Voltammetry of native and recombinant Pseudomonas aeruginosa azurin on polycrystalline Au- and single-crystal Au(111)-surfaces modified by decanethiol monolayers

The native blue single-copper protein azurin (Pseudomonas aeruginosa) was r ecently shown to adsorb in close to monolayer coverage and well-defined sta ble orientations on alkanethiol monolayers self-assembled on Au(111)-surfac es. Adsorption is caused by hydrophobic interactions between the alkanethio l and the hydrophobic protein surface around the copper centre, orienting t he latter towards the electrode surface in a way favourable for electron ex change. In this report we show that similar stable adsorption of functional azurin on polycrystalline electrodes can be achieved, represented by azuri n adsorption on a decanethiol monolayer. This facilitates significantly the use of this approach to protein immobilization. Reversible monolayer volta mmetry is observed for scan rates up to about I V s(-1). The peaks separate at higher rates. Equilibrium potentials and interfacial electron transfer rate constants are indistinguishable from those at single-crystal Au(111)-e lectrodes. The sensitivity of azurin monolayer voltammetry on self-assemble d alkanethiols to hydrophobic interactions was also used to address possibl e voltammetric differences between native and recombinant azurin. Voltammet ric patterns, equilibrium reduction potentials, and electrochemical rate co nstants were, however, indistinguishable for the two proteins. (C) 2001 Els evier Science B.V. All rights reserved.