Interfacial Interactions between Escherichia coli and Polystyrene Nanoplastics: a Physicochemical Perspective.

Nanoplastics are increasingly recognized as emerging environmental contaminants, yet the physicochemical mechanisms governing their interactions with bacterial cells remain insufficiently understood. In this study, we investigated the interactions between Gram-negative Escherichia coli and polystyrene nanoparticles (PS and PS-NH2; 100 and 200 nm) using electrophoretic light scattering (ELS), Fourier-transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). Zeta potential measurements revealed concentration-, pH-, and time-dependent shifts in the electrokinetic behavior of bacteria-nanoparticle mixtures, reflecting composite signals arising from nanoparticle attachment and surface-level interactions rather than direct measurements of bacterial surface charge. FTIR and AFM analyses confirmed nanoparticle surface adhesion and localized envelope perturbations; however, evidence for nanoparticle penetration remained indirect and subject to methodological limitations. Microbiological assays showed growth inhibition at nanoparticle concentrations ≥50 μg/mL, but no bactericidal activity was conclusively confirmed under the applied conditions. Overall, the results demonstrate that polystyrene nanoparticles induce measurable physicochemical and sublethal biological effects on E. coli without reaching cytotoxic thresholds, underscoring the importance of cautious interpretation when linking nanoparticle-induced surface perturbations to biological outcomes.