Direct electrochemistry and enzyme-involved photo-electrocatalysis of oxygen reduction for the electrode on the basis of titanium dioxide-graphene oxide nano-complex with laccase accommodation

Abstract

Nano-complex consisting of Titanium dioxide and graphene oxide via covalent bonding was proposed to be Laccase immobilization matrix through collaborative effect of chemical tethering and adjacent complexation between TiO2 and Laccase molecule. Geometrical feature, structural characteristics and physio-chemical properties of nano-composite with Laccase entrapment were systematically characterized and evaluated. Influences of mutual interactions between element of nano-complex and incorporated protein molecule on kinetics of electro-catalysis and efficiency of photo-electrocatalysis for oxygen reduction of Laccase based electrode were quantitatively analyzed. Results from measurements indicated mutual interactions dominated by adjoining ligation would lead to irregular arrangement of protein molecules on the surface of enzyme carrier and decrease the orderliness of nano-complex with Laccase anchoring with improved hydrophilicity. The combination of Laccase with P25 in nano-complex via the static quenching would enhance the utilization efficiency of external illumination with the crippled band gap (Eg) in the indirect mode (∼1.43 eV for nano-composite with Lac integration). Such combination would alter the route of charge transferring which meant the redox site in TiO2 would play the role of primary electron acceptor and T1 site in coordination with TiO2 of integrated Laccase could perform the duty of intra-molecular electron mediator (apparent heterogeneous electron shuttle rate: 2.6 × 10−3 s−1). Electro-catalytic performance on oxygen reduction for Laccase based electrode was limited by the step of substrate diffusion (in the form of free state and entrapment into nano-complex: 2.9 × 10−4 and 1.8 × 10−6 s−1, respectively). As-prepared Lac case based electrode displayed favorable sensing performance to its substrate-dissolved oxygen: high affinity (KM: 46.4 μmol•L−1), moderate detection limit (0.34 μmol•L−1) and enhanced sensitivity (0.021 μA•L•μmol−1).