Phenoxazine functionalized, exfoliated graphite based electrodes for NADH oxidation and ethanol biosensing

Exfoliated graphite (EG) particles covalently functionalized with phenoxazine-based molecules have been used to prepare bulk-modified electrodes. The electrodes are of two types: 1) binder-less covalently modified EG pellets and 2) sol-gel derived composites of silicate and modified EG particles. The covalent modification is confirmed by infrared spectroscopy. The electrochemistry of attached molecules has been carried out to decipher the catalytic activity of immobilized phenoxazines towards NADH oxidation. Fast response time of about 4-6 seconds and a low detection limit of 20 muM have been achieved using these electrodes. The sensor is found to yield a linear range of current response versus concentration between 0.02 and 1 mM of NADH. Biosensing in presence of alcohol dehydrogenase enzyme and NAD(+) shows a linear response between 1 and 13 mM and the response time for alcohol sensing is found to be 20-30 s. These electrodes are found to be very stable during operation and can be stored without any deterioration over a period of several months.