Toxicity and magnetometry evaluation of the uptake of core-shell maghemite-silica nanoparticles by neuroblastoma cells

We present a study of the cellular uptake and the toxicity of core-shell maghemite-silica magnetic nanoparticles (MNPs) with a diameter of 9 nm. The uptake of the nanoparticles by mouse neuroblastoma 2a cells was studied quantitatively by Graphite Furnace Atomic Absorption Spectroscopy and SQUID magnetometry with good agreement between the methods on the amount of Fe oxide internalised by the cells. We were thus able to study the toxicity of the nanoparticles for well quantified MNP uptake in terms of nanoparticle density within the cell in the range of 1.7 x 105 to 1.72 x 107 MNPs per cell. At all the exposures tested (from 0.1 ng/mL to 100 µg/mL, for 24 hours), there was no significant variation of cell viability and growth rate, but studies of intracellular effects showed an increase in the amount of mitochondrial superoxide and increasing lysosomal activity due to exposure to MNPs (at 100 µg/mL). These results suggest that, under the most extreme conditions, we could begin to detect a disruption in ROS homeostasis which may lead to an impairment in antioxidant responses. Overall, the results demonstrate that the use of these MNPs, in a wide range of concentrations, is not toxic under our culture conditions.