Effects of agglomeration on in vitro dosimetry and cellular association of silver nanoparticles†
Agglomeration of nanoparticles (NPs) in cell culture media can alter their physicochemical properties and colloidal behaviour, which may affect their cellular association and cytotoxicity. Herein, we investigated the impact of agglomeration of silver NPs on their effective dose and cellular association under various in vitro assay conditions. Hydrodynamic sizes, zeta potentials, and effective densities of agglomerates were characterized for two different types of positively charged silver NPs with nominal core sizes of 60 nm and 100 nm. Then, three different dose metrics (administered, effective, and cellular doses) under upright and inverted exposure configurations were compared with the measured physicochemical properties and colloidal behaviours. Changes in the agglomeration characteristics, such as an increment in the hydrodynamic size and a decrement in the effective density, assisted the sedimentation and reduced the diffusion of NPs, leading to a higher effective dose and cellular association in the upright configuration than in the inverted configuration. From the comparison between the two sizes, we have observed that agglomerates of NPs with smaller core diameters could be less stably suspended in the biological media and thus, have higher effective doses and cellular association than agglomerates of NPs with larger core sizes, depending on their agglomeration process. Therefore, the agglomeration characteristics, rather than the intrinsic properties of the bare NPs, seem to have a more important role in determining the effective dose and cellular association of NPs and would be more relevant to understanding cell–nanoparticle interactions and their resultant cytotoxicity.