Photosensitized fluoroquinolones drive silver nanoparticle dissolution and synergistic toxicity: The role of reactive oxygen species.

Antibiotics and nanoparticles, frequently detected in aquatic environments, exhibit ubiquitous coexistence; however, the environmental implications of their interactions have not been adequately investigated. Failure to account for their interplay could result in significant underestimation of associated risks. In this study, fluoroquinolones (FQs) and silver nanoparticles (AgNPs) were chosen as model compounds, and Escherichia coli was used as a bioindicator, to investigate their synergistic toxicity and mechanism. It was elucidated that a photosensitization-driven mechanism by which FQs enhance AgNPs toxicity under sunlight exposure. We observed significant synergistic growth inhibition in co-exposure systems (synergy factor up to 7.68), surpassing the effects of individual agents. Photochemical analysis revealed that FQs accelerate AgNPs photo-corrosion via generation of reactive oxygen species (ROS), particularly triplet-state FQs (3FQs*) and singlet oxygen (1O2), which promote Ag+ release. Selective quenching experiments and electron paramagnetic resonance spectroscopy confirmed 3FQs* as the dominant oxidizing species, contributing up to 66.7 % of Ag+ release. Ag+ liberation exhibited strong correlations with both ROS generation rates (R² = 0.986) and bacterial growth inhibition (R² = 0.993). Density functional theory calculations revealed that FQs exhibit low excitation energy thresholds in their molecular orbitals, enabling efficient photoexcitation followed by strong adsorption interactions with AgNPs, facilitating photoinduced electron transfer from 3FQs* to AgNPs. These findings highlight a previously underappreciated ecotoxicological risk associated with antibiotics-AgNPs co-contamination in sunlit waters and underscore the need to incorporate light-mediated transformation processes in nanomaterial risk assessments.