Ultrafast laser synthesis of NIR-absorbing Au-TiO₂ nanoagents for photothermal theranostics

Pure noble metal nanoparticles (NPs) are widely used as benchmarks in theranostic applications, such as photothermal cancer therapy. However, plasmon-mediated absorption of such NPs is typically confined to the visible range, resulting in poor light-to-heat conversion efficiency within the near-infrared (NIR) wavelengths matching biological transparency windows. Here, we report a rapid, single-step synthesis of NIR-absorbing Au-TiO₂ nanocomposites through femtosecond-laser modification of a commercial anatase TiO₂ nanopowder (P25) suspension containing tetrachloroauric acid. High-repetition-rate ultrashort laser irradiation yields, within minutes, core-satellite nanostructures (<100 nm) comprising an amorphous titania core decorated with Au nanoclusters. Comprehensive characterization confirms laser-induced modifications, which endow the product with strong NIR absorption in the first biological transparency window. Au-TiO₂ NPs exhibit a competitive photothermal conversion efficiency at low concentrations down to 10 μg/mL, low in vitro toxicity comparable to pristine P25 TiO₂ NPs, and efficient uptake by triple-negative breast cancer cells. Additionally, the nanocomposites demonstrate a drug-carrying capacity and compatibility with bio-visualizing molecules, highlighting their potential as a novel nanoagent for anticancer theranostics.