Laser-Trimmed, Surface-Functionalized Four-Bore CFMs Enable Co-Detection of Neurochemicals and Toxic Metal Ions

Simultaneous detection of multiple neurochemicals and toxic metal ions in real time remains a major analytical challenge in neurochemistry and environmental sensing. In this study, we present a novel, biocompatible, laser-trimmed four-bore carbon fiber microelectrode (CFM) platform capable of ultra-fast, multi-analyte detection using fast-scan cyclic voltammetry (FSCV). Each of the four carbon fibers, spaced nanometers apart within a glass housing, was independently functionalized and addressed with a distinct waveform, allowing the selective and concurrent detection of four analytes without electrical crosstalk. To validate the system, we developed two electrochemical detection paradigms: (1) selective electrodeposition of gold nanoparticles (AuNPs) on one fiber for enhanced detection of cadmium (Cd2+), alongside dopamine (DA), arsenic (As3+), and copper (Cu2+); and (2) Nafion-modification of two diagonally opposing fibers for discriminating DA and serotonin (5-HT) from their interferents, ascorbic acid (AA) and 5-hydroxyindoleacetic acid (5-HIAA), respectively. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis confirmed surface modifications and the spatial localization of electrodeposited materials. Electrochemical characterization in tris buffer, which mimics artificial cerebrospinal fluid, demonstrated enhanced analytical performance. Compared to single-bore CFMs, the four-bore design yielded a 28% increase in sensitivity for Cd2+ (147.62 to 190.02 nA µM−1), 12% increase for DA (10.785 to 12.767 nA µM−1), and enabled detection of As3+ with a sensitivity of 0.844 nA µM−1, which was not possible with single-bore electrodes within the mixture of analytes. Limits of detection improved twofold for both DA (0.025 µM) and Cd2+ (0.005 µM), while As3+ was detectable down to 0.1 µM. In neurotransmitter-interference studies, sensitivity increased by 39% for DA and 33% for 5-HT with four-bore CFMs compared to single-bore CFMs, despite modest Nafion diffusion onto adjacent fibers. Overall, our four-bore CFM system enables rapid, selective, and multiplexed detection of chemically diverse analytes in a single scan, providing a highly promising platform for real-time neurochemical monitoring, environmental toxicology, and future integration with AI-based in vivo calibration models.