Thermal and optical characterization of SiO₂ spheres decorated with gold nanoparticles

Research in nanoscience has allowed the development of nanomaterials and nanostructures which are useful in medical areas. These have been used for the improvement of equipment and the developing of methodologies for diagnostics and treatment of diseases. Nanoparticles, particularly those that combine two or more materials for improving their properties, are widely used in biomedicine, among these SiO₂ and AuNPs nanoparticles have shown their potential. In this work-functionalized SiO₂ spheres, gold nanoparticles (AuNPs), and SiO₂–Au complexes were synthesized. Thermal diffusivity and optical absorption coefficient, at selected wavelengths in the NIR region, were measured for the different colloidal solutions using novel photopyroelectric methodologies. SiO₂ spheres and AuNPs showed absorptions below 700 nm while the SiO₂–Au complexes showed a broad absorption band in the NIR region, as measured by conventional spectroscopy. This fact indicates an enhancement in light absorption of SiO₂ by the attaching of AuNPs on their surface and this was quantified by the pyroelectric technique introduced in this work. The results show that even though there were no noticeable changes in thermal diffusivity by attaching the gold nanoparticles on the surface of SiO₂ spheres, optical properties are indeed enhanced, especially at 980 nm and 1064 nm in this case.