Simultaneous deposition of Prussian Blue and creation of an electrostatic surface for rapid biosensor construction

Polyethyleneimine (PEI) was deposited onto the surface of the screen-printed carbon electrode (SPCE) through simple adsorption from aqueous solution. Anion-exchange properties of the deposited PEI were then employed to confine ferricyanide ions [Fe(CN)6]3− within the polymeric layer. After that, the resulting electrode was washed and incubated in FeSO4 solution so that Fe2+ cations could react with the adsorbed [Fe(CN)6]3−. The reaction led to the formation of surface-confined Prussian Blue (PB) crystals that were highly active in the electrochemical reduction of hydrogen peroxide. During the formation of PB, negatively charged ferricyanide ions complexed with charged iron(II) ions thereby regenerating positive charges on the PEI and enabling electrostatic adsorption of enzymes. After glucose oxidase (GOx) was immobilised in this manner on the surface of a PEI/PB modified electrode an amperometric biosensor for glucose was produced which could sense the analyte at voltages as low as 0 mV, thus eliminating the redox activity of many common interferents. Within this report, we use GOx as a model enzyme to demonstrate principle. However, the methodology reported is amenable to immobilising virtually any enzyme whilst simultaneously depositing PB mediator.