Electrochemical study of some selected neurotransmitters at metal oxide doped phthalocyanine supported on carbon nanotubes sensor platform

Abstract

The electrocatalytic properties of metal oxides (MO = Fe₃O₄, ZnO) nanoparticles doped phthalocyanine (Pc) and functionalized multi-walled carbon nanotubes (MWCNTs), decorated on glassy carbon electrode (GCE) was investigated. Successful synthesis of the metal oxide nanoparticles and the MO/Pc/MWCNT composite were confirmed using Ultraviolet-visible spectrophotometry (UV-Vis), Energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and Transmission electron microscopy (TEM) techniques. Successful modification of GCE with the MO and their composite was also confirmed using cyclic voltammetry (CV) technique. The potential of the developed sensor towards dopamine (DA) oxidation was explored using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopic (EIS). Results indicate that GCE-MWCNT/Fe₃O₄/2,3-Nc, GCE-MWCNT/Fe₃O₄/29H,31H-Pc, GCE-MWCNT/ZnO/2,3-Nc and GCE-MWCNT/ZnO/29H,31H-Pc modified electrodes demonstrated fast electron transport or lower charge transfer resistance, and enhanced DA oxidation current compared with other electrodes studied. Electroanalysis results indicated that the four GCE-MWCNT/MO/Pc modified electrodes were stable towards DA oxidation with minimum current drop (5-10%) after 20 scans. GCE-MWCNT/ZnO/29H,31H-Pc was the best electrode towards DA detection with very low detection limit (0.75 μM) that compared with literature, good sensitivity (1.45 μA/ μM), resistance to electrode fouling, and excellent ability to detect DA without interference from ascorbic acid (AA) signal. Electrocatalytic oxidation of DA on GCE-MWCNT/ZnO/29H,31H-Pc electrode was diffusion controlled but characterized with some adsorption of electro-oxidation reaction intermediates products. The fabricated sensors are easy to prepare, cost effective and can be applied for real sample analysis of dopamine in biological samples. Furthermore, glassy carbon electrode (GCE) was also modified with metal oxides (MO = Fe₃O₄, ZnO) nanoparticles doped phthalocyanine (Pc) and functionalized MWCNTs, and the electrocatalytic properties was studied. Successful synthesis of the metal oxide nanoparticles and the MO/Pc/MWCNT composite were confirmed using Fourier transform infrared spectroscopy (FTIR), Raman and Scanning electron microscopy (SEM) techniques. The electrodes were characterised using cyclic voltammetry (CV) technique. The electrocatalytic behaviour of the electrodes towards epinephrine (EP) and norepinephrine (NE) oxidation was investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopic (EIS). Result showed that GCE-MWCNT/Fe₃O₄/2,3-Nc, GCE-MWCNT/Fe₃O₄/29H,31H-Pc, GCE-MWCNT/ZnO/2,3-Nc and GCE-MWCNT/ZnO/29H,31H-Pc electrodes gave enhanced EP and NE current response. Stability study indicated that the four GCE-MWCNT/MO/Pc modified electrodes were stable against electrode fouling effect with the percentage NE current drop of 5.56%, 5.88%, 5.56% and 5.56% for MWCNT/Fe3O4/2,3-Nc, MWCNT/Fe₃O₄/29H,31H-Pc, MWCNT/ZnO/2,3-Nc and MWCNT/ZnO/29H,31H-Pc modified electrodes respectively after 20 scans. GCE-MWCNT/ Fe₃O₄/29H,31H-Pc gave the lowest limit of detection (4.6 μM) towards EP while MWCNT/ZnO/29H,31H-Pc gave the lowest limit of detection (1.7 μM) towards NE. The limit of detection and sensitivity of the electrodes compared well with literature. Electrocatalytic oxidation of EP and NE on GCE-MWCNT/MO/Pc electrodes was diffusion controlled with some adsorption of electro-oxidation reaction intermediates products. The electrodes were found to be electrochemically stable, reusable and can be used for the analysis of EP and NE in real life samples.