In this paper, we perform a finite element (FE)-based numerical analysis to calculate the photoacoustic (PA) signal generated by spherical gold-silver (Au-Ag) alloy nanoparticles (NPs). These spherical particles are size-controlled and monodispersed, with tunable plasmonic resonance wavelength via change of the alloy composition. This enables their use in photoacoustic imaging as a contrast agent. This theoretical framework self consistently solves the electromagnetic, thermodynamic and transient acoustic pressure physics using a multiphysics coupling approach. We model our system as an optically heterogeneous medium irradiated by a nanosecond laser pulse in the tissue therapeutic optical window (NIR irradiation, with wavelength of 800 nm). We calculate the photoacoustic signal generated by the photo-thermal expansion of both the particle and its surrounding medium. The results show the impact of the gold molar fraction (GMF) of Au-Ag alloy NPs on the PA signal for different NP sizes. We show that significantly stronger PA signals are achieved using Au-Ag alloy NPs (GMF = 0.55) in comparison with pure AuNPs (GMF = 1) and pure AgNPs (GMF = 0) of the same size and shape.
Nanoscale bubbles generated around laser-excited metallic nanoparticles are promising candidates for targeted drug and gene delivery in living cells. The development of new nanomaterials for efficient nanobubble-based therapy is however limited by the lack of reliable computational approaches for the prediction of their size and dynamics, due to the wide range of time and space scales involved. In this work, we present a multiscale modeling framework that segregates the various channels of plasmon de-excitation and energy transfer to describe the generation and dynamics of plasmonic nanobubbles. Detailed comparison with time-resolved shadowgraph imaging and spectroscopy data demonstrates that the bubble size, dynamics, and formation threshold can be quantitatively predicted for various types of nanostructures and irradiation parameters, with an error smaller than the experimental uncertainty. Our model in addition provides crucial physical insights into non-linear interactions in the near-field that should guide the experimental design of nanoplasmonic materials for nanobubble-based applications in nanomedicine.
Ultrashort pulsed lasers can provide high peak intensity with low pulse fluence. This makes them an ideal choice in photothermal therapy and applications where damage to the surrounding material needs to be minimized. Depending on the peak intensity, the ultrashort pulsed laser’s interaction with matter can lead to plasma formation through nonlinear effects such as multiphoton and impact electron excitation. The capability of the spherical gold nanoparticles, as the most employed nanoparticle so far for photothermal therapy, to enhance and strongly localize the incident laser field leads to plasma formation around the particles at even lower pulse fluences. Under certain circumstances, during the pulse duration, this plasma can absorb more energy than the nanoparticle itself. Consequently, the absorbed energy by the generated plasma can act as an energy source for different phenomena such as the evolution of the temperature distribution, thermoelastic stress generation, and stress-induced bubble formation. In this paper, we study the plasma-mediated interaction of a 45 fs pulsed laser with two types of spherical gold nanoparticles in water: solid nanoparticle and core–shell (silica–gold) nanoparticle. We use a numerical framework based on the finite element method (FEM) to compare energy deposition profiles in these nanoparticles and in their surrounding plasma, by focusing on the impact of the nanoparticle size and the laser fluence. Our calculations show that the maximum energy deposition in plasma occurs in core–shell nanoparticles with a diameter of 130 nm and the ratio of core to shell radius of 0.8 and in solid nanoparticles with a diameter of 170 nm.
Precise spatial and temporal control of pressure stimulation at the nanometer scale is essential for the fabrication and manipulation of nano-objects, and for exploring single-molecule behaviour of matter under extreme conditions. However, state-of-the-art nano-mechanical transducers require sophisticated driving hardware and are currently limited to moderate pressure regimes. Here we report a gold plasmonic bowtie (AuBT) nano-antennas array that can generate extreme pressure stimulus of ∼100 GPa in the ps (10 s) time scale with sub-wavelength resolution upon irradiation with ultra-short laser pulses. Our method leverages the non-linear interaction of photons with water molecules to excite a nano-plasma in the plasmon-enhanced near-field and induce extreme thermodynamic states. The proposed method utilizes laser pulses, which in contrast to micro- and nano-mechanical actuators offers simplicity and versatility. We present time-resolved shadowgraphic imaging, electron microscopy and simulation data that suggest that our platform can efficiently create cavitation nano-bubbles and generate intense pressure in specific patterns, which can be controlled by the selective excitation of plasmon modes of distinct polarizations. This novel platform should enable probing non-invasively the mechanical response of cells and single-molecules at time and pressure regimes that are currently difficult to reach with other methods.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.