Assembled Behavior of Noble Metal Nanoparticles Related to Capping Agents in Sol–Gel Process.

The assembly of noble metal nanoparticles (NPs) created using different capping agents was investigated in a sol–gel process. By controlling the hydrolysis and condensation of tetraethyl orthosilicate (TEOS), noble metal NPs were assembled and fixed permanently through the anisotropic growth of SiO₂ shell. Various morphological noble metal NP assemblies including single bead, dimer, and pearl-chain were fabricated by controlling the addition of TEOS. Noble metal NPs were homogenously coated with SiO₂ shell without using a bulk polymer or silane coupling agent as the surface primer. It is worth noting that the assembled noble metal NPs which stabilized by different stabilizers performed different UV-vis adsorption spectra. With increasing the length of assemblies, longitudinal Plasmon resonance band appears and can be tuned from visible to near-infrared. These assemblies could be applies in biomedicine area, particularly as biosensors, Raman-tag particles, and photothermal therapy.