Quantifying the photothermal efficiency of gold nanoparticles using tryptophan as an in situ fluorescent thermometer

Abstract

The photothermal efficiencies, denoting the efficiency of transducing incident light to heat, of gold nanoparticles of different diameters (∅ = 22-86 nm) were quantified upon exposure at 532 nm. The fluorescence of tryptophan at 300-450 nm upon 280 nm excitation serves as an in situ fluorescent thermometer to illustrate the evolution of the average temperature change in the heating volume of the nanoparticle solution. The fluorescence intensity decreases as the temperature increases, having a linear gradient of 2.05% fluorescence decrease per degree Celsius increment from 20 to 45 °C. The presence of gold nanoparticles at the nM level does not perturb the temperature-dependent fluorescence of tryptophan in terms of fluorescence contour and temperature response. The heating volume was defined by overlapping the collimated 532 nm laser (∅ = 0.83 mm) for exciting the nanoparticles and the 280 nm continuous-wave beam (∅ = 0.81 mm) for exciting tryptophan in a 2 mm × 2 mm square tube, and the fluorescence was collected perpendicularly to the collinear alignment. This method has satisfactory reproducibility and a sufficient temperature detectivity of 0.2 °C. The profiles of the average temperature evolution of the mixtures containing nanoparticles and tryptophan were derived from the evolution of fluorescence and analyzed using collective energy balancing. The relative photothermal efficiencies for different sizes of gold nanoparticles with respect to the 22 nm nanoparticle agree with those predicted using Mie theory. The employment of tryptophan as a fluorescent thermometer not only provides an in situ tool to monitor the photothermal effect of nanostructures but is also applicable to thermal imaging in biological applications.

Diameter effect of gold nanoparticles on photothermal conversion for solar steam generation

“…The size and morphology of Au NPs were two key factors for the photothermal conversion. 38 Here, we synthesized Au NPs with different sizes by a seeding growth method. The diameter effect of Au NPs on the photothermal conversion efficiency was studied using three accessible and reproducible methods through monitoring the changes of temperature, the vapor pressure and mass loss of the nanouids.…”

In Situ Photothermal Response of Single Gold Nanoparticles through Hyperspectral Imaging Anti-Stokes Thermometry

“…Optical methods based on temperature-sensitive probes are an appealing alternative. Organic dyes, rare-earth doped (nano)­crystals, or quantum dots may be used to report temperature through changes in their spectrum, intensity, lifetime, or anisotropy. , SERS also allows for temperature determination by monitoring the anti-Stokes to Stokes ratio for molecules in the vicinity of NPs, although suffering from weak signals, low photostability, and hard to calibrate wavelength-dependent plasmon-enhanced cross sections that make implementations difficult at the single-NP level. ,− Yet another optical method relies on determining the temperature from variations in the refractive index . However, retrieving accurate temperature measurements of plasmonic NPs using these methods is not always possible.…”

Influence of Morphological Homogeneity of Superspherical Gold Nanoparticles on Plasmonic Photothermal Heat Generation

“…The photothermal abilities of nanostructures are determined by the quantity of strongly absorbed incident light and resonant energy efficiently converted into heat energy; thus, most studies have experimentally or computationally investigated the photothermal conversion efficiency (PTCE) defined by the ratio of the heat generation to laser power loss or the ratio of absorption to extinction coefficient by varying the nanostructure size and shape. Jiang et al and Chiu et al found that the PTCE increases as the diameter of the gold nanoparticles (GNPs) decreases under a 532 nm continuous‐wave illumination . Guo et al investigated the PTCE for solar steam generation under solar illumination by measuring the temperature change, vapor pressure, and mass loss of nanofluids .…”

“…Jiang et al and Chiu et al found that the PTCE increases as the diameter of the gold nanoparticles (GNPs) decreases under a 532 nm continuous-wave illumination. [17,18] Guo et al investigated the PTCE for solar steam generation under solar illumination by measuring the temperature change, vapor pressure, and mass loss of nanofluids. [9] In the case of anisotropic nanostructures, Mackey et al reported that the optimum size of gold nanorods (GNRs) is 28 nm in length and 8 nm in width considering the PTCE, electric field, and distance between the particles.…”