Quantifying the nanoscale “hot-spot” effect in aqueous suspensions of iron oxide photothermal nanoagents with photoacoustic spectroscopy – Hotspot

External stimulation of nanoparticles to deposit heat in biological tissues and induce a therapeutic effect can lead to macroscopic heating and/or the generation of nanoscale “hot spots”. Although there is an emerging interest in the “hot spot” effect, the nanometric scale makes it more difficult to measure for particles in solution. In this project, we propose to develop a method for quantitatively measuring the “hot spot” effect for optically absorbing nanoparticles used as photothermal therapy agents. The method is based on quantitative photoacoustic spectroscopy, which has already demonstrated its ability to assess the light-heat conversion efficiency through mesoscopic measurements on particle suspensions. We will validate the instrument on iron oxide-based photothermal nanoagents absorbing in the second transparency window of biological tissues. Various nanoparticle assemblies will be fabricated to modulate the hot-spot effect. Finally, the link between measurements in solution and therapeutic efficacy will be evaluated on cell cultures. This project will enable the development of an innovative and quantitative laboratory instrument, and pave the way for the design of agents maximizing the hotspot effect.