ABSTRACTThe oxidation of L-cysteine was studied on a carbon ionic liquid electrode modified with terpyridine copper(II) complex (4′-phenyl-2,2′:6’,2″-terpyridine copper(II)). Cysteine provided an oxidation peak at the relatively low overpotential value of approximately 40 mV at the modified electrode. The oxidation current significantly increased, suggesting high electrocatalytic activity of the terpyridine copper(II) complex toward cysteine. The oxidation current was proportional to cysteine concentration from 0.1 to 40 µM with a limit of detection 0.01 µM. The response of the modified electrode to cysteine was studied in the presence of ascorbic acid, tyrosine, glucose, glycine, uric acid, and dopamine. No interferences were observed. The method was employed for the determination of cysteine in serum.