Glucose oxidase enzyme inhibition sensors for heavy metals at carbon film electrodes modified with cobalt or copper hexacyanoferrate

Electrochemical enzyme sensors prepared from cobalt or copper hexacyanoferrate modified carbon film electrodes plus glucose oxidase (GOx) immobilised by crosslinking with glutaraldehyde were successfully applied to the determination of heavy metal cations using fixed potential amperometry. Sensor performance was optimised with respect to the applied potential and influence of pH of the electrolyte solution. Cadmium, cobalt, copper and nickel ions were detected in the presence of fixed amounts of glucose, and the response to glucose was tested in the absence and presence of a fixed concentration of inhibitor. Electrochemical impedance spectroscopy was used for the first time to characterise the response of glucose biosensors in the presence of the inhibitors. The enzyme inhibition mechanism is reversible and competitive and 10% enzyme inhibition was achieved with submicromolar or micromolar concentrations of the metal cations.