, 69131 Ecully, France ’ Department of Experimental Medicine, Claude Bernard Unil’ersity, 8 Av. Rockefeller, F-69373 Lyon, France Received 9 February 1994; revised 3 October 1994; accepted 19 October 1994 Abstract The electrochemical properties of carbon fibre microelectrodes (CFMES) are investigated in view of their application for the construction of amperometric biosensors based on oxidase enzymes. Scanning electron microscopy and cyclic voltammetry studies show that an appropriate electrochemical pretreatment has a strong effect on both morphology and electrochemical behaviour of the carbon fibre surface for all tested types of fibres. For AGT/F 10000 carbon fibres chosen for further study the surface becomes very smooth and a half-wave potential for H,O, oxidation assumes a reproducible value of about of +0.8 V vs. SCE. The electrochemistry of the ferro/ferricyanide redox system is irreversible and quasi-reversible on unpretreated and pretreated electrodes, respectively. In the latter case, however, the addition of 20 mM MgCl, or CaCl, to the buffer solution makes the cyclic voltammetry curves reversible. Using glucose oxidase as a model enzyme, a glucose microbiosensor is prepared by enzyme cross-linking onto the carbon fibre surface in glutaraldehyde vapour. When operating in a H,O, detection mode the biosensor dynamic range extends only up to about 2 mM glucose. The deposition of additional membranes (a reticulated bovine serum albumin and Nafion film) on top of the enzyme layer allows an extension of the dynamic range up to 13 mM and substantial elimination of interferences. When ferricyanide is used as a soluble mediator the biosensor dynamic range extends up to 100 mM glucose. The biosensor response was stable at least for one month when it was stored in air or in a phosphate buffer (pH 7.4) at 4°C and used for about 30 measurements. Keywords: Biosensors; Glucose oxidase; Glucose; Surface morphology; Carbon fibres 1. Introduction Much of the current work in the analytical field is devoted to the miniaturisation of the analytical * Corresponding author. equipment. One particular area is the development of microelectrodes with their possible use as a basis for microbiosensors in microflow systems and for in vivo studies, especially for in vivo brain research. The application of carbon fibre microelectrodes (CFMES) for an electrochemical determination of neurotransmitters [l] has attracted a great interest to this powerful tool of analytical investigations. 0003-2670/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0003-2670(94)00538-9