Surface and Electrochemical Studies of Thin Film Diamond
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0956-J15-02
Surface and Electrochemical Studies of Thin Film Diamond John Foord and David Opperman Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford, OX1 3TA, United Kingdom
ABSTRACT The behavior of diamond electrodes for electrochemical applications in aqueous media containing the protein bovine serum albumin has been explored, to examine the degree of electrode poisoning which occurs. Although the diamond electrode retains good activity in such solutions, electrode fouling is found at long contact times due to protein adsorption. Two adsorption processes are observed. The first is a simple physical adsorption mechanism, and can be simply reversed by washing the electrode in water. The second mechanism is only observed when negative potentials are applied to the diamond electrode and is attributed to the attraction and reaction of the positively charged protein at the electrode interface. Electrode poisoning is also observed in the presence of power ultrasound, although the electrochemical signals are usefully enhanced under these conditions due to enhanced mass transport to the electrode surface.
INTRODUCTION Boron-doped diamond is now an established electrode material for electrochemistry, on account of a range of advantageous properties displayed, including chemical inertness, a resistance to electrode fouling, low background currents and a wide working potential window [1]. Applications range from bulk electrochemical decontamination of chemical waste to electrosynthesis and electrochemical sensing. The resistance to electrode fouling is of particular interest in biological media, where adsorption on the electrode is a frequent cause of electrode failure, and is driving, for example, our development of diamond “tips” for scanning electrochemical microscopy applications in such media [2]. However, there have been few studies which have tried to quantify the extent to which fouling occurs at diamond electrodes. The purpose of the present paper is therefore to study this in greater detail, by examining the interaction of diamond electrodes with protein solutions. The protein selected fro study in the present case in bovine serum albumin (BSA), which has a molecular weight of around 66, 000 and an isoelectric point of 5. This protein is often used to assess protein adsorption phenomena, and it is for example known that 1 gL-1 solutions typically reduce the activity of glassy carbon electrodes by up to 60% [3]. We compare this with the behavior of diamond electrodes in the present study, and also examine the extent to which ultrasound can be used to reduce the fouling observed [4].
EXPERIMENTAL The boron-doped diamond electrode used was in the form of a polished disc of diameter 3mm encapsulated in a PTFE insulating sheath, as supplied by Windsor Scientific (UK). Voltammetric measurements employed an Ecochemie µ-Autolab II potentiostat running GPES software and a standard three-electrode arrangement in a single pot, utilizing a calomel reference electrode and a
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