Analytica Chimica Acta 532 (2005) 145–151 A glucose biosensor using methyl viologen redox mediator on carbon film electrodes Mariana Emilia Ghica, Christopher M.A. Brett ∗ Departamento de Quimica, Universidade de Coimbra, 3004-535 Coimbra, Portugal Received 19 June 2004; received in revised form 26 October 2004; accepted 26 October 2004 Available online 24 December 2004 Abstract A new methyl viologen-mediated amperometric enzyme electrode sensitive to glucose has been developed using carbon film electrode substrates. Carbon film electrodes from resistors fabricated by pyrolytic deposition of carbon were modified by immobilization of glucose oxidase through cross-linking with glutaraldehyde in the presence of bovine serum albumin. The mediator, methyl viologen, was directly immobilised with the enzyme together with Nafion cation-exchange polymer. The electrochemistry of the glucose oxidase/methyl viologen modified electrode was investigated by cyclic voltammetry and by electrochemical impedance spectroscopy. The biosensor response to glucose was evaluated amperometrically; the detection limit was 20 M, the linear range extended to 1.2 mM and the reproducibility of around 3%. When stored in phosphate buffer at 4 ◦ C and used every day, the sensor showed good stability over more several weeks. © 2004 Elsevier B.V. All rights reserved. Keywords: Glucose; Glucose oxidase; Amperometric enzyme electrode; Carbon film electrode; Methyl viologen mediator; Nafion 1. Introduction Amperometric enzyme electrodes combine the advan- tages of the specificity of the enzyme for recognising particular target molecules with the direct transduction of the rate of reaction into current [1]. Enzyme electrodes, and particularly the glucose electrode, have been subject to numerous studies devoted to their optimisation for both biomedical and bioprocess control applications [2]. For glucose sensors two approaches are commonly employed: (1) monitoring of the hydrogen peroxide produced and (2) measuring the consumption of oxygen. Since, in the case of hydrogen peroxide monitoring the response of the device can be affected by the ambient concentration of oxygen, a solution is to replace the natural electron acceptor of GOx (oxygen) by electroactive compounds that will act as redox mediators [3]. In this case the enzyme glucose oxidase performs the first redox reaction with its substrate, glucose, ∗ Corresponding author. Tel.: +351 239 835295; fax: +351 239 835295 E-mail address: brett@ci.uc.pt (C.M.A. Brett). but is then re-oxidised by the mediator, the reduced mediator in its turn being re-oxidised at the electrode [1]. A good redox mediator for a biosensor has to fulfil char- acteristics such as: (1) an operating potential ideally ∼0V (versus SCE), where oxidation of most electrochemical inter- ferents is avoided; (2) a fast reaction rate with the enzyme; (3) fast electron transfer kinetics; (4) no reaction with oxygen; (5) stable oxidised and reduced forms, etc. Typical mediators investigated have included: ferrocene [4,5] and its derivatives [6,7], Prussian Blue [8,9,10] and other metal hexacyanofer- rates [11,12], quinones [13] and methyl viologen [14–16]. Viologens, derivatives of 4,4 ′ -bipyridine, play an im- portant role as electron relays in systems in which electron transfer is initiated by photochemical or electrochemical processes [17]. They exhibit fast reversible electrochemical response at negative potentials, which makes them useful as redox mediators for numerous enzymatic reactions [15]. Of special significance are the chemical properties of their one- electron-reduction products, which include good stability and the ability to undergo catalysed reactions with protons to give hydrogen [17]. Since viologens are highly water soluble 0003-2670/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2004.10.058