Sedimentation-Diffusion Behaviour of Nanoparticles

Abstract

Background The biological response of organisms exposed to nanoparticles is often studied in vitro using adherent monolayers of cultured cells. In order to derive accurate concentration-response relationships, it is important to determine the local concentration of nanoparticles to which the cells are actually exposed rather than the nominal concentration of nanoparticles in the cell-culture medium. In this study, we investigated the sedimentation–diffusion process of different sized and charged gold nanoparticles in vitro by evaluating their settling dynamics and by developing a theoretical model to predict the concentration depth-profile of nanoparticles in solution over time.Results Experiments were carried out in water and in cell-culture media at a range of controlled temperatures. The optical phenomenon of caustics was exploited to track nanoparticles in real-time in a conventional optical microscope without any requirement for fluorescent labelling that potentially affects the dynamics of the nanoparticles. The results obtained demonstrate that size, temperature, and the stability of the nanoparticles play a pivotal role in regulating settling dynamics of nanoparticles. For gold nanoparticles larger than 60 nm in diameter, the initial nominal concentration did not accurately represent the concentration of nanoparticles local to the cells.Conclusion Nanoparticles dynamics in solution regulate the amount of material at the cellular level and must be taken into account when evaluating the biological response of organisms. the theoretical model proposed in this study accurately described the settling dynamics of the nanoparticles and thus represents a promising tool to support the design of in vitro experiments and the study of concentration-response relationships.