In vitro cytotoxicity of porous silicon microparticles: effect of the particle concentration, surface chemistry and size.

We report here the in vitro cytotoxicity of mesoporous silicon (PSi) microparticles on the Caco-2 cells as a function of particle size fractions (1.2-75 microm), particle concentration (0.2-4 mg ml(-1)) and incubation times (3, 11 and 24 h). The particle size (smaller PSi particles showed higher cytotoxicity) and the surface chemistry treatment of the PSi microparticles were considered to be the key factors regarding the toxicity aspects. These effects were significant after the 11 and 24 h exposure times, and were explained by cell-particle interactions involving mitochondrial disruption resulting from ATP depletion and reactive oxygen species production induced by the PSi surface. These events further induced an increase in cell apoptosis and consequent cell damage and cell death in a dose-dependent manner and as a function of the PSi particle size. These effects were, however, less pronounced with thermally oxidized PSi particles. Under the experimental conditions tested and at particle sizes >25 microm, the non-toxic threshold concentration for thermally hydrocarbonized and carbonized PSi particles was <2 mg ml(-1), and for thermally oxidized PSi microparticles was <4 mg ml(-1).