the brown Au-OSi@CS nanoparticles were obtained via centrifugation
and washed with water 3 times, and then redispersed in water
until use. Finally, the Au-OSi@CS suspension was heated to boil, and
afterward 1 mL of 1% H2PtCl6 and 2 mL of 1% citrate were added, followed
by the addition of 3 mL 0.2 M ascorbic acid, which acted as the
reduction of H2PtCl6 [28]. After the mixture was heated for 30 min
under stirring, black Pt-Au-OSi@CS nanoparticles were obtained.
The resulting solution was stalled for 3 h, and then it was centrifugated
repeatedly until the supernatant turned colorless. The
synthetic process of Pt-Au-OSi@CS is shown in Scheme 1.