Conductive nano nickel oxide/hydroxide paper electrochemical sensor for serotonin detection in genetically engineered <i>Drosophila</i>

Serotonin is considered an integral part in neuropsychiatric diseases, such as major depressive disorder, schizophrenia, post-traumatic stress disorder, obsessive-compulsive disorder, anxiety disorder, and substance use disorder. Understanding the levels of serotonin under different disease conditions is important. Herein, we explored the development of an efficient electrochemical sensor utilizing sustainable paper electrode integrated with nanocomposites through a simultaneous electrochemical deposition strategy. The as-developed sensor is further investigated with surface and electrochemical studies to understand the robust fabrication of the sensor as well as the electrochemical characteristics to show the improved electron transfer kinetics and detection capabilities even in the presence of common interfering biomolecules. The sensor demonstrated a broad linear range from 0.007 nM to 500 μM, with an impressive limit of detection of 0.024 nM for the low concentration range (0.007-0.48 nM) and 383.7 nM for the high concentration range both falling well within the clinically relevant detection levels of serotonin. To evaluate the practical performance, the developed sensor was tested on brain homogenates obtained from genetically modified <i>Drosophila melanogaster</i> models with different serotonin levels. The sensor effectively detected the <i>in vivo</i> changes in serotonin level, and the results were validated against gold-standard HPLC analysis and immunohistochemical staining experiments. The sensors' notable stability, selectivity, and sensitivity towards serotonin make them a valuable tool for neurochemical research and clinical applications, particularly in studying serotonin-related neurological conditions and advancing personalized treatments.