Influence of Surface Charge on the Functional Properties of Silica Nanoparticles and Cellular Toxicity

The effect of silica nanoparticles with a different surface charge on the cell viability of Caco-2 and RAW 264.7 cell lines was studied. Silica nanoparticles with narrow size distribution were prepared by Stobers method. These silica nanoparticles surface charge was varied from highly positive to highly negative, were single functionalized by APTES and multi functionalized by cysteine for amine and carboxyl groups. All other properties of the nanoparticles were kept constant. The unfunctionalized nanoparticles were used as control. Fourier Transform Infrared spectroscopy (FTIR) confirmed the presence of amine and carboxyl groups present on the surface of silica nanoparticles. The zeta potential measurements confirmed the successful modification of surface charge of silica nanoparticles in water. SEM images showed that the negatively charged, positively charged, and unfunctionalized nanoparticles with similar size and shape. MTT assay results indicated that the toxicity of SiO2 was cell type-dependent. CaCo-2 cells were highly resistant to nanoparticle treatment whereas RAW 264.7 (macrophages) predominantly charge dependent. The difference in toxicity could be attributed to the difference in the physiological function of each cell line. Among the three kinds of nanoparticles (negative, positive, and untreated), positively charged nanoparticles showed higher toxicity, which might be due to the attractive interaction between the negatively charged cell membrane and positively charged SiO2 nanoparticles.