Microscopy techniques for the characterization of modified electrodes in the development of glucose biosensors

Microscopy techniques were used to study films of a hydrotalcite-like compound electrosynthesised on a Pt electrode, entrapping glucose oxidase. SECM study has been carried out to probe local enzymatic activity and to obtain topographic images of the modified electrode, which can be used as glucose amperometric biosensor. Due to the complexity of the investigated system, different configurations were considered, starting from the Pt surface only modified with the inorganic clay, up to the optimized biofilm, with glucose oxidase stabilized by cross-linking with glutaraldehyde. SECM was used to detect the activity of the entrapped enzyme by observing the feedback current in a solution of K4[Fe(CN)6] and glucose in phosphate buffer, when K3[Fe(CN)6] was generated at the tip.It was demonstrated that the enzyme distribution was not homogeneous all over the electrode surface, but it reflected the distribution of the underlying electrosynthesised inorganic film. SECM gave only poor topographic information about the complex samples studied, but the images were in good agreement with those provided by other microscopy techniques.