Development of a di̇sposable sensor for the electrochemical determi̇nation of serotonin

In order to develop an electrochemical 5-HT sensor within the scope of the thesis, first of all, 5 different modifications were made on screen-printed carbon electrodes (SPCE) with different materials. It was determined that the most suitable formulations and materials for the electrochemical determination of 5-HT are zinc oxide nanorod (ZnONR), polymethylene blue (PMB) and gold nanoparticles (AuNP). For the preparation of the 5-HT sensor, firstly, zinc oxide nanorods were modified on the surface of SPCEs by amperometric method. Then, electropolymerization of MB on SPCE/ZnONR electrodes was carried out in ethylene glycol: choline chloride (1:1), a deep eutectic solvent (DES) suitable for green chemistry. Finally, AuNP was coated on SPCE/ZnONR/PMB(DES) electrodes by electrodeposition method. For the optimization of the experimental conditions in the electrochemical determination of 5-HT, the number of cycles of PMB, the pH of the buffer solution, the deposition time in the differential pulse voltammetry technique were studied and it was found to be 30 cycles, pH 7.4 and 150 sec, respectively. Analytical characterizations of the electrochemical 5-HT sensor were performed under optimum conditions. Sensitivity, linear range, limit of detection and limit of quantification of the 5-HT sensor were found to be 0.8976 µA/µM, 0.1 µM – 25 µM, 1.91 nM and 6.38 nM, respectively. The relative standard deviation (RSD) was calculated to be 4.84% (n=5). The behavior of the developed 5-HT sensor in the presence of ascorbic acid and dopamine, 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. In the application and storage stability studies, it was determined that the application stability of the prepared 5-HT sensor was 60 days, and the storage stability was 24 weeks. As a real sample application of the developed 5-HT sensor, 5-HT determination was carried out in human blood serum samples and bananas, and high recoveries were obtained. As a result, a simple, practical, fast, high selectivity, sensitivity, and repeatability, 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.