Theoretical and experimental investigations on the photo-thermal effect of gold nanorods irradiated by femtosecond and nanosecond laser

Abstract

Nanoparticle-mediated laser-induced breakdown (LIB) can be used for Nanoparticle synthesis, cell nanosurgery and laser-induced breakdown spectroscopy (LIBS). To investigate the photo-thermal conversion of gold nanoparticles during pulsed laser irradiation, the electron-phonon two-temperature model was established in this study. The impact of laser energy density and pulse width on the thermal conversion and morphology change of gold nanorods were investigated and compared with experimental observations. The results show that the melting threshold of gold nanorods under nanosecond laser irradiation is about twenty times that of femtosecond laser irradiation. The mechanisms of nanorod fragmentation are different between fem to and nanosecond laser irradiation: particle melting is more likely to occur in nanosecond laser irradiation, while the Coulomb explosion is highly likely to occur in femtosecond laser irradiation.

Enhancement of the photoacoustic effect during the light–particle interaction

“…37 Under laser irradiation, the heat of nanospheres is transferred to the surrounding medium. In the previous works, based on a TTM, the simulations of thermal problems excited using picosecond and nanosecond pulse lasers have been reported, such as the thermal conversion and morphology change of gold nanorods excited with a 7 ns pulse laser, 38 the thermal diffusion during laser-induced ablation of metals (25 ns), 39 and the energy deposition processes initiated by 30 ps laser excitation, 40 etc. Therefore, when t w lies within the range from 10 ps to 10 ns, the temperature T can be calculated using a TTM: 41…”

“…37 Under laser irradiation, the heat of nanospheres is transferred to the surrounding medium. In the previous works, based on a TTM, the simulations of thermal problems excited using picosecond and nanosecond pulse lasers have been reported, such as the thermal conversion and morphology change of gold nanorods excited with a 7 ns pulse laser, 38 the thermal diffusion during laser-induced ablation of metals (25 ns), 39 and the energy deposition processes initiated by 30 ps laser excitation, 40 etc. Therefore, when t w lies within the range from 10 ps to 10 ns, the temperature T can be calculated using a TTM: 41 where c e , c l and c w are the heat capacity per unit volume of the gold electron, the heat capacity per unit volume of the gold lattice, and the heat capacity per unit mass of water, respectively, κ is the thermal conductivity, g is the electron–lattice coupled coefficient, t is time, ρ is density, and S ( t ) is the heat source density, which can be calculated using the following equation: 21 S ( t ) = C abs · I ( t )/ V p where V p is the volume of gold nanospheres and I is the power density of the Gaussian pulse laser: 21 where F is the laser flux, t 0 is the peak time of the laser power, is the standard deviation of the Gaussian function, and t w is the pulse duration.…”

Nanomedicine: Treatment of Chronic Disease Using Gold Nano Thermo Robot (GNTR) Empowered With Nanotechnology Approaches

“…However, the clinical translation of these agents is continuing, and further study is required to fully understand their safety, effectiveness, and long-term implications in human patients [10].…”

“…In current years, the integration of gold nanoparticles (AuNPs) has emerged as a ground-breaking strategy to enhance the strength of heat in breast cancer treatment. Heat can be rapidly released because of the Coulomb explosion effect [25].…”

“…P = σ abs I, where σ abs as the Gold Nano Robot's cross section of absorption. If σ abs is large enough, a thermal explosion of the Gold Nano Robot may occur at certain values of the threshold laser intensity 𝐸 𝑒𝑥𝑝 ρ which is less than the threshold intensity for optical plasma formation in the surrounding medium [109]. Under the thermal explosion of Gold Nano Robots, The specific situation where the energy required for a complete thermal explosion of the Gold Nano Robots ρ q V = 𝑁 𝐴 u 𝑞 1 V and energy absorbed by the gold nanoparticles of GNTRs during the time of its inertial retention in vapor condition is 𝑒 𝑒𝑥𝑝𝑙 = 𝑅 𝑢 𝑠 , go beyond the energy required for the Gold Nano robot's complete desertion.…”