Synthesis and cytotoxicity of silicon nanoparticles with covalently attached organic monolayers

A series of highly monodisperse silicon nanoparticles (Si NPs) with either positively (amine), neutral (azide) or negatively (carboxylic acid) charged covalently attached organic monolayers were synthesized and investigated for their cytotoxicity. Infrared data confirmed the presence of these covalently attached surface groups. The Si NPs were characterized by absorption and fluorescence spectroscopy. The cytotoxicity was investigated in Caco-2 cells by determining the cell viability and proliferation. The IC50 values for the Si NPs ranged from 20 mu g/l for the amine-terminated Si NPs, via 550-850 mu g/l for the azide-terminated Si NPs to non-toxic (no measureable IC50) for the carboxylic acid-terminated Si NPs. These results indicate a trend in cytotoxicity, depending on surface charge, i.e., that positively charged Si NPs are more cytotoxic than negatively charged Si NPs. Interestingly, it appeared that the cytotoxicity of the Si NP-NH2 depends strongly on the presence of fetal calf serum in the medium.