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

Abstract

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 mm 3 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 lightemitting 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.

Applications of time‐resolved step‐scan Fourier‐transform infrared spectroscopy in revealing the light‐initiated reactions in condensed phases

“…The femtosecond trainset absorption, reflectance, and transmittance have been employed to study the thermal energy transfer between the electron and the nanoparticle crystal, the acoustic vibration, and the thermalization with the environments within nanoseconds [117][118][119]. There are several slow methods to investigate the temperature evolution or thermal distribution of the environments, such as mechanical approaches using thermocouples [120,121], non-contact methods using nanobubble scattering [122], photoacoustic imaging [123], fluorescence polarization anisotropy [124], infrared thermography [125,126], tryptophan-based fluorescent thermometry [127][128][129], and so on. Interestingly, few experiments have investigated the temperature of the bare nanoparticles after the phonon thermalization in the nanoparticle within the nanosecondmicrosecond time domain.…”

Radiative Relaxation of Gold Nanorods Coated with Mesoporous Silica with Different Porosities upon Nanosecond Photoexcitation Monitored by Time-Resolved Infrared Emission Spectroscopy

“…24,25 Combining microscopy techniques provided spatial and temporal resolutions that benefited the investigation of the homogeneous and inhomogeneous effects of a single nanostructure, 26 such as the dynamics of plasmon wave packets of single gold nanorods, using an ultrafast timeresolved scanning near-field optical microscopy (SNOM) system 27 and the acoustic vibrations of single gold nanorods in different environments. 28 During the prolonged period for thermalization between the nanoparticles and surroundings upon pulsed or continuouswave excitation, the temperature evolutions of the surroundings containing the dispersed nanostructures can be probed with mechanical thermometers, such as thermocouples, 29,30 and spectroscopic thermometry methods such as infrared thermography, 31,32 the optoacoustic technique, 33,34 the intensity ratio between the anti-Stokes and Stokes of the Raman spectra of the substrate 35 or the capping layer, 36 fluorescence change of the aromatic residue tryptophan, 37,38 fluorescence shift of quantum dots, 39 and refractive index changes of the medium surroundings. 40 Regarding the temperatures of the nanoparticles themselves, anti-Stokes emission 41,42 has been utilized to probe the temperature of a single nanoparticle at the nanoscale, and time-resolved step-scan Fourier transform infrared (FTIR) spectroscopy has been used to probe the thermal radiative relaxation of a bunch of dried gold nanoparticles (AuNPs) 43 and gold nanorods (AuNRs) 44,45 coated with various molecules, such as methoxyl-poly-(ethyleneglycol)-thiol (mPEG), poly(styrenesulfonate) (PSS), and silica (SiO 2 ).…”