Development and Application of Chemically Modified Electrodes for Sensing and Electrocatalysis

An electrochemical sensor based on a glassy carbon electrode (GCE) modified by a thin film of hybrid copper cobalt hexacyanoferrate (Cu-CoHCF) was prepared and tested for the determination of three thiols: L-cysteine (CySH), L-glutathione (GSH) and 1,4-butanedithiol (BdSH). Cyclic voltammetry (CV) measurements were carried out with the as prepared and thermally treated chemically modified electrode (CME) in phosphate buffer solution from pH 2 to 7. CV results showed that at pH higher than 5, the Cu-CoHCF layer was unstable and underwent significant fouling. Then, chronoamperometric measurements were carried out to develop an analytical method for the determination of thiols. Cysteine showed the lowest limit of detection (7.5 × 10-7 M), but GSH and BdSH also showed good results. The above sensor was also employed for the indirect determination of Hg2+. It exploits the formation of a redox inactive complex with thiols. CySH and BdSH were used, with the former giving more sensitive results. Interference studies led to Cu2+ being the major interferent. The interference from Cu2+ was avoided by exploiting the faster reaction kinetics between CysH and Hg2+. GCE were also modified by carbon nanomaterials, graphene oxide, GO, and multi-walled carbon nanotubes alone, mixed together (Composite) or in the form of bi-layers. The reduction of GO was carried out by means of a green approach using electroreduction. Catechol and dopamine, which are representative of polyphenols class were investigated to find which of them allows the best electron transfer kinetics. To this aim the fouling effects of the electrode surface were also taken into account. The electrochemically active areas were estimated by using two approaches in order to highlight the different phenomena that could affect the redox processes of the two analytes at the different CME. The Composite configuration displayed the best compromise in terms of sensitivity and resistance to fouling.