Electrochemical sensing based on redox mediation at carbon nanotubes

An electrochemical sensing platform was developed based on the integration of redox mediators and carbon nanotubes (CNT) in a polymeric matrix. To demonstrate the concept, a redox mediator Azure dye (AZU) was covalently attached to polysaccharide chains of chitosan (CHIT) and interspersed with CNT to form composite films for the amperometric determination of beta-nicotinamide adenine dinucleotide (NADH). The incorporation of CNT into CHIT-AZU matrix facilitated the AZU-mediated electrooxidation of NADH. In particular, CNT decreased the overpotential for the mediated process by an extra 0.30 V and amplified the NADH current by approximately 35 times (at -0.10 V) while reducing the response time from approximately 70 s for CHIT-AZU to approximately 5 s for CHIT-AZU/CNT films. These effects were discussed in terms of the AZU/CNT synergy, which improved charge propagation through the CHIT-AZU/CNT matrix. The concept of CNT-facilitated redox mediation in polymeric matrixes has a potential to be of general interest for expediting redox processes in electrochemical devices such as sensors, biosensors, and biological fuel cells and reactors.