Electrochemical detection of melatonin using Gd-doped ZnO nanoparticles modified carbon paste electrode

In this work, we report the synthesis of gadolinium-doped ZnO nanoparticles (GZ Nps) with varying dopant concentrations (2, 5 and 10 % GZ Nps) to detect melatonin (MEL) through the fabrication of the modified carbon paste electrode (MCPE). Additionally, these Nps are examined for biomedical research and as a photocatalyst for the degradation of Rhodamine B dye. The study is focused on synthesizing GZ Nps using a sustainable green approach incorporating phytochemicals sourced from Tabernaemontana divaricata (T. divaricata) in the simple, economical and environmentally friendly co-precipitation method. Further, the analysis of as-synthesized GZ Nps by X-ray powder diffraction, field emission scanning electron microscopy and transmission electron microscopy analysis confirmed spherical morphology and better crystallinity with lesser agglomeration when the dopant ion concen­tration was increased. GZ Nps served as an effective photocatalyst for the degradation of Rhodamine B dye, achieving maximum degradation efficiency of 96.70 % for 2 % GZ sample. Furthermore, the antibacterial activity was tested using inhibitory zone radius measure­ments. In electrochemical studies using cyclic voltammetry and differential pulse voltam­metry techniques, it was found that 5%GZ Nps, utilized to fabricate a GZ Nps modified carbon paste electrode (GZ/MCPE), showed excellent sensitivity for MEL alone and for the simultaneous detection of ciprofloxacin and MEL. By changing MEL concentrations, the limit of detection of MEL was determined to be 7.95 µM.