Cytotoxicity control of silicon nanoparticles by biopolymer coating and ultrasound irradiation for cancer theranostic applications.

Silicon nanoparticles (SiNPs) prepared by mechanical grinding of luminescent porous silicon were coated with a biopolymer (dextran) and investigated as a potential theranostic agent for bioimaging and sonodynamic therapy. Transmission electron microscopy, photoluminescence and Raman scattering measurements of dextran-coated SiNPs gave evidence of their enhanced stability in water. In vitro experiments confirmed the lower cytotoxicity of the dextran-coated NPs in comparison with uncoated ones, especially for high concentrations of about 2 mg ml-1. Efficient uptake of the NPs by cancer cells was found using bioimaging in the optical transmittance and photoluminescence modes. Treatment of the cells with uptaken SiNPs by therapeutic ultrasound for 5-20 min resulted in a strong decrease in the number of living cells, while the total number of cells remained nearly unchanged. The obtained data indicate a 'mild' effect of the combined action of ultrasonic irradiation and SiNPs on cancer cells. The observed results reveal new opportunities for controlling the photoluminescent and sonosensitizing properties of silicon-based NPs for applications in the diagnostics and mild therapy of cancer.

Silicon Nanoparticles as Amplifiers of the Ultrasonic Effect in Sonodynamic Therapy.

The possibility of using mesoporous silicon nanoparticles as amplifiers (sensitizers) of therapeutic ultrasonic exposure were studied experimentally in vitro and in vivo. The combination of nanoparticles and ultrasound led to a significant inhibition of Hep-2 cancer cell proliferation and Lewis lung carcinoma growth in mice. These results indicated good prospects of using silicon nanoparticles as sensitizers for sonodynamic therapy of tumors.

Raman and fluorescence micro-spectroscopy applied for the monitoring of sunitinib-loaded porous silicon nanocontainers in cardiac cells.

Nanomaterials are a central pillar in modern medicine. They are thought to optimize drug delivery, enhance therapeutic efficacy, and reduce side-effects. To foster this technology, analytical methods are needed to validate not only the localization and distribution of these nanomaterials, but also their compatibility with cells, drugs, and drug release. In the present work, we assessed nanoparticles based on porous silicon (pSiNPs) loaded with the clinically used tyrosine kinase inhibitor sunitinib for their effectiveness of drug delivery, release, and toxicity in colon cancer cells (HCT 116 cells) and cardiac myoblast cells (H9c2) using Raman micro-spectroscopy, high-resolution fluorescence microscopy, along with biological methods for toxicological effects. We produced pSiNPs with a size of about 100 nm by grinding mesoporous silicon layers. pSiNPs allowed an effective loading of sunitinib due to their high porosity. Photoluminescence properties of the nanoparticles within the visible spectrum allowed the visualization of their uptake in cardiac cells. Raman micro-spectroscopy allowed not only the detection of the uptake and distribution of pSiNPs within the cells via a characteristic silicon Raman band at about 518-520 cm-1, but also the localization of the drug based on its characteristic molecular fingerprints. Cytotoxicity studies by Western blot analyses of apoptotic marker proteins such as caspase-3, and the detection of apoptosis by subG1-positive cell fractions in HCT 116 and MTT analyses in H9c2 cells, suggest a sustained release of sunitinib from pSiNPs and delayed cytotoxicity of sunitinib in HCT 116 cells. The analyses in cardiac cells revealed that pSiNPs are well tolerated and that they may even protect from toxic effects in these cells to some extent. Analyses of the integrity of mitochondrial networks as an early indicator for apoptotic cellular effects seem to validate these observations. Our study suggests pSiNPs-based nanocontainers for efficient and safe drug delivery and Raman micro-spectroscopy as a reliable method for their detection and monitoring. Thus, the herein presented nanocontainers and analytical methods have the potential to allow an efficient advancement of nanoparticles for targeted and sustained intracellular drug release that is of need, e.g., in chronic diseases and for the prevention of cardiac toxicity.

Effects of nanostructurized silicon on proliferation of stem and cancer cell.

