Development of polymeric sensors for simultaneous determination of melatonin and serotonin for use in biomedical applications

Melatonin and Serotonin involve in many biological and physiological processes in our body. Due to their antioxidant effect, they protect the body against oxidative stress and regulate body homoeostasis; therefore they are increasingly examined with a growing interest. The aim of our work in this context is to improve potentiometric sensors, where screen-printed electrodes with improved selectivity by the polymer are used, in order to determine melatonin and serotonin, which have a biologically important role in our body, as very sensitively and simultaneously. As basic measurement units in our project, ivium stat potentiometer devices were used, the measurements were performed within the 3-electrodes system. Screen-printed electrodes were used as the working electrodes. First, the reduction and oxidation potentials of melatonin and serotonin were electrochemically determined. After that, the electrodes' surfaces were coated with polymer, in order to enhance the selectivity and to prevent biological matrix based attempts. In this context, polymers with polyimide and polyurethane types were used. Melatonin and serotonin was simultaneous monitored at Differential Pulse Voltammetry (DPV) technique with these biosensors prepared on screen-printed karbon electrode surface. In line with the studies on optimization of sensors for melatonin and serotonin determination optimum temperature were determined as 25 °C. Additionally, the best sensor responses were obtained with 0,1 M, pH 7,0 phosphate buffer. The largest linear range for melatonin and serotonin was attained with the biosensor prepared with PU-Caffeic acid-%1 and Poli[2,7-diaminofluorene- pyromellitimide] polymer at 0,2 mM – 1,8 mM concentration interval. pH and temperature optimizations of the prepared sensor were performed. In addition to that, interference effects, thermal stability, operational stability, repeatability and storage stability of the sensor were characterized.