Original Article
Studies of silicon nanoparticles uptake and biodegradation in cancer cells by Raman spectroscopy

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Abstract

In-vitro Raman micro-spectroscopy was used for diagnostics of the processes of uptake and biodegradation of porous silicon nanoparticles (SiNPs) in breast cancer cells (MCF-7 cell line). Two types of nanoparticles, with and without photoluminescence in the visible spectral range, were investigated. The spatial distribution of photoluminescent SiNPs within the cells obtained by Raman imaging was verified by high-resolution structured-illumination optical microscopy. Nearly complete biodegradation of SiNPs inside the living cells was observed after 13 days of the incubation. The results reveal new prospects of multi-modal visualization of SiNPs inside cancer cells for theranostic applications.

Graphical Abstract

Left: Schematic representation of SiNPs biodegradation processes: (I) localization of SiNPs on the cell membrane; (II) penetration of SiNPs in the cytoplasm with partial solubility of the nanoparticles; (III) strong dissolution of SiNPs after 10-13 days within the cell body.

Right: Raman spectra of NL-SiNPs for different incubation times: 9 h, 48 h and 13 days of incubation depicted in red, blue and green, respectively. Inset: corresponding xz-cross-section of Raman spectroscopy images of MCF-7 cells cultivated with NL-SiNPs.

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Section snippets

Nanoparticles formation

Heavily boron-doped (doping level of 1020 cm 3; specific resistivity of 0.005 Ω*cm) 4-inch crystalline silicon (c-Si) wafers with crystallographic orientation of (100) were used. Photoluminescent SiNPs (PL-SiNPs) were formed by using metal-assisted wet-chemical etching (MAWCE) to fabricate photoluminescent Si nanowires (PL-SiNWs) followed by their fragmentation by using in an ultrasound bath (37 kHz, 90 W). The MAWCE method is based on a two-step process, as previously reported.44 First, silver

Structural analysis of silicon nanostructures

Figure 1, A and B shows typical scanning electron microscopy (SEM) cross-sectional micrographs of PL-SiNWs and NL-PSi layers, respectively. The PL-SiNWs look as quasi-ordered arrays with preferential orientation along the [100] crystallographic direction. The depth of layers of PL-SiNWs and NL-PSi was about 30 μm and 60 μm, respectively. The diameter of the SiNWs was in the range of 150-300 nm, and remained constant over the whole length of SiNWs. The NL-PSi layers consist of a network of silicon

Discussion

Based on the performed investigations the model of SiNPs uptake and biodegradation by cancer cells is proposed and schematically represented in Figure 7. During the first step of incubation SiNPs are localized on the cell membrane starting to penetrate into the cell after 5-9 h (Stage I in Figure 7). Subsequent 24 h of incubation leads to the efficient distribution of SiNPs within the cell cytoplasm and on the nuclear periphery. Partial biodegradation of SiNPs can be observed (Stage II in Figure 7

Acknowledgements

The authors thank Dr. Reuter and Mrs. Shestaeva for their help during the experiments.

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    In the article “Studies of Silicon Nanoparticles Uptake and Biodegradation in Cancer Cells by Raman Spectroscopy” no conflicts of interest are presented.

    This work was supported by the German Federal Ministry of Education and Research under Grant No. 01DJ13010 and Baltic Sea Research Network “NanoPhoto” (Grant No. 01DS14017), by the scientific project No. 13 N12166 and “QuantiSERS” and “Jenaer Biochip Initiative 2.0” of “InnoProfile Transfer – Unternehmen Region“. The photoluminescence study was supported by the Russian Science Foundation (Grant No. №14-50-00029). L.A.O. greatly acknowledges the financial support of the joint program of MSU-DAAD “Vladimir Vernadsky”.

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