Bioelectrocatalytic reduction of oxygen at gold nanoparticles modified with laccase

To characterise bioelectrocatalytic oxygen reduction at gold nanoparticles (AuNPs) modified with Trametes hirsuta laccase (ThLc) combined electrochemical and quartz crystal microbalance measurements have been used. The electrodes with different degrees of AuNP-monolayer coverage, θ, have been studied. In every case of θ close to theoretically possible 44 ThLc molecules adsorbed at 22nm diameter AuNP. The bioelectrocatalytic current was recalculated down to the current at a single AuNP. Unexpectedly, the current at a single AuNP was higher when θ was higher. The maximum current reached at a single AuNP was 31·10(-18)A which corresponds to the enzyme turnover (kcat) 13s(-1). This rate is lower than the homogeneous ThLc turnover (190s(-1)) suggesting partial denaturation of ThLc upon adsorption or that some ThLc are not in DET contact with the electrode surface.