Effects of systematic variation in size and surface coating of silver nanoparticles on their in vitro toxicity to macrophage RAW 264.7 cells

In literature, varying and sometimes conflicting effects of physicochemical properties of NPs are reported on their uptake and effects in organisms. To address this, small and medium sized (20 and 50 nm) AgNPs with specified different surface coating/charges were synthesized and used to systematically assess effects of NP-properties on their uptake and effects in vitro. AgNPs were fully characterized for charge and size distribution in both water and test media. Macrophage cells (RAW 264.7) were exposed to these AgNPs at different concentrations (0 – 200 µg/mL). Uptake dynamics, cell viability, induction of tumor necrosis factor (TNF)-α, adenosine triphosphate (ATP) production and reactive oxygen species (ROS) generation were assessed. Microscopic imaging of living exposed cells showed rapid uptake and subcellular cytoplasmic accumulation of AgNPs. Exposure to the tested AgNPs resulted in reduced overall viability. Influence of both size and surface coating (charge) was demonstrated, with the 20 nm sized AgNPs and BSA coated (negatively charged) AgNPs being slightly more toxic. On specific mechanisms of toxicity (TNF-α and ROS production) however, the AgNPs differed to a larger extent. The highest induction of TNF-α was found in cells exposed to the negatively charged AgNP_BSA, both sizes (80x higher than control). ROS induction was only significant with the 20 nm positively charged AgNP_Chit.