Dextran-integrated polypyrrole-Cu2O composite for improved electrochemical quantification of melatonin in biological samples

Monitoring the level of melatonin (MEL), a neurohormone that plays a vital role in governing the body's circadian rhythms and sleep cycles, is critical due to its physiological importance and potential adverse side effects during overexposure. This research deals with the design and development of a novel electrochemical sensor by modifying a glassy carbon electrode (GCE) with a composite of poly(vinyl alcohol) (PVA), dextran (Dex), polypyrrole (PPy) and copper oxide particles (Cu₂O) forming the PDPC composite. The synthesized composite was analyzed using both structural and morphological characterization methods. Additionally, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were conducted to examine electrochemical behaviour of the composite. Significantly, the dextran inclusion, which is a biocompatible polysaccharide, makes the composite more hydrophilic, film forming, and stable enhancing sensor properties, more importantly, electrochemically. The sensor showed high electrocatalytic activity towards MEL oxidation as studied using CV and DPV. For MEL oxidation, the oxidation peak was found at +0.6 V in phosphate buffer (pH 7.0) with an increase in current with respect to melatonin concentration. The sensor has a detection limit of 5.2 nM with a linear range of 10.0 nM to 850.0 μM, found to be better than most reported sensors. Analysis of real samples, such as human serum and urine, demonstrated the ability to selectively, stably, and reproducibly detect MEL. These data confirm the potential possibilities of using the sensor for clinical and point-of-care testing showing a significant development in polysaccharide-based electrochemical sensors.