80 °C) with stirring at 590 rpm for 30 minutes. Subsequently, 90 µmol of TEOS in 100 µL of ethanol were added at a rate of 0.8 mL/min, while the heating and stirring were continued for another 3 h. The particles were then cooled down, washed by three cycles of centrifugation (14k rcf, 15 min, 25 °C) and ultrasonic redispersion (30 s), once with water (5 mL) and twice with ethanol (5 mL).