Capping drives the behavior, dissolution and (eco)toxicity of silver nanoparticles towards microorganisms and mammalian cells

Surface coating plays a fundamental role in driving silver nanoparticle (AgNP) toxicity towards cells, but no clarity exists on the mechanism behind it. AgNPs with two different capping agents, citrate and l-cysteine (citLcys) and sodium-3-mercapto-1-propanesulfonate (3MPS), developed as sensors for metal ions in water (e.g., Hg(ii) and Ni(ii)), were investigated in terms of (eco)toxicity towards bacteria (Escherichia coli), microalgae (Raphidocelis subcapitata and Phaeodactylum tricornutum) and mammalian cells (HeLa and L929). After 72 h of incubation, Ag ion dissolution in algal media was negligible (<1% of nominal AgNP concentration) for both batches. Suspension in protein-rich media showed the formation of a protein corona around AgNPcitLcys as opposed to AgNP3MPS, which was confirmed by dynamic light scattering (DLS) analysis, transmission electron microscopy (TEM) and one-dimensional polyacrylamide gel electrophoresis (1D-PAGE). Low toxicity was observed for both AgNPs towards microalgae (>= 5 mg L-1) and E. coli (>= 256 mg L-1) and no effect was observed on HeLa and L929 cells. However, the responses suggest that citLcys coating might trigger the onset of a nano-size related toxicity as opposed to 3MPS, whose toxicity mainly relies on dissolution. Our findings show how surface coating rules AgNP interaction with biomolecules and drives AgNP (eco)toxicity towards cells, thus influencing exposure outcome.