Poly(brilliant cresyl blue) modified glassy carbon electrodes: Electrosynthesis, characterisation and application in biosensors Mariana Emilia Ghica, Christopher M.A. Brett * Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, 3004-535 Coimbra, Portugal article info Article history: Received 9 October 2008 Received in revised form 7 January 2009 Accepted 20 January 2009 Available online 24 January 2009 Keywords: Phenoxazine dye Brilliant cresyl blue Electropolymerisation Glassy carbon Redox mediator Glucose oxidase abstract The phenoxazine dye, brilliant cresyl blue (BCB) has been polymerised on glassy carbon electrodes by potential cycling, and the resulting poly(brilliant cresyl blue) (PBCB) film has been studied by cyclic vol- tammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. A differential pulse voltammetry study in different supporting electrolytes with different pH values revealed that the current intensity of the oxidation peak of the resulting polymer increases with increase in pH up to pH 4.1 where the highest response is exhibited and then begins to decrease. It was also observed that the peak potential moves to more negative values with increase in pH with a slope of 51 mV/pH, indi- cating an equal number of electrons and protons in the redox process. The electrode modified with poly(brilliant cresyl blue) was successfully applied to the determination of hydrogen peroxide in amper- ometric mode at 0.0 V vs. SCE. Glucose oxidase enzyme was then immobilised by crosslinking with glu- taraldehyde and bovine serum albumin (BSA): the polymer functions as a redox mediator in a glucose biosensor allowing determination of glucose at small negative potentials with low interferences. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Since the discovery of the formation of polymer semiconductor films by the electrochemical oxidation of pyrrole [1] and aniline [2], the interest in electrogenerated polymers has been continuously growing. Conducting polymers are very attractive due to their po- tential use as electrochromic devices, capacitors, gas separation membranes, anti-static membranes, catalysts and electromagnetic shielding devices. However, when used together with proteins and enzymes the result is not always so encouraging due to the low cat- alytic current obtained [3]. In order to overcome this inconvenience, one can prepare conducting films by electropolymerisation from a monomer which is itself a redox-active compound. In this way azine dyes have proved to be very interesting compounds due to their ability to act as electron donors/acceptors in enzyme reactions and, simultaneously, such dyes are able to undergo electropolymer- isation. Among these dyes, several phenazines, phenothiazines and phenoxazines have been polymerised on different electrodes and have been used as redox mediators mainly with NAD-dependent dehydrogenases [4,5] and also with oxidase enzymes [6,7]. Brilliant cresyl blue (BCB) is a cationic quinine-imide dye with a planar and rigid structure as shown in Scheme 1a and has been proven to posses promising properties as a redox catalyst. Brilliant cresyl blue has been used as a fluorescent indicator for measure- ments across biological membranes [8]. It can react with heparin which permits its determination by UV–Vis spectrophotometry and linear sweep voltammetry [9], and interacts with dsDNA by both electrostatic attraction and intercalation thus permitting detection of natural DNA damage [10]. BCB can adsorb strongly on electrode surfaces and these chemically modified electrodes have been used for the determination of NADH [11] and to study the redox behaviour of haemoglobin [12]. BCB was also used for the determination of oxalate [13], formaldehyde [14], nitrite [15], protein [16], hydrazine [17] and cyclodextrin [18] using spectro- photometric detection. Another application was as mediator in electrochemical biosensors [19,20]. However, the electrochemical behaviour of BCB has been investigated only by using polarography [21] or transparent thin layer spectroelectrochemistry [22] and re- ports concerning the electropolymerisation of BCB are just two to our knowledge [23,24] with only brief characterisation. We have previously reported on the polymerisation of the phenazine dye neutral red (NR) [7,32] and the phenothiazines methylene blue (MB) and methylene green (MG) [29], the charac- terisation of the resulting polymers and their potential use as re- dox mediators. In this context of studying azine dyes, the present work focuses on the electrochemical synthesis of poly(brilliant cre- syl blue), from the phenoxazine brilliant cresyl blue, optimisation of the polymerisation conditions and study of the electrochemical properties of the resulting redox polymer as well as possible appli- cation as redox mediator in enzymatic sensors. BCB was electro- polymerised on glassy carbon electrodes. The PBCB polymer- modified electrode was found to possess high stability and was characterised by cyclic voltammetry, differential pulse voltamme- 0022-0728/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2009.01.019 * Corresponding author. Tel./fax: +351 239835295. E-mail address: brett@ci.uc.pt (C.M.A. Brett). Journal of Electroanalytical Chemistry 629 (2009) 35–42 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem