Ghaffari, NastaranBaker, Priscilla2026-09-042026-09-042026Ghaffari, N. and Baker, P., 2026. Thiol-mediated electrochemical sensor for the breast cancer biomarker CA 15-3. Frontiers in Sensors, 7, p.1807434.https://doi.org/10.3389/fsens.2026.1807434https://hdl.handle.net/10566/25346Cancer antigen 15-3 (CA 15-3), a circulating fragment of the MUC1 glycoprotein, is widely used for monitoring breast cancer progression. In this study, we report a label-free, receptor-free electrochemical detection strategy based on adsorption-mediated modulation of gold surface oxidation. Pencil graphite electrodes (PGEs) were modified with electrochemically deposited gold nanoparticles (AuNPs) using a reproducible multi-electrode fabrication system. The nanostructured AuNP surface exhibited enhanced electroactive area and improved electron-transfer properties, as confirmed by ferri/ferrocyanide characterization. Analytical detection was performed in phosphate-buffered saline by monitoring the intrinsic gold oxidation peak. Following incubation with CA 15-3, a concentration-dependent decrease in the gold oxidation current was observed, attributed to adsorption-induced surface passivation of electrochemically active gold sites. The platform demonstrated a linear response across the tested concentration range with a calculated limit of detection of 1.2 × 10−4 U/mL. Measurements in spiked plasma samples confirmed the feasibility of detecting CA 15-3 in complex matrices under controlled conditions. This work establishes a chemically driven, adsorption-based electrochemical sensing strategy that exploits gold surface chemistry for label-free biomarker detection.enbreast cancer biomarker CA 15-3electrochemical depositiongold nanoparticlesmultiple coating techniquepencil graphite electrodeArticle