Ž . Bioelectrochemistry and Bioenergetics 47 1998 39–46 Electrochemical behaviour of FAD and FMN immobilised on TiO 2 modified carbon fibres supported by ATR-IR spectroscopy of FMN on TiO 2 L.T. Kubota a , L. Gorton b, ) , A. Roddick-Lanzilotta c , A.J. McQuillan c a Institute of Chemistry, Unicamp, P.O. Box 6154, 13083-970, Campinas, SP, Brazil b Department of Analytical Chemistry, UniÕersity of Lund, P.O. Box 124, S-221 00, Lund, Sweden c Department of Chemistry, UniÕersity of Otago, P.O. Box 56, Dunedin, New Zealand Received 17 July 1998; accepted 11 September 1998 Abstract Carbon fibre electrodes were modified with titanium oxide and used to adsorb some flavins on the electrode surface. FAD and FMN Ž X . strongly adsorbed on the titanium oxide dispersed on carbon fibres and remained stable for at least 2 months. The formal potential E8 at pH 7.0 of adsorbed FAD and FMN were y245 and y250 mV vs. SCE, respectively. The shift of the E8 X of about 200 mV towards more positive values at pH 7.0 compared with that of the dissolved flavin was assigned to the interaction between titanium oxide and the flavins. The variation of the E8 X with pH between 1 and 8 was also very much less than for dissolved flavins. The adsorbed flavins showed a good electrocatalytic activity for NADH oxidation in aqueous solution applying a potential of 0 mV vs. SCE. The stability of the electrode was very good and no significant change in either surface coverage of FMN or FAD or electrocatalytic response for NADH oxidation was observed after 250 cycles. A linear response range for NADH between 1 and 6 mM was obtained. Additionally, attenuated total reflectance IR-spectra of FMN adsorbed on titanium films were recorded to clarify the interaction between the flavin and the support. q 1998 Elsevier Science S.A. All rights reserved. Keywords: Electrocatalysis; NADH; Chemically modified electrode; Flavin; Attenuated total reflectance IR spectroscopy 1. Introduction Electrode modification is a subject of intensive investi- w x gations 1–3 since it may turn out to be a good alternative to develop new analytical tools to be able to analyse w x complex samples 4,5 . Surface modifications of carbon fibre electrodes can yield electrodes for use in small w x volume samples and for in situ determinations 6–8 . Several papers have been published about carbon fibre w x modifications 9,10 , however, the immobilisation of any flavin on these kind of materials has not been studied yet. The electron transfer between NADH and flavoproteins is w x essential in all biological organisms 11,12 . Therefore, investigations of model reactions between NADH and its analogues and flavins have been the subject of many w x investigations 13 . Thus, studies of immobilised flavin on carbon fibre surfaces can be very important to shed further ) Corresponding author. light on the electrochemistry of the modifier as well as for new possible use of such electrodes for sensing many biological compounds. The small size of carbon fibres and the possibility to immobilise electron mediators could be ideal for the development of sensors for in situ determina- wx tion 7 . w x In a previous work 14 , the modifications of carbon fibre electrodes with titanium oxide was described. The electroactivity of this modified carbon fibre is increased and a much more reversible electron transfer was observed for hexacyanoferrate. The possibility to immobilise new compounds on the carbon fibre electrode due to the Lewis w x acid site of the titanium oxide 15 is also an important aspect to be used for interaction with possible modifiers having basic amino or phosphate groups. Flavins present these two groups which can be useful to interact with titanium oxide in acid media, since the zero charge point w x for titanium oxide is about 6.5 16 . In this work, the immobilisation of FAD and FMN on titanium oxide modified carbon fibre is described as well 0302-4598r98r$ - see front matter q 1998 Elsevier Science S.A. All rights reserved. Ž . PII: S0302-4598 98 00182-2