Please cite this article in press as: E.M. Pinto, et al., Electrochim. Acta (2008), doi:10.1016/j.electacta.2008.01.096 ARTICLE IN PRESS +Model EA-13368; No. of Pages 7 Available online at www.sciencedirect.com Electrochimica Acta xxx (2008) xxx–xxx Interaction of BSA protein with copper evaluated by electrochemical impedance spectroscopy and quartz crystal microbalance Edilson M. Pinto a,b , David M. Soares b , Christopher M.A. Brett a,∗ a Departamento de Qu´ ımica, Faculdade de Ciˆ encias e Tecnologia, Universidade de Coimbra, 3004-535 Coimbra, Portugal b Instituto de F´ ısica Gleb Wataghin, Unicamp, CP 6165 Campinas SP, Brazil Received 1 August 2007; received in revised form 25 January 2008; accepted 31 January 2008 Abstract The interaction of bovine serum albumin (BSA) protein with copper in phosphate buffer solution has been studied by a combination of electrochemical impedance spectroscopy (EIS) close to the open circuit potential, with simultaneous monitoring by the electrochemical quartz crystal microbalance (EQCM), in order to throw light on BSA adsorption. Copper films were electroplated onto gold quartz crystals and mounted in the EQCM. Experiments were conducted in the presence and absence of dissolved oxygen and of BSA and the results show the influence of O 2 on the protein/metal interaction and also show specific interactions between BSA and copper. The good reproducibility obtained in these experiments suggests future application to other systems and which should lead to a better understanding of the use of such types of protein as corrosion inhibitors. © 2008 Elsevier Ltd. All rights reserved. Keywords: Electrochemical quartz crystal microbalance; Electrochemical impedance spectroscopy; Bovine serum albumin; Copper 1. Introduction As a model protein, bovine serum albumin (BSA) has been employed in a number of research studies concerning the adsorp- tion on and interaction of proteins with different electrode materials. A number of papers have reported the application of the electrochemical QCM (EQCM), usually together with voltammetry, electrochemical impedance spectroscopy (EIS) or surface analysis techniques [1–8]. The development and application of the quartz crystal microbalance (QCM) has grown in many fields of science, and recently new materials such as diamond-like carbon films, poly- meric films and nanostructured films have been investigated [9–11]. The QCM has also been used in thin-film deposition monitors and in gas sorption and vapour sensors using care- fully selected coating materials as the chemically active interface [12,13]. Within a certain range, the resonant frequency shift, f q , is sufficiently linear with the added loading mass, m, to be independent of the film’s other properties as a material, and the ∗ Corresponding author. Tel.: +351 239 835295; fax: +351 239 835295. E-mail address: brett@ci.uc.pt (C.M.A. Brett). sensitivity, f q /m, is proportional to f 2 q [14]. In cases where the thin film coating serves simultaneously as an electrode, this proportionality can be useful for correlating charge transfer and mass transfer occurring at electrode–solution interfaces. EQCM studies have been carried out together simultaneously with double-layer capacitance measurements to investigate the adsorption of BSA on gold [1]. The adsorption of insulin on platinum was studied by simultaneous cyclic voltamme- try and EQCM measurements and by EIS [2]. The adsorption of BSA on gold and platinum was probed by simultaneous EIS and QCM measurements in Britton-Robinson buffer with the ferri/ferrocyanide couple as redox probe [3]; it was found that BSA adsorption successfully inhibits gold corrosion dur- ing the oxidation of hexacyanoferrate (II). In a different type of investigation, the surfaces of gold electrodes, covered with self- assembled monolayers of PEGylated thiols to prevent adsorption of proteins, were monitored by EIS and QCM measurements, and this approach was found to be wholly successful for resist- ing BSA adsorption [4]. The influence of BSA on titanium oxide passivation phenomena has been demonstrated [5], and its adsorption on an iron–chromium alloy in acid solution [6] and on passivated chromium [7,8] have very recently been investi- gated. For passivated chromium [7,8], in situ flow-cell EQCM 0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2008.01.096