Electrochemical response and impedimetric behaviour of dopamine and epinephrine at platinum electrode modified with carbon nanotubes-gold nanocomposite

A Platinum (Pt) electrode was modified with gold and gold oxide nanoparticles electrodeposited on multi-walled carbon nanotubes. The modified electrodes were characterised with techniques such as Transmission Emission Microscopy (TEM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDX). The electrochemical properties were investigated using cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy. The electrodes were used as analytical probes towards the detection of dopamine (DA) and epinephrine (EP). Results showed that Pt-MWCNT-Au electrode gave the best dopamine and epinephrine current response at lower charge transfer resistance R_ct values of 9.1 and 9.4 Ωcm² in DA and EP respectively compared with other electrodes. The electrooxidation of the analyte involved adsorbed intermediates with adsorptive capacitance (Cads) and Tafel values of, 331.6 μFcm^-2, 136.4 mVdec^-1 in DA; and 225.2 μFcm^-2, 162.8 mVdec-1 in EP. The limit of detection were 78±6.5 nM and 350±28.4 nM while the catalytic rate constant (K) were (13.8±2.4) and (18.9±4.2) x 10⁸ cm³ mol^-1 s^-1 for DA and EP respectively on the electrode. The limit of detection is favourable for DA detection in biological system where DA exists in μM concentration. The electrode was easy to prepare and was also electrochemically stable such that it could be used for the detection of DA and EP in the presence of interfering species such as ascorbic acid (AA).