Gold Nanoparticles as Electronic Bridges for Laccase-Based Biocathodes

Direct electron transfer (DET) reactions between redox enzymes and electrodes can be maximized by oriented immobilization of the enzyme molecules onto an electroactive surface modified with functionalized gold nanoparticles (AuNPs). Here, we present such strategy for obtaining a DET-based laccase (Lc) cathode for O-2 electro-reduction at low overpotentials. The stable nanostructured enzymatic electrode is based on the step-by-step covalent attachment of AuNPs and Lc molecules to porous graphite electrodes using the diazonium salt reduction strategy. Oriented immobilization of the enzyme molecules on adequately functionalized AuNPs allows establishing very fast DET with the electrode via their Cu T1 site. The measured electrocatalytic waves of O-2 reduction can be deconvoluted into two contributions. The one at lower overpotentials corresponds to immobilized Lc molecules that are efficiently wired by the AuNPs with a heterogeneous electron transfer rate constant k(0) >> 400 s(-1).