Electrochemical impedance studies of chitosan-modified electrodes for application in electrochemical sensors and biosensors

Graphite-epoxy resin composite (GrEC) electrodes were modified with chitosan (Chit) films and characterised using electrochemical impedance spectroscopy (EIS). Several film modifications were made using different crosslinking agents: glutaraldehyde (GA), glyoxal (GO), epichlorohydrin (ECH) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) together with N-hydroxysuccinimide (NHS) and the characteristics of each of them evaluated in the presence of model electroactive compounds potassium hexacyanoferrate(III) and hexaammineruthenium(III) chloride. Immobilisation of functionalised carbon nanotubes into chitosan matrices (Chit–CNT) using the same crosslinking agents was also investigated. The impedance of the electrode with the best performance (GrEC/Chit–CNT/EDC–NHS) was characterised as a sensor for dipyrone and hydroquinone and for a glucose biosensor by immobilisation of glucose oxidase (GOx) on top of Chit–CNT using GA. Modelling and equivalent circuit analysis was carried out, with emphasis on diffusion characteristics and the significant features of the spectra are discussed.