Zinc oxide nanorod/polymethylene blue (deep eutectic solvent)/gold nanoparticles modified electrode for electrochemical determination of serotonin (5-HT)

Low or high levels of serotonin (5-HT) in the blood serum are linked to various diseases such as Alzheimer's, depression, anxiety, and carcinoid syndrome. In this study, a disposable sensor was developed for the low-cost, rapid, and practical determination of 5-HT. Firstly, zinc oxide nanorods (ZnONR) were modified on the surface of SPCEs by amperometric method. Then, electropolymerization of methylene blue (MB) on SPCE/ZnONR elec-trodes was carried out in ethylene glycol/choline chloride, a deep eutectic solvent (DES) suitable for green chemistry. Finally, AuNP was coated on SPCE/ZnONR/PMB(DES) electrodes by electrodeposition method. The materials of ZnONR, PMB(DES), and AuNP were characterized by FE-SEM-EDX, FTIR, and XRD. Sensitivity, linear range, the limit of detection, and limit of quantification of the 5-HT sensor were found to be 0.8976 mu A mu M-1, 0.1 mu M - 25 mu M, 1.91 nM, and 6.38 nM, respectively. Reproducibility, repeatability, stability (application and storage), reusability, and fouling effect of the 5-HT sensor were examined. The behavior of the developed 5 -HT sensor in the presence of ascorbic acid, dopamine, uric acid, glucose, epinephrine, and norepinephrine, which are electroactive analytes that can interfere, was examined and it was found that the sensor was much more sensitive to 5-HT compared to other analytes. As a real sample application of the developed 5-HT sensor, the 5 -HT determination was carried out in human blood serum samples, and high recoveries were obtained. As a result, a simple, practical, fast, high selectivity, sensitivity, repeatability, reproducibility, and the low-cost, disposable electrochemical sensor was developed for the determination of 5-HT. The developed 5-HT sensor can be used in point-of-care tests.