Simultaneous electrochemical detection of serotonin and ascorbic acid at MWCNT- antimony oxide nanocomposite modified electrode

MSc (Chemistry), North-West University, Mahikeng Campus

Abnormal neurotransmitters (NTs) levels have been reported to cause various neurological diseases and disorders such as bipolar disorder, borderline personality disorder, social phobia, schizotypal personality disorder, attention deficit hyperactivity disorder (ADHD), Alzheimer's disease and Parkinson’s disease, etc. Therefore, a simple, affordable, user-friendly, quick, and highly sensitive detection method is required. Electrochemical techniques offer such advantages, henceforth; this work describes the fabrication of an electrochemical sensor made-up of multi-walled carbon nanotube- antimony oxide (MWCNT-AONP) nanocomposite embedded on screen-printed carbon electrodes (SPCEs) to simultaneously detect ascorbic acid (AA) and serotonin (5-HT). Various spectroscopic and microscopic techniques were used to confirm the successful synthesis of the nanomaterials, including fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, x-ray diffractogram (XRD) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive x-ray (EDX) spectroscopy. Cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques were used to investigate the electrochemical properties of the electrodes. Compared to other electrodes tested, the MWCNT-AONP electrode demonstrated better electron transport and improved electrocatalytic response towards 5-HT and AA detection. For 5-HT detection, the SPCE@AONP-MWCNT electrode displayed the sensitivity, and limit of detection (LOD) of 0.2863 μA/μM, and 24 nM, with a linear range of 1.56 x 10-8 – 1.28 x 10-7 M respectively, and 0.4789 μA/μM, and 278 nM in the 1.60 x 10-8 – 6.40 x 10-7 M concentration range for AA detection using SWV. Three well-separated oxidation peaks were observed in a mixed system containing AA, 5-HT, and dopamine (DA); the 5-HT– DA and DA–AA potential separations were 170 and 250 mV, respectively, owing to the synergistic effect of multi-walled carbon nanotubes (MWCNTs), and antimony oxide nanoparticles (AONPs). Linear responses were obtained for 5-HT, and AA in the 35 – 205 μM (R2 = 0.9940), and 45 – 190 μM (R2 = 0.9927) concentration ranges, with detection limits of 24 and 17 μM, respectively. Compared to the literature, the acquired LOD values for detecting AA and 5-HT were better. The proposed electrode exhibited excellent selectivity and outstanding anti-interference behaviour. The applicability of the sensor to detect AA and 5-HT in oranges and tomatoes exhibited outstanding recoveries above 99.12 and 91.32 %, with RSD (relative standard deviation) values of 3.52 and 2.57 %, respectively. The obtained results underpin the fabricated sensor’s potential applicability to determine AA and 5-HT simultaneously in bodily fluids.

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