Size-Dependent Photothermal Conversion Efficiencies of Plasmonically Heated Gold Nanoparticles

Abstract

We report the light-to-heat energy transfer efficiencies of gold nanoparticles with variable sizes by assessing the temperature profiles of laser-activated particle suspensions in water. Gold nanoparticles with sizes ranging from 5 to 50 nm were synthesized by chemical reduction methods using sodium borohydride, sodium citrate, or hydroquinone as reducing agents. As-synthesized gold nanoparticle solution (1 mL) was loaded into a quartz cuvette and exposed to a CW green laser (532 nm). Heat input into the system by energy transfer from nanoparticles equals heat dissipation at thermal equilibrium. The transducing efficiency was then determined by plotting temperature increase as a function of laser power extinction. The efficiency increases from 0.650 ± 0.012 to 0.803 ± 0.008 as the particle size decreases from 50.09 ± 2.34 to 4.98 ± 0.59 nm, respectively. The results indicate that the photothermal properties of gold nanoparticles are size-tunable, and the variation of efficiency can be correlated to the absorption/extinction ratios calculated by Mie theory for different particle sizes. We further expanded our Mie theory calculations of absorption/extinction ratios to a broader range of diameters and wavelengths. These studies are crucial for practical applications of gold nanoparticles in nanotechnology and bioengineering, such as enhancing the treatment efficiency of laser surgery.

Laser heating of metallic nanoparticles for photothermal ablation applications

“…It was demonstrated that the photothermal conversion efficiency of AuNP decreased from 0.8 to 0.65 when the diameter of AuNP increased from 5nm to 50 nm, see Fig.6 in Ref. 26. In consequence, even though single AuNP of larger diameter exhibits higher absorption efficiency, the collective photothermal effect is partly counteracted by the aforementioned factors.…”

Nanoparticle assisted photothermal deformation of individual neuronal organelles and cells

“…The thermal energy is also transferred to the surrounding media through phonon-phonon interactions and results in the thermal effects observed [8]. The collective effect of exciting the surface plasmon using light and resulting in an increase in temperature of the surrounding media is known as light-to-heat conversion [27].…”

“…Since hemoglobin and water have the highest transmissivity in the NIR [7] this enables the stimulation of nanoparticles deeper into the tissue. When the nanoparticles are illuminated with laser light at a wavelength close to that of the surface plasmon, the electromagnetic energy absorbed heats up the electrons which thermalize with the lattice and the surrounding media [8,9]. This transfer of thermal energy can affect the surrounding tissue in several ways.…”

Analytical Modeling of the Light-to-Heat Conversion by Nanoparticle Ensemble under Radiation Action

“…INTRODUCTION In recent years the absorption of radiation energy by NPs, light-to-heat conversion, heat dissipation and exchange with a surrounding material (medium), and following thermal and accompanied phenomena have become increasingly important topics in nanotechnology . Many reasons exist for this interest, including the applications of the light-to-heat conversion in nanoenergy [1][2][3][4][5][6][7][8][9][10][11][12], in photothermal laser nanomedicine [13][14][15][16] and catalysis [17,18], in laser processing of NPs (laser induced transformation of NP size, shape and structure) [19][20][21][22][23][24], etc. These advances in nanotechnology are based on the efficiency of light-to-heat conversion, thermal effects and the processes induced by the laser-NP interaction [1][2][3][4][5][6][7][8][9][10][11][12].…”

“…Theoretical investigation of the light-to-heat conversion under action of radiation on NPs [1][2][3][4][5][6][7][8][9][10][11][12] is predominantly based on the description of the processes with single NP. The light-to-heat conversion with NP ensemble practically did not investigate and only a few general equations were formulated and the estimations were made.…”