Nafion- and AuNP-Modified Four-Bore Carbon Fiber Microelectrode for Simultaneous FSCV Detection of Neurotransmitters and Heavy Metals

Neurodegenerative diseases are a growing global concern, with patient numbers steadily increasing. Early diagnostic tools and improved therapeutic strategies are urgently needed. The roles of co-transmission and environmental factors, such as chronic exposure to toxic heavy metals, remain underexplored due to the lack of analytical platforms capable of real-time, multiplex detection of multiple analytes in complex biological matrices. In this study, we developed a laser-trimmed, surface-modified four-bore carbon fiber microelectrode (CFM) for the simultaneous detection of neurotransmitters and toxic heavy metals using fast-scan cyclic voltammetry (FSCV). The sensor incorporates four individual carbon fibers protruding from separate bores in a customized glass capillary, enabling independent operation of each fiber to prevent crosstalk and optimize selectivity. Two detection strategies were employed: (a) electrodeposition of gold nanoparticles (AuNPs) for detecting cadmium in the presence of copper, arsenic, and dopamine, and (b) selective Nafion coating on two diagonally opposed fibers to distinguish dopamine and serotonin from ascorbic acid and 5-hydroxyindoleacetic acid in tris buffer. The four-bore CFM produced distinct, well-resolved peaks for each analyte, with higher sensitivity and lower detection limits than single-bore CFMs. It uniquely enabled quantification of As³⁺ in mixed analyte solutions, which single-bore CFMs failed to detect, and significantly enhanced sensitivity for dopamine and serotonin in interference studies. The sensor maintained stable performance over consecutive injections, confirming its robustness for continuous monitoring. This four-bore FSCV platform offers a promising tool for real-time, concurrent monitoring of neurochemicals and toxic metals, opening new opportunities to study their combined impact on neurodegeneration and for future in vivo applications.