Data from: Settling dynamics of nanoparticles in simple and biological media

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, the sedimentation–diffusion
process of different sized and charged gold nanoparticles has been
investigated 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. 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.