Nanoparticles will soon be used as tiny shuttles to deliver genes to cells and drugs to tumors in a more targeted way than was possible in the past.
But as the scientists prepare to use the nanoparticles in medicine, concerns have arisen about their potential toxicity.
Studies of both the applications of nanoparticles and their toxicity rely on the ability of scientists to quantify the interaction between the nanoparticles and cells, particularly the uptake (ingestion) of nanoparticles by cells.
In the standard laboratory tests of the biological activity of nanoparticles, cells are plated on the bottom of a dish and culture medium containing nanoparticles is poured on top of them.
It seems straightforward enough. But recently Washington University in St. Louis scientist Younan Xia started to worry about the in vitro experiments his lab was doing with gold nanoparticles.
What if the cells were upside down, he wondered? Would that make a difference? Would it change their uptake rate?
Xia’s lab tested gold nanospheres of three sizes, nanocages of two edge lengths, and nanorods, some with surface coatings that picked up serum proteins in solution and others coated with a chemical that acts as an antifouling agent.
After the cells were incubated in the nanoparticle-bearing medium, the concentration of the nanoparticles in the medium was measured spectroscopically and the number of particles each cell had taken up was calculated from the difference in the concentrations.
In the literature, Xia says, there are reports that the cellular uptake of nanoparticles depends on the nanoparticles’ size, shape and surface coating.
His lab’s experiments showed that these characteristics are secondary, relevant only insofar as they affect the sedimentation and diffusion velocities of the nanoparticles.
For small, light particles, there was no disparity between the cells in the upright and the upside-down configurations. In the case of larger, heavier particles, however, sedimentation dominated, and the upright cells took in more nanoparticles than the upside-down cells.
“All earlier work may need to be re-evaluated to account for the effects of sedimentation on nanoparticle dosimetry,” the authors conclude.
“It’s no different from medicines that have to be shaken to suspend a powder in a water. If you don’t shake the bottle,” Xia says, “you end up under- or overdosing yourself.”
Contact: Diana Lutz firstname.lastname@example.org 314-935-5272 Washington University in St. Louis