A colorimetric and ratiometric fluorescence dual-mode biosensor based on Pt-Ni bimetallic nanozymes for the detection of ofloxacin drug residues.

Ofloxacin (OFL) is a broad-spectrum and highly effective fluoroquinolone antibacterial agent. The OFL residues threaten food safety, raising public health concerns like allergic reactions and antibiotic resistance. Developing a rapid, highly sensitive detection method is crucial to mitigate these risks. This research engineered a dual-mode (fluorometric/colorimetric) immunosensing system for monitoring OFL residues. Platinum‑nickel nanoparticles (Pt-Ni NPs) characterized by a platinum-rich shell and a nickel-rich core demonstrated high oxidase-like catalytic efficiency. Pt-Ni NPs can quench the fluorescence of red carbon dots (RCDs) and facilitate the catalytic oxidation of o-phenylenediamine (OPD) to its oxidized form (oxOPD). The remaining OPD reacted with potassium permanganate (KMnO₄) to produce ratiometric colorimetry. With escalating OFL concentrations, the red fluorescence of RCDs intensified, and the yellow fluorescence of oxOPD decreased, forming a ratiometric fluorescence response. In the optimized assay regime, the detection range for OFL was 1.0 × 10-7-1.0 × 10-2 mg/mL, with a detection limit of 1.48 × 10-9 mg/mL (ratiometric fluorescence) and 1.36 × 10-8 mg/mL (ratiometric colorimetric). This method demonstrates reliable performance for the detection of OFL residuals in authentic food matrices. The dual-mode sensing strategy offers enhanced sensitivity, rapid response, and straightforward operational, making it a robust analytical tool for food safety monitoring.