Fabrication of Core-Shell Nanoparticles

The fabrication scheme for core-shell nanoparticles was adapted from work done by Lee and Meisel and Ung et al. Silver nitrate (99.998%), hydrogen tetrachloro-aurate(III) (99.999%), sodium citrate dihydrate (99+%), (3-aminopropyl)trimethoxysilane (97%), and sodium trisilicate solution (27%) were used. Absolute ethanol was used for quenching the Si02 shell growth. In all cases, the metallic core of the core-shell nanoparticle was synthesized before growing the dielectric shell. 

The Ag nanotriangle synthesis outlined in section 2.2.1 was one of the two ways that the metallic Ag cores were fabricated. The second Ag core fabrication method began with the treatment of all glassware with aqua regia (3 1 HCkHNOj) followed by a thorough rinse with ultrapure water (18.2 MQ cm ). Ninety mg of silver nitrate was 

The colloid solutions described above (Ag nanotriangles, citrate-reduced Ag, and citrate-reduced Au) were dialyzed against pH=5 ultrapure water for 48 hours before further modification. Based on the known size and density of the metallic cores, 1 mM aqueous (3-aminopropyl)trimethoxysilane (390 iL) was added to 10 mL of the dialyzed colloid solution. After 15 minutes, the pH of the colloid/(3-aminopropyl)trimethoxy-silane solution was raised to 11.5 by adding aqueous potassium hydroxide. Finally, the silica shell began to form after 27% sodium silicate (2.1 xL) was added to the basic solution. Quenching of the shell growth was accomplished by adding 40 mL of absolute ethanol to the nanoparticle solution. 

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