In vitro experiments showed that stem and cancer cells retained their viability on the surface of porous silicon with 10-100 nm nanostructures, but their proliferation was inhibited. Silicon nanoparticles of 100 nm in size obtained by mechanical grinding of porous silicon films or crystal silicon plates in a concentration below 1 mg/ml in solution did not modify viability and proliferation of mouse fibroblast and human laryngeal cancer cells. Additional ultrasonic exposure of cancer cells in the presence of 1 mg/ml silicon nanoparticles added to nutrient medium led to complete destruction of cells or to the appearance of membrane defects blocking their proliferation and initiating their apoptotic death.

Evaluation of genotoxicity and reproductive toxicity of silicon nanocrystals.

Silicon crystal 2-5 nm nanoparticles in the form of 1-5-µ granules in water suspension were injected intraperitoneally in a single dose to male F(1)(CBA×C57Bl/6) mice or to outbred albino rats on days 1, 7, and 14 of gestation. Silicon crystal nanoparticles in doses of 5, 25, and 50 mg/kg exhibited no cytogenetic activity in mouse bone marrow cells after 24-h exposure and in doses of 5 and 25 mg/kg after 7 and 14-day exposure. A 24-h exposure to silicon nanoparticles in a dose of 5 mg/kg significantly increased DNA damage (detected by DNA comet assay) in bone marrow cells. In a dose of 50 mg/kg they considerably increased DNA damage in bone marrow and brain cells after exposure of the same duration. Silicon nanoparticles in doses of 5 and 50 mg/kg caused no genotoxic effects in the same cells after 3-h and in a dose of 5 mg/kg after 7-day exposure. Silicon crystal nanoparticles in a dose of 50 mg/kg caused death of 60-80% mice after exposure <24 h. Injected in a dose of 50 mg/kg on days 1, 7, and 14 of gestation, silicon crystal nanoparticles reduced body weight gain in pregnant rats and newborn rats at different stages of the experiment, but had no effect on other parameters of physical development of rat progeny and caused no teratogenic effects.

Biodegradation model of porous silicon nanoparticles.

Development of porous silicon-based drug delivery systems for theranostics requires a precise control of their biodegradation. Thus, we propose a model for the biodegradation of porous silicon nanoparticles (PSi NPs) based on a diffusion equation combined with Nernst-Brunner mass transfer equation describing the dissolution of silicon and formation of silicic acid (SA). The spatiotemporal distributions of PSi NP porosity and SA concentration were calculated. The model was successfully applied to fitting a great variety of experimental data on more than 10 factors influencing the PSi NP biodegradation kinetics, such as the morphology of PSi NPs, surface composition, properties of surrounding media and protective coating layer. Two principal regimes were found out for systems with either diffusion or dissolution dominating over each other. The results of simulations revealed the values of several important parameters, which are hard to be measured experimentally.

Laser-synthesized oxide-passivated bright Si quantum dots for bioimaging.

Crystalline silicon (Si) nanoparticles present an extremely promising object for bioimaging based on photoluminescence (PL) in the visible and near-infrared spectral regions, but their efficient PL emission in aqueous suspension is typically observed after wet chemistry procedures leading to residual toxicity issues. Here, we introduce ultrapure laser-synthesized Si-based quantum dots (QDs), which are water-dispersible and exhibit bright exciton PL in the window of relative tissue transparency near 800 nm. Based on the laser ablation of crystalline Si targets in gaseous helium, followed by ultrasound-assisted dispersion of the deposited films in physiological saline, the proposed method avoids any toxic by-products during the synthesis. We demonstrate efficient contrast of the Si QDs in living cells by following the exciton PL. We also show that the prepared QDs do not provoke any cytoxicity effects while penetrating into the cells and efficiently accumulating near the cell membrane and in the cytoplasm. Combined with the possibility of enabling parallel therapeutic channels, ultrapure laser-synthesized Si nanostructures present unique object for cancer theranostic applications.

Coherent anti-Stokes Raman scattering in silicon nanowire ensembles.

In this letter, we, for the first time, report on coherent anti-Stokes Raman scattering (CARS) spectroscopy of an ensemble of silicon nanowires (SiNWs) formed by wet chemical etching of crystalline silicon with a mask of silver nanoparticles. The fabricated SiNWs have diameter ranged from 30 to 200 nm and demonstrate both visible and infrared photolumine cence (PL) and spontaneous Raman signal, with their intensities depending on presence of silver nanoparticles in SiNWs. The efficiency of CARS in SiNW ensembles is found to be significantly higher than that in crystalline silicon. The results of CARS and PL measurements are explained in terms of resonant excitation of the electron states attributed to silicon nanoparticles.