Monodispersed, nanosized gold-mesoporous silica nanospheres in the size range 80–280 nm with specific optical properties are prepared in two steps: i) controlled aggregation of gold nanoparticles (GNP) in nanoclusters embedded in a uniform coating of amorphous silica, and ii) development of a porous regular and ordered silica shell by pseudomorphic transformation of the external layer. By careful manipulation of the synthesis variables, i.e., the concentration of co-solvent, surfactant and alkali, it is possible to obtain nanoparticles with controlled morphological and textural characteristics and desired optical behaviour. An optimized sample with most of the nanoparticles containing a multinucleus core made of 10 or more GNP shows a strong absorption cross-section in the near-infrared (NIR) region and a significant photothermal effect when irradiated with a λ = 808 nm laser diode module.
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