Synthesis of pure silica nanoparticles.

Silica nanoparticles (~300 nm) were synthesized by the well-established stöber method.³² 50 mL ammonium solution was made by mixing 9 mL ammonium hydroxide (25-28 wt%), 16 mL ethanol, and 25 mL deionized H₂O. This solution was swiftly added to 50 mL of 0.4 M TEOS ethanol solution under vigorous stirring. After reacting for 2h, the particles were centrifuged and washed three times with ethanol to collect monodisperse silica nanoparticles. TEM indicated that the average particle size was approximately 300 nm.