Aqueous ammonia 28

Tetraethylortosilicate (TEOS), triethanolamine (TEAH₃), sodium hydroxide (NaOH), N-cetyltrimethylammonium bromide (CTAB), Pluronic 123 (P123), hydrochloric acid 37% (HCl), aqueous ammonia 28% (NH₄OH), trifluoroacetic acid (TFA), (3-aminopropyl)triethoxysilane (APTES), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC), rhodamine B (RhB), oleic acid (OA) and all the chemicals for the digestive fluids (bile salts included) were provided by Sigma (Sigma-Aldrich Química S.L., Madrid, Spain). Ethanol (extra pure), dimethyl sulfoxide (DMSO), acetonitrile (ACN) and acetone were purchased from Scharlab (Scharlab S.L., Barcelona, Spain). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) was provided by ThermoFisher (Thermo Fisher Scientific Inc., Madrid, Spain). Phosphate Buffer Solution (PBS), Dulbecco’s Modified Eagle’s Medium (DMEM), Fetal Bovine Serum (FBS), penicillin/streptomycin antibiotic (P/S), non-essential amino acids and all the needed mediums for cell culture were provided by Labclinics (Labclinics S.A., Barcelona, Spain).

Fluorescent SiO₂ NPs were synthesized as previously reported [34 (link)]. Briefly, N-1-(3-trimethoxysilylpropyl)-N′-fluoresceyl thiourea (FITC-APTMS) conjugate solution was prepared by dissolving 2 mg fluorescein isothiocyanate (FITC) (Sigma-Aldrich, St. Louis, MO, USA) in 1 mL anhydrous ethanol (Carlo Erba Reagents S.r.l., Milano, Italy) and immediately mixed with 10 µL of (3-Aminopropyl)trimethoxysilane (APTMS) (Sigma-Aldrich, St. Louis, MO, USA) under shaking at room temperature for 4 h in the dark. Under nitrogen atmosphere, 25 mL of ethanol was added to 1 mL of aqueous ammonia (28%) (Sigma-Aldrich, St. Louis, MO, USA) and stirred. Then, 950 µL Tetraethyl orthosilicate (TEOS) (Sigma-Aldrich, St. Louis, MO, USA) was mixed with the conjugate solution, and the reaction was stirred at 600 rpm at room temperature for a further 20 h in darkness. The resulting particles were washed three times by centrifugation and resuspension in EtOH using bath sonication and ultimately resuspended in EtOH to reach a final particle concentration of 10 mg/mL.