Simultaneous Voltammetric Determination of Neurodegenerative Biomarkers at Nanomolar Levels Using a Fe3O4 Nanoparticle-Decorated Glassy Carbon Microsphere Nanocomposite

Abstract The precise monitoring of dopamine (DA), serotonin (5-HT), and L-tryptophan (L-Trp) is a critical challenge for the early diagnosis and management of neurodegenerative disorders, such as Alzheimer’s and Parkinson’s diseases. This work describes the development of a high-performance electrochemical platform based on a carbon paste electrode modified with a novel nanocomposite of glassy carbon microspheres (GCMs) decorated with magnetite (Fe 3 O 4 ) nanoparticles. The modifier was synthesized through a sustainable and efficient hydrothermal route, which ensured a uniform decoration of the GC surface and enhanced the material’s synergistic electrocatalytic properties. Under optimized conditions using square wave voltammetry (SWV) at pH 7.50, the sensor achieved wide linear response ranges: 0.04–10.00 µM for DA and 0.09–20.00 µM for 5-HT and L-Trp. Remarkably low limits of detection (LOD) were obtained for simultaneous determination: 2.8 nM for DA, 8.1 nM for 5-HT, and 6.7 nM for L-Trp. The proposed analytical method was successfully validated in complex biological matrices, including blood serum and synthetic urine, providing excellent recovery rates (near 100%) and high precision (RSD < 5%). Furthermore, the sensor demonstrated exceptional selectivity against common physiological interferents, long-term stability, and high reproducibility. These results demonstrate that the Fe 3 O 4 /GCM platform is a sensitive and promising tool with significant potential for future clinical diagnostics.