Porous Silicon Nanoparticle Photosensitizers for Singlet Oxygen and Their Phototoxicity against Cancer Cells

Porous Si nanoparticles, prepared from electrochemically etched single crystal Si wafers, function as photosensitizers to generate (1)O(2) in ethanol and in aqueous media. The preparation conditions for the porous Si nanoparticles were optimized to maximize (1) the yield of material; (2) its quantum yield of (1)O(2) production; and (3) its in vitro degradation properties. The optimal formulation was determined to consist of nanoparticles 146 ± 7 nm in diameter, with nominal pore sizes of 12 ± 4 nm. The quantum yield for (1)O(2) production is 0.10 ± 0.02 in ethanol and 0.17 ± 0.01 in H(2)O. HeLa or NIH-3T3 cells treated with 100 μg/mL porous Si nanoparticles and exposed to 60 J/cm(2) white light (infrared filtered, 100 mW/cm(2) for 10 min) exhibit ∼45% cell death, while controls containing no nanoparticles show 10% or 25% cell death, respectively. The dark control experiment yields <10% cytotoxicity for either cell type.