Porous silicon nanoparticle photosensitizers for singlet oxygen and their phototoxicity against cancer cells

Abstract

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.

Figure 1

Time course of the absorption spectrum of the singlet oxygen indicator DPBF with porous Si nanoparticles (PSiNP) (a) in the presence of and (b) in the absence of light. Solution measurements were obtained in air-saturated ethanol. (c) Decay curves of the (background-corrected) 410-nm absorption bands from (a) and (b). (d) Decay curves of the (background-corrected) 410-nm absorption band from DPBF in irradiated solutions containing PSiNP, in either air-saturated or N₂-saturated solutions.

Figure 2

Increase in fluorescence intensity of SOSG endoperoxide as a function of irradiation time in the presence of SOSG alone, SOSG with RB and SOSG with porous Si nanoparticles (PSiNP) in air and in N₂ saturated solution, respectively.

Figure 3

Photoinduced toxicity exhibited by (a) HeLa cells and (b) NIH-3T3 cells treated with porous Si nanoparticles. The medium containing the porous Si nanoparticles (PBS buffer) was replaced with cell growth medium (RPMI-1640 medium supplemented with 10% FBS) immediately after irradiation. Cell viability quantified by MTS assay. Illumination was accomplished with a (IR filtered) halogen lamp. Each data point represents the mean of three independent experiments.

Figure 4

Phase contrast microscope images of HeLa cells treated with (a) PBS in the dark for 10 min (dark control), (b) 100 µg/mL porous Si nanoparticles (PSiNP) in the dark for 10 min, (c) PBS under 60 J/cm² light irradiation for 10 min (light control), and (d) 100 µg/mL PSiNP under 60 J/cm² light irradiation for 10 min. The scale bars are 50 µm.

Figure 5

Phototoxicity exhibited by (a and c) HeLa cells and (b and d) NIH-3T3 cells treated with porous Si nanoparticles. In these experiments, the cells were not rinsed post-irradiation as in Figure 3; instead, the cells were allowed to incubate with the nanoparticles in the culture medium for 24 h post-irradiation. In (a) and (b), the cells were irradiated with an (IR filtered) halogen lamp; in (c) and (d) the cells were irradiated with a blue LED panel (λ_max = 458 nm). The medium containing the porous Si nanoparticles was RPMI 1640 medium that did not contain FBS. Note the lower light flux and lower concentration of porous Si nanoparticles in this figure relative to Figure 3 and Figure S5. Cell viability quantified by MTS assay. Each data point represents the mean of three independent experiments.