Noble metal nanoparticles due to their unique optical properties arising from their interactions with an incident light have been intensively employed in a broad range of applications. This review ...comprehensively describes fundamentals behind plasmonics, used to develop applications in the fields of biomedical, energy, and information technologies. Basic concepts (electromagnetic interaction and permittivity of metals) are discussed through Mie theory presented as the main model for interpreting phenomena of optical absorption and scattering. The effects of near‐field enhancement, shape, composition, and surrounding medium of nanoparticles on optical properties are described in detail. The review explores and identifies the potential of plasmonic nanoparticles based on their optical properties (e.g., light absorption, scattering, and field enhancement) for developing different applications (biomedical, energy and information technologies). Due to a significant impact of plasmonic nanoparticles on medicine and healthcare products and technologies, the review initially focuses on biomedical applications extensively benefited from optical features of these nanoparticles. Advantages of the optical properties outstandingly implemented are also briefly discussed in other applications, including energy and information technologies. This review concisely summarizes the explored areas based on plasmonic properties, compares advantages of plasmonic nanoparticles over other types of nanomaterials and highlights challenges.
Plasmonic‐metal nanoparticles, on account of their extraordinary optical properties, are widely applied in various fields based on the absorption, scattering, and near field enhancement effects. The fundamental mechanisms and application‐oriented plasmonic properties of plasmonic‐metal nanoparticles are comprehensively discussed and examined to illustrate their potential for developing cutting‐edge biomedical, energy, and information technologies.
Abstract
We present the use of a power limiting apparatus to evaluate ultrafast optical nonlinearities of transparent liquids (water and ethanol) in the femtosecond filamentation regime. The setup ...has been previously employed for the same purpose, however, in a longer pulsewidth (> 20 ps) regime, which leads to an ambiguous evaluation of the critical power for self-focusing. The uncertainty originates from the existence of a threshold power for optical breakdown well below the critical power for self-focusing within this timeframe. Contrarily, using the proposed apparatus in the femtosecond regime, we observe for the first time a unique optical response, which features the underlying physics of laser filamentation. Importantly, we demonstrate a dependence of the optical transmission of the power limiter on its geometrical, imaging characteristics and the conditions under which a distinct demarcation for the critical power for self-focusing can be determined. The result is supported by numerical simulations, which indicate that the features of the observed power-dependent optical response of the power limiting setup are physically related to the spontaneous transformation of the laser pulses into nonlinear conical waves.
The generation of nanobubbles around plasmonic nanostructures is an efficient approach for imaging and therapy, especially in the field of cancer research. We show a novel method using infrared ...femtosecond laser that generates ≈800 nm bubbles around off-resonance gold nanospheres using 200 mJ/cm2 45 fs pulses. We present experimental and theoretical work that demonstrate that the nanobubble formation results from the generation of a nanoscale plasma around the particle due to the enhanced near-field rather than from the heating of the particle. Energy absorbed in the nanoplasma is indeed more than 11 times the energy absorbed in the particle. When compared to the usual approach that uses nanosecond laser to induce the extreme heating of in-resonance nanoparticles to initiate bubble formation, our off-resonance femtosecond technique is shown to bring many advantages, including avoiding the particles fragmentation, working in the optical window of biological material and using the deposited energy more efficiently.
The intention of this paper is to study the physical mechanism underlying the response of gold nanoparticle (AuNP) dimers to a near-infrared off-resonance femtosecond pulse laser in aqueous medium. ...We show that the strongly localized field enhancement in the gap distance and around nanoparticles significantly reduces the laser fluence threshold to achieve an optical breakdown in comparison with an AuNP monomer. This optical breakdown results from highly localized plasma in surrounding media where the nanoparticles stay intact. Also the impact of the gap distance, field polarization, laser fluence and pulse duration on the energy deposition in plasma is presented. These results can be used to make nanoscale plasmonic devices for variety of absorption-based applications.
We present a theoretical and experimental study that reveals the physical mechanism underlying the response of an in-resonance gold nanorod (AuNR) in water to a near-infrared ultrafast laser pulse. ...Results reveal the presence of two different regimes of interaction, depending on the irradiation fluence. For fluences below 3 mJ/cm2, AuNRs are in the so-called absorption regime and are shown to strongly absorb energy, leading to a fast temperature increase revealed by the onset of characteristic mechanical vibration of the structure. In situ measurement demonstrates a permanent deformation of the AuNRs occurring for fluences over 100 μJ/cm2. In the absorption regime, we show the formation of a nanoscale plasma around the structure, dominated by a photothermal emission from the AuNR, and the generation of a pressure wave. However, no cavitation occurs under the deformation threshold fluence (100 μJ/cm2). For fluences over 3 mJ/cm2, in the near-field regime, the energy transfer is dominated by the enhanced near-field around the particle