Selective nanomolar electrochemical detection of serotonin, dopamine and tryptophan using TiO2/RGO/CPE – influence of reducing agents

Abstract

TiO₂/RGO nanocomposites were synthesised via a simple one-pot hydrothermal method. The influence of different reducing agents on the composite preparation was systematically studied. Electrochemical sensors were developed using the synthesised TiO₂/RGO nanocomposites as modifiers in a carbon paste electrode. The nanocomposite formed using sodium borohydride as the reducing agent exhibited superior electrochemical properties compared to other modified electrodes. The electrochemical sensing properties of the modified electrodes were studied using different electrochemical techniques, namely, cyclic voltammetry, differential pulse voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The electrochemical surface areas of all the modified electrodes were significantly improved, and their charge transfer resistance was substantially reduced by modification. Cyclic voltammetry studies revealed the quasi-reversible nature of dopamine and irreversible nature of serotonin (SER) and tryptophan (TRP) at neutral pH. Differential pulse voltammetric studies using the modified electrodes were utilised for ultra-trace level sensing of neurotransmitters. Detection limits as low as 0.18 nM, 0.32 nM and 0.4 nM for serotonin (SER), dopamine (DP) and tryptophan (TRP) were achieved. The modified electrodes exhibited a wide linear dynamic range, which allowed the simultaneous determination of the biomolecules SER, DP and TRP. Real sample analysis, stability measurements and reproducibility tests further demonstrated the practical applicability of the developed electrochemical sensor.