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Silicon Quantum Dot Nanoparticles with Antifouling Coatings for Immunostaining on Live Cancer Cells

Tu, Chang-Ching, Chen, Kuang-Po, Yang, Tsu-An, Chou, Min-Yuan, Lin, Lih Y., Li, Yaw-Kuen
ACS Applied Materials & Interfaces 2016 v.8 no.22 pp. 13714-13723
antibodies, antifouling agents, biocompatibility, biodegradability, bovine serum albumin, cell viability, cytotoxicity, electrochemistry, energy, flow cytometry, fluorescein, fluorescence, fluorescent antibody technique, hydrophilicity, image analysis, isothiocyanates, milling, nanoparticles, neoplasm cells, neoplasms, nitric acid, photoluminescence, polyethylene glycol, quantum dots, silicon, solvents, water solubility
Fluorescent silicon quantum dots (SiQDs) have shown a great potential as antiphotobleaching, nontoxic and biodegradable labels for various in vitro and in vivo applications. However, fabricating SiQDs with high water-solubility and high photoluminescence quantum yield (PLQY) remains a challenge. Furthermore, for targeted imaging, their surface chemistry has to be capable of conjugating to antibodies, as well as sufficiently antifouling. Herein, antibody-conjugated SiQD nanoparticles (SiQD-NPs) with antifouling coatings composed of bovine serum albumin (BSA) and polyethylene glycol (PEG) are demonstrated for immunostaining on live cancer cells. The monodisperse SiQD-NPs of diameter about 130 nm are synthesized by a novel top-down method, including electrochemical etching, photochemical hydrosilylation, high energy ball milling, and “selective-etching” in HNO₃ and HF. Subsequently, the BSA and PEG are covalently grafted on to the SiQD-NP surface through presynthesized chemical linkers, resulting in a stable, hydrophilic, and antifouling organic capping layer with isothiocyanates as the terminal functional groups for facile conjugation to the antibodies. The in vitro cell viability assay reveals that the BSA-coated SiQD-NPs had exceptional biocompatibility, with minimal cytotoxicity at concentration up to 1600 μg mL–¹. Under 365 nm excitation, the SiQD-NP colloid emits bright reddish photoluminescence with PLQY = 45–55% in organic solvent and 5–10% in aqueous buffer. Finally, through confocal fluorescent imaging and flow cytometry analysis, the anti-HER2 conjugated SiQD-NPs show obvious specific binding to the HER2-overexpressing SKOV3 cells and negligible nonspecific binding to the HER2-nonexpressing CHO cells. Under similar experimental conditions, the immunofluorescence results obtained with the SiQD-NPs are comparable to those using conventional fluorescein isothiocyanate (FITC).