Thermal and optical characterization of SiO₂–Au composites with absorption in the near-infrared

Research in nanoscience has allowed the development of new nanomaterials and nanostructures. Nanoparticles, particularly those that combine two or more materials for improving their properties, are widely used in biomedicine, among these silica (SiO₂) and gold nanoparticles (AuNPs) have shown their potential. In this work functionalized SiO₂ spheres, AuNPs, and silica-gold (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, introduced in this work. 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. The results show that even though there were no noticeable changes in thermal diffusivity by attaching the AuNPs on the surface of SiO₂ spheres, optical properties are indeed enhanced, especially at 980 nm and 1064 nm in this case. Graphical abstract: [Figure not available: see fulltext.].