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 recently shown to adsorb in close to monolayer coverage and well-defined stable orientations on alkanethiol monolayers self-assembled on Au(111)-surfaces. Adsorption is caused by hydrophobic interactions between the alkanethiol and the hydrophobic protein surface around the copper centre, orienting the latter towards the electrode surface in a way favourable for electron exchange. In this report we show that similar stable adsorption of functional azurin on polycrystalline electrodes can be achieved, represented by azurin adsorption on a decanethiol monolayer. This facilitates significantly the use of this approach to protein immobilization. Reversible monolayer voltammetry is observed for scan rates up to about 1 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)-electrodes. The sensitivity of azurin monolayer voltammetry on self-assembled alkanethiols to hydrophobic interactions was also used to address possible voltammetric differences between native and recombinant azurin. Voltammetric patterns, equilibrium reduction potentials, and electrochemical rate constants were, however, indistinguishable for the two proteins.