Electrochemical Behaviour of Microwave-Assisted Oxidized MWCNTs Based Disposable Electrodes: Proposal of a NADH Electrochemical Sensor

The effect of the oxidation degree of multiwalled carbon nanotubes (MWCNTs) for the detection of NADH was evaluated in this paper. MWCNTs were oxidized by microwave-assisted sulfonitic treatment at different times (5, 10, 15, and 30min) and deposited onto a graphite screen printed electrodes. Oxidized MWCNTs were characterized and the electrochemical performance evaluated. The best sensor in terms of sensitivity and stability was obtained after 15minutes of oxidation (SPE/CNT15). A significant reduction of the NADH oxidation potential was recorded for oxidized MWCNTs compared with unmodified MWCNTs (0.270V and 0.500V, respectively vs. Ag/AgCl pseudo reference electrode), increasing the selectivity of the system. Chronoamperometric calibration curves carried out applying a potential of 0.3V for 1min were linear in the 4-35μM range of NADH. A limit of detection of 1μM was achieved with negligible surface fouling (three consecutive calibration curves, 30 total measurements: slope decrease 5.9%). Inter electrode reproducibility (n=13) was good resulting in RSD of 15.2% and 5.0% for the peak intensity and the oxidation potential, respectively. Quantification of glucose in white wine samples was carried out to demonstrate the ability of the NADH sensor to work in real samples. A good correlation with a spectrophotometric kit for the glucose quantification was achieved.