Thermographic Detection and Analysis of the Temporal and Spatial Evolution of Temperature upon Optical Heating of Gold Nanorod Assembly Immobilized in Agar

Photoexcitation of the longitudinal surface plasmon resonance band of gold nanorods (AuNRs) in the near-infrared region has been widely employed in photothermal therapy. Generally, the temperature evolution of the surface of the object of interest reflects the photothermal efficiency. However, the temperature in the object interior may be higher than required and cause unwanted damage to the healthy cells or tissues in the vicinity of the unhealthy areas. In this work, agar served as a biomimicking tissue, and 1 mm³ AuNR agar assembly cubes were placed at different depths with respect to the agar surface and excited with an 808 nm continuous-wave laser or an 850 nm light-emitting diode light. The evolution of the surface temperature was monitored with an infrared thermographic camera and analyzed with a point heat source model. The concentric temperature change suggested that the sample was nonfluidic and that convection and mass flow could be excluded. The depths of the AuNR agar cubes could be determined and were consistent with the prepared depths. Thus, using the agar matrix and AuNRs with optical heating and monitoring, in combination with the point heat source model, is feasible for the analysis of the surface and interior temperature evolutions of the object and the further determination of the initial conditions of systems, such as the positions of the heat source, the injection power, and so on.