Competitive surface-blocking electrochemical sensor for fosfomycin detection based on ferrocen-tagged surface chemistry.

A disposable electrochemical sensor based on a competitive surface-blocking mechanism driven by covalent epoxide–amine coupling is reported for the selective voltammetric determination of fosfomycin (Fos). The sensing strategy employs ferrocen (Fc)-tagged surface chemistry as a redox reporter, where Fc surface occupancy inversely reflects Fos binding to cysteamine-derived amine groups. Screen-printed carbon electrodes (SPCEs) modified with a reduced graphene oxide/gold nanoparticle (rGO/AuNP) nanocomposite provide enhanced electroactive surface area and improved electron-transfer kinetics. Increasing Fos concentrations progressively consume surface amines, reducing Fc labeling and leading to a concentration-dependent decrease of the differential pulse voltammetric oxidation signal. Under optimized conditions, the sensor exhibits a linear response from 50 to 2000 µM with a limit of detection of 10 µM, matching the clinically relevant mid-therapeutic range of intravenous fosfomycin therapy (≈ 7–276 mg L⁻¹). Matrix effects are effectively minimized by controlled serum dilution, enabling accurate Fos quantification with recoveries of 97.8–103.7% and without extensive sample pretreatment. The platform retains stable performance for at least 15 days at 4 °C. Rather than replacing chromatographic techniques, this proof-of-concept platform is positioned as a rapid, low-cost, and portable electrochemical tool for routine therapeutic drug monitoring and point-of-care screening.