Copper-Based\nElectrochemical Sensor Derived from Thiosemicarbazide\nfor Selective Detection of Neurotransmitter Dopamine

This paper presents the synthesis of the ligand 1-picolinoyl-4-cyclohexyl-3-thiosemicarbazide\n(H<sub>2</sub>pctc) and new metal complexes [Ni(Hpctc)<sub>2</sub>] (<b>1</b>), [Cu(Hpctc)Cl] (<b>2</b>), and [Cd(Hpctc)<sub>2</sub>] (<b>3</b>). The synthesized metal complexes were precisely\ncharacterized using single crystal X-ray diffraction (SC-XRD). In\naddition, complexes <b>1</b>–<b>3</b> were also\ncharacterized by UV–vis, fluorescence, and infrared spectroscopy.\nSC-XRD data confirmed the distorted octahedral geometry around the\nNi(II) and Cd(II) centers and the distorted square planar geometry\naround the Cu(II) center. Data derived from the emission spectra depict\nthat higher fluorescence intensity was exhibited by complexes <b>1</b>, <b>2</b>, and <b>3</b> in comparison to that\nof the free ligand H<sub>2</sub>pctc, and complex <b>3</b> showed\nthe maximum intensity. Further, these metal complex-modified GCEs\n(glassy carbon electrodes) were utilized for electrochemical sensing\nof dopamine (DPM). The electrochemical studies of these complexes\nwere performed using modified glassy carbon electrodes supported by\nelectrical impedance spectroscopy (EIS) and cyclic voltammetry (CV)\nmethods. In contrast to complexes <b>1</b> and <b>3</b>, complex <b>2</b> is a superior electrode material with a\nhigh effective surface area for the electrochemical oxidation of DPM,\naccording to the electrochemical response results. The derived sensor\nhad a wide linear detection range of 1 to 1400 μM, an acceptable\nsensitivity of 0.01531 μA cm<sup>–2</sup> μM<sup>–1</sup>, and a low LOD of 0.38 μM. The proposed approach\nwas free of the interfering effects of ascorbic acid, uric acid, aminophenol,\nand other substances. During the successive scans, no fouling of the\nelectrode surface was observed. The proposed electrochemical sensor\nhad excellent stability, sensitivity, and a low detection limit making\nit suitable for the analysis of a variety of real samples. Additionally,\nit was proven to be useful for analyzing biological fluids.