Amperometric responses (E=−0.05V) of the glassy carbon electrodes modified with the original (a), water-boiled (b), and acid-microwaved (c) CNT to additions of NADH aliquots. The current steps correspond to 0.010, 0.025, 0.050, 0.10, 0.25, 0.50, 1.0, 2.0, 3.0, 5.0, and 10.0 mM NADH. Inset: The related calibration curves.