Sensitive and selective electrochemical sensor for serotonin detection based on ferrocene-gold nanoparticles decorated multiwall carbon nanotubes

Serotonin, or 5-hydroxytryptamine (5-HT), is a neurotransmitter that plays a crucial role in neural activities. 5-HT deficiency is clinically related to several psychiatric disorders. Therefore, sensitive 5-HT detection is critical in the diagnosis of diseases associated with neurological disorders. Here we developed a sensitive electrochemical sensor utilizing ferrocene covalently linked gold nanoparticles on multiwall carbon nanotubes (FeC-AuNPs-MWCNT), electrocatalytic nanocomposites, to enhance 5-HT detection. FeC-AuNPs-MWCNT modified screen-printed carbon electrodes (SPCEs) provide catalytic activity towards 5-HT oxidation from both FeC and AuNPs along with the high conductance from the carbon nanotube network. The FeC-AuNPs-MWCNT was synthesized by chemically reducing AuNPs on MWCNT surfaces and covalently attaching FeC to the AuNPs. Square wave voltammetry analyses confirmed that the electrocatalytic nanocomposite modified electrodes improved the electrocatalytic activity towards 5-HT oxidation, 61 times higher than the unmodified SPCE. The sensor exhibited a sensitive response to 5-HT over a wide dynamic range from 0.05 µM to 20 µM, a limit of detection of 17 nM (S/N = 3), excellent reproducibility, and high selectivity towards 5-HT against several interferers, including ascorbic acid, urea, uric acid, dopamine, and glucose. The sensor was successfully demonstrated to detect sub-µM 5-HT in urine samples with satisfactory recoveries (98.3–104.9%) and a low relative standard deviation of less than 3%. This sensitive, selective, and cost-effective electrochemical sensor shows great promise in direct 5-HT analysis for clinical applications.