Experimental modelling of heating and local field enhancement by iron oxide nanoparticles upon laser excitation

Significance Local determination of the iron oxide nanoparticles (IONPs) temperature during laser heating is important in the aspect of laser phototherapy. Approach We have carried out theoretical modeling of local EM field enhancement and heating under the laser action near individual IONPs and ensembles of NPs with different sizes of the magnetic core and different content of iron oxide in them. To experimental determine the temperature of IONPs water colloids, we used fluorescence thermometry based on rhodamine B (RhB) fluorescence lifetime. Results Local EM field enhancement and heating strongly depend on the NPs shape and distance between them. In the case of anisotropic NPs, a significant change in the spatial distribution of the EM field near the NPs surface was observed. The local heating of NPs in an ensemble reaches sufficiently higher values, the relative change was about 35°С for Fe2O3 NPs. Nevertheless, all the studied IONPs water colloids showed heating by no more than 15°C. Conclusions Significant enhancement of the local field occurs in IONP pairs and ensembles. The heating temperature of the ensemble depends on the thermal conductivity of the medium, in which the heat dissipation depends.