Electrochemical melatonin detection in extrapineal tissue using a bioconjugated sensor

Melatonin (N-acetyl-5-methoxytryptamine) is a neurohormone predominantly synthesized in the pineal gland and widely known for its role in circadian rhythm regulation. Beyond its chronobiological function, melatonin exhibits potent antioxidant and cytoprotective activities, and reduced endogenous levels have been associated with the progression of several neurodegenerative disorders. These factors highlight the need for rapid and accurate analytical strategies for the detection of melatonin in complex biological matrices. In this study, we developed an immunosensor for proof-of-concept sensing in complex biological matrices (kidney, heart, and liver) of Wistar rats. Tissues from treated and control groups were spiked with a commercial melatonin standard and analyzed using the proposed platform. The gold electrode was functionalized with an anti-melatonin antibody to form a sensing interface. The sensor was characterized by Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), and Square Wave Voltammetry (SWV). The platform exhibited a limit of detection (LOD) of 4 µM, a limit of quantification (LOQ) of 14 µM, and a sensitivity of 250 µA µM −1 cm −2 . The detectable melatonin levels in the evaluated tissues are likely influenced by the matrix complexity. These findings demonstrate the potential of the Au/SAM-MUA/anti-ME immunosensor as a proof-of-concept tool for the monitoring of melatonin-associated responses in tissue homogenates.