Enhanced specific absorption rate in silanol functionalized Fe3O4 core-shell nanoparticles: study of Fe leaching in Fe3O4 and hyperthermia in L929 and HeLa cells.

Core-shell Fe3O4-SiO2 magnetic nanoparticles (MNPs) have been synthesized using a simple synthesis procedure at different temperatures. These MNPs are used to investigate the effect of surface coating on specific absorption rate (SAR) under alternating magnetic field. The temperature achieved by silica coated Fe3O4 is higher than that by uncoated MNPs (Fe3O4). This can be attributed to extent of increase in Brownian motion for silica coated MNPs. The sample prepared at optimized temperature of 80°C shows the highest SAR value of 111W/g. It is found that SAR value decreases with increase in shell thickness. The chemical stability of these samples is analyzed by leaching experiments at pH 2-7. The silica coated samples are stable up to 7 days even at pH 2. Biocompatibility of the MNPs is evaluated in vitro by assessing their cytotoxicity on L929 and human cervical cancer cells (HeLa cells) using sulforhodamine-B assay. Their hyperthermic killing ability is also evaluated in HeLa cells using the same method. Cells treated with MNPs along with induction heating show decrease in viability as compared to that without induction heating. Further, cell death is found to be ∼55% more in cells treated with silica coated MNPs under induction heating as compared to untreated control. These results establish the efficacy of Fe3O4-SiO2 prepared at 80°C in killing of tumor cells by cellular hyperthermia.