Scanning electrochemical microscopy activity mapping of electrodes modified with laccase encapsulated in sol–gel processed matrix

Electrodes modified with sol–gel encapsulated laccase (isolated from Cerrenaunicolor) exhibiting mediated or mediatorless bioelectrocatalytic dioxygen reduction activity were inspected using confocal laser scanning microscopy, atomic force microscopy and scanning electrochemical microscopy. Potential-driven leaching of the redox mediator 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) from carbon ceramic electrodes covered by hydrophilic silicate-encapsulated laccase was detected during electrocatalytic action. Strongly non-homogeneous lateral distribution of the activity towards dioxygen reduction was found by redox competition mode of scanning electrochemical microscopy using a similar electrode with syringaldazine as redox mediator. Hydrogen peroxide formation at these electrodes is detected at potentials lower than 0.05 V. It is ascribed to the electrochemical oxygen reduction at the carbon material while laccase-catalyzed oxygen reduction occurs below 0.35 V without hydrogen peroxide formation. The scanning electrochemical microscopy images of electrodes consisting of single-walled carbon nanotubes non-covalently modified with pyrenesulfonate and laccase encapsulated in a sol–gel processed silicate film confirm direct electron transfer electrocatalysis in redox competition mode experiments and show that the enzyme is evenly distributed in the composite film. In conclusion scanning electrochemical microscopy proved to be useful for mapping of enzyme activity on different materials.