Dual effects of cyanobacterial extracellular polymeric substances on the chemical transformations of silver nanoparticles driven by eco-corona formation.

As a result of their broad commercialization and diverse applications, silver nanoparticles (AgNPs) are being continuously released into environment. Once entering aquatic systems, AgNPs encounter various biomolecules, such as extracellular polymeric substances (EPS), giving rise to the formation of eco-corona. Proteins are known to interact strongly with nanoparticles, and mediate their environmental behavior, however, the role of polysaccharides, as the dominant component in microalgal EPS, remain largely understood. Herein, cyanobacterial EPS from Microcystis aeruginosa exhibited a concentration-dependent dual effect on the chemical transformations of AgNPs. At low concentrations, proteins in EPS strongly interacted with AgNPs, accelerating AgNPs dissolution via ligand-promoted processes. As EPS concentrations increased, polysaccharides were gradually involved after proteins saturation through glucuronic acid adsorption mediated by hydrogen bonding and van der Waals interaction with tryptophan-like structures. The enhanced aggregation of AgNPs decreased available surface area, thereby limiting interactions with dissolved oxygen and chloride ions, which ultimately suppressed dissolution and chlorination processes. Our findings demonstrated that acidic polysaccharides cooperated with proteins to play an essential, though previously overlooked, role in forming eco-corona and controlling AgNPs transformation processes, and advanced deeper understanding on nano-bio interactions and environmental fate of AgNPs in aquatic environments.