Synergistic moxifloxacin detection: AgNPs/GO electrochemical immunosensor with oriented antibody immobilization

Moxifloxacin (MXF), a broad-spectrum fluoroquinolone antibiotic, is widely used in human and veterinary medicine. However, its overuse leads to environmental residues and antimicrobial resistance, posing significant health risks. Herein, a label-free electrochemical immunosensor was developed for ultrasensitive MXF detection using silver nanoparticle-graphene oxide nanocomposites (AgNPs/GO). The synergistic effects of GO (high conductivity) and AgNPs (redox activity) enhanced electron transfer efficiency. Critically, Staphylococcal protein A (SPA) enabled oriented Fc-directed antibody immobilization, significantly enhancing antigen-binding efficiency and sensitivity compared to random adsorption. Material characterization (UV-Vis, XRD, SEM, TEM) confirmed the nanostructure. The sensor exhibited a wide linear range (0.50-200 ng/mL), ultralow detection limit (0.18 ng/mL, S/N = 3), and high specificity against structural analogs. Practical validation in spiked pork and milk samples achieved recoveries of 95-104 % with long-term stability (>82.5 % signal retention over 28 days). This work provides a reliable platform for monitoring antibiotic residues in food safety systems.