Development of plasmonic biosensor with tooth-shaped fiber and hybrid AuNPs–cubic silver oxide interface for ultrasensitive detection of gentamicin in real food samples

Gentamicin is an important pollutant in milk that causes harm to the human body. In this study, a plasmonic biosensor with a tapered multi-mode fiber (MMF) and four-core fiber (FCF) and multi-mode fiber (MMF) structure was developed. Localized surface plasmon resonance (LSPR) was stimulated by immobilizing gold nanoparticles (AuNPs) on the optical fiber probe surface. Cubic silver oxide (Ag₂O) was used to modify the fiber-optic probe by altering the dielectric environment around the AuNPs, which modulated the LSPR phenomenon, expanded the probe surface area, and enlarged the adhesion zone for gentamicin monoclonal antibodies, thereby enhancing the selectivity of the sensor. Transmittance experiments showed the sensor had a linear range of 15-55 nM, <i>LoD</i> = 5.84 nM. Tests on repeatability, stability, pH and selectivity confirmed its reliable performance; the results of these experiments demonstrate strong potential for practical food safety applications in detecting gentamicin levels in food.