To deposit a shell
from silica on the Ag NPs and Au NPs cores, 2.5mL of
103M 3-aminopropyl trimethoxysilane was added to
500mL of the Ag NPs and Au NPs under vigorous
magnetic stirring. After 15 min, 20 ml of a 0.54wt%
sodium silicate solution with pH in the range 10–11 was
added, and then the resulting solution is allowed to stand for 1 week [32]. Excess silicate is then removed by several
centrifugation/redispersion steps.