2.1.1. Synthesis of SiNPs

SiNPs used in this study were synthesized by the Stöber method as previously described by Liberman et al. [23]. Briefly, 200 mL ethanol (96%) and 36 mL deionized water were heated to 75 ◦C in a two-neck round-bottom flask attached to a reflux condenser. To this mixture, 10 mL of 25% aqueous ammonia was added and the system was equilibrated for 15 min. This was followed by the addition of 15 mL tetraethylorthosilicate (TEOS), and the reaction was vigorously stirred for 2 h at 500 rpm. The obtained silica dispersion was centrifuged for 1 h at 6000× *g* at 4 ◦C. The pellet was then washed three times with deionized water by centrifugation at 6000× *g* for 30 min. Then, the washed particles were suspended in ethanol (96%) to circumvent extensive particle agglomeration, and dried at 80 ◦C for 12 h.
