Abstract-Quantifying the photothermal conversion efficiency of plasmonic nanoparticles by means of terahertz radiation

APL Photonics

 H. Breitenborn^,   J. Dong^,  R. Piccoli^,   A. Bruhacs^,   L. V. Besteiro^,  , Z. M. Wang^,   A. O. Govorov^,   L. Razzari^,   F. Vetrone^,   R. Naccache^,  R. Morandotti

(a) Schematic diagram of THz temperature measurements based on a THz-TDS system set in reflection geometry. The 786-nm NIR beam used to plasmonically heat the GNR dispersions is overlapped with the THz focusing spot. The power of the NIR illumination transmitted through the cuvette is recorded with a power meter. The inset depicts the THz raster-scans of the front- and back-side of the cuvette. During the scanning process, the THz beam is fixed and the cuvette moves together with the IR beam pixel-by-pixel. (b) Example of a recorded THz signal reflected from the cuvette. The well-separated first and second echoes after sparse deconvolution are also plotted, in which the influence of the “ringing” due to the ambient water vapor is eliminated. (c) Temperature-dependent reflectivity of the second THz echo as a function of temperature for GNR10. (d) Calibration curves featuring a linear relationship between THz amplitude and temperature for each of the GNR dispersions.

https://aip.scitation.org/doi/abs/10.1063/1.5128524

The accurate determination of the photothermal response of nanomaterials represents an essential aspect in many fields, such as nanomedicine. Specifically, photothermal cancer therapies rely on the precise knowledge of the light-to-heat transfer properties of plasmonic nanoparticles to achieve the desired temperature-induced effects in biological tissues. In this work, we present a novel method for the quantification of the photothermal effect exhibited by nanoparticles in aqueous dispersions. By combining the spatial and temporal thermal dynamics acquired at terahertz frequencies, the photothermal conversion efficiency associated with the geometry of the plasmonic nanoparticles can be retrieved in a noncontact and noninvasive manner. The proposed technique can be extended to the characterization of all those nanomaterials which feature a temperature-dependent variation of the refractive index in the terahertz regime.