Endocytosis and Lack of Cytotoxicity of Alkyl-Capped Silicon Quantum Dots Prepared from Porous Silicon

Abstract

Freely-dissolved silicon quantum dots were prepared by thermal hydrosilation of 1-undecene at high-porosity porous silicon under reflux in toluene. This reaction produces a suspension of alkyl-capped silicon quantum dots (alkyl SiQDs) with bright orange luminescence, a core Si nanocrystal diameter of about 2.5 nm and a total particle diameter of about 5 nm. Previous work has shown that these particles are rapidly endocytosed by malignant cell lines and have little or no acute toxicity as judged by the standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for viability and the Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay for apoptosis. We have extended this work to the CACO-2 cell line, an established model for the human small intestinal mucosa, and demonstrate that neither acute nor chronic (14 days) toxicity is observed as judged by cell morphology, viability, ATP production, ROS production and DNA damage (single cell gel electrophoresis) at doses of 50–200 μ g mL − 1 . Quantitative assessment of the extent of uptake of alkyl SiQDs by CACO-2, HeLa, HepG2, and Huh7 cell lines by flow cytometry showed a wide variation. The liver cell lines (HepG2 and Huh7) were the most active and HeLa and CACO-2 showed comparable activity. Previous work has reported a cholesterol-sensitivity of the endocytosis (HeLa), which suggests a caveolin-mediated pathway. However, gene expression analysis by quantitative real–time polymerase chain reaction (RT-PCR) indicates very low levels of caveolins 1 and 2 in HepG2 and much higher levels in HeLa. The data suggest that the mechanism of endocytosis of the alkyl SiQDs is cell-line dependent.

Water-Soluble Silicon Quantum Dots toward Fluorescence-Guided Photothermal Nanotherapy

“…The photostability of SiQDs with alkyl termination in CACO-2 cells has been reported. 44 Cells having alkylated SiQDs of up to 50 μg/mL could still be detected after 14 days. The photostability of SiQDs could also be investigated by photobleaching studies.…”

“…Similar efforts have been studied in other papers. The photostability of SiQDs with alkyl termination in CACO-2 cells has been reported . Cells having alkylated SiQDs of up to 50 μg/mL could still be detected after 14 days.…”

Nano–bio interaction between human immunoglobulin G and nontoxic, near-infrared emitting water-borne silicon quantum dot micelles

“…[49][50][51] Phatvej et al demonstrated an endocytosis pathway for alkyl-capped silicon quantum dots using various cell lines, including HeLa. 52 According to the references, SiQDs/F127 micelles are taken up by HeLa and Fibroblast cells via endocytosis. Aer endocytosis, the micelle will be localized in the early endosome and later translocation to late endosome.…”

Silicon Quantum Dots: Synthesis, Encapsulation, and Application in Light-Emitting Diodes

“…A straightforward approach lately demonstrated to increase the water dispersibility and photostability of SiQDs requires encapsulation into mesoporous silica through a simple condensation reaction in which mesoporous silica dispersed in toluene is mixed with a SiQD solution in C 2 H 5 OH, followed by heating to 110 • C for reflux for 3 h. The resulting encapsulated SiQD has excellent hydrophilicity, good biocompatibility, low cytotoxicity, retains a high surface area, and exhibits better fluorescence stability in acidic solutions, making it ideally suited for biological applications (Huang et al, 2018;Phatvej et al, 2019). A procedure for obtaining SiQDs capped with an Si-C bonded alkyl layer by heating in an ultrahigh vacuum at 200 • C has been reported (Chao et al, 2007).…”