Bioelectrocatalytic dioxygen reduction at hybrid silicate–polyallylamine film with encapsulated laccase

The tin-doped indium oxide (ITO) electrode served as a suitable support for the mediator 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) and extracellular laccase from Cerrena unicolor encapsulated in sol–gel processed thin hydrophilic silicate/polyallylamine film. For some experiments the electrode was premodified with tin-doped indium oxide nanoparticles (ca. 20 nm in diameter). After initial decrease of the current the electrode shows stable voltammetry of the immobilised mediator. This indicates that silicate/polyallylamine film to prevent water soluble mediator ions expulsion into the aqueous solution. The modified electrode exhibits electrocatalytic response towards dioxygen reduction. Both the magnitude of voltammetric current corresponding to the redox process of mediator and the catalytic current is dependent on the order of deposited components. The magnitude of the catalytic current with immobilised mediator is larger than when mediator is present only in the buffer solution. The efficiency of the electrocatalytic process is also more than twice increased (reaching 0.25 mA cm−2) by electrode premodification with ITO nanoparticles.