Gold nanolayer-encapsulated silica particles synthesized by surface seeding and shell growing method: near infrared responsive materials.

Gold nanolayer-encapsulated silica particles whose optical resonance is located in 750-900 nm spectral region were synthesized by combining Sn (tin)-surface seeding and a shell growing process. The synthesized composite particles can be potentially used in wide biological fields, due to biocompatibility and a well-known bioconjugation technique of gold layer. Sn atoms, which can act not only as a catalytic surface for reduction of gold but also as a linker between silica surface and gold nanoparticles, were chemically deposited on hydroxylated silica particles. Then, we introduced another reductant with gold chloride in order to produce a multilayer of Au shell. In the process, Au shells grew by the reduction of additional gold ions on the Sn-functionalized silica surface and resulted in the subsequent coalescence and growth of the deposited gold nanoparticles. Finally, a complete gold nanoshell was formed on the silica surface by the one-step method, without a repeated coating process. The deposition of a gold nanolayer on the silica particles was easily controlled by the concentration ratio of Sn-functionalized silica particles and gold chloride solutions. Transmission electron microscopy (TEM) images and optical extinction spectra clearly showed that gold nanolayers were successfully deposited on the silica surface by the novel method. As the gold colloids attached on the silica surface grew, their optical plasmon peak became red-shifted until complete a gold shell was formed. After the gold shell was completed, the optical plasmon resonance became blue-shifted and the extinction spectra were functions of a relative ratio of the core to shell thickness.

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