Surface coatings regulate the biodynamics and trophic transfer of silver nanoparticles: insights from Au@Ag core–shell nanoparticles

Silver nanoparticles (AgNPs) are widely used in industrial production and daily life, and their potential risks to aquatic environments deserve further attention. However, contributions of AgNPs and their released ions in the biodynamic processes within aquatic organisms remained largely unknown. To address this, this study fabricated various Au@AgNPs with different surface coatings to clarify key factors controlling the biodynamics of AgNPs under direct exposure in the water phase versus indirect exposure through the food chain (Escherichia coli–Tetrahymena thermophila). Au@AgNPs, a core–shell material, could well distinguish the bioaccumulation and transfer processes of particulate Ag and released Ag⁺. It is demonstrated that surface coating significantly influenced the biodynamics and trophic transfer of Au@AgNPs by regulating their surface charge. In water-phase exposure, surface coatings did not directly alter the internalization and excretion processes of AgNPs. Instead, they significantly modulated the dissolution behavior of the internalized particles and excretion rate of released Ag⁺ to induce the discrepancies in Ag accumulation ultimately. During trophic transfer, ethylene imine polymer-coated Au@AgNPs transferred from E. coli to T. thermophila in relatively intact particle form, exhibiting the highest relative transfer efficiency for NPs. In contrast, polyvinylpyrrolidone-Au@AgNPs showed the lowest transfer efficiency for both Ag and NP, indicating lower bioavailability, reduced transformation, and higher excretion efficiency. In conclusion, this study demonstrates that surface coating modulates AgNP biodynamics and transport processes in aqueous exposure and trophic transfer pathways by itself and regulating surface charge. When assessing nanomaterial ecological risks, it is essential to consider both the differential behavior of particulate and ionic forms and the potential amplification effects through trophic transfer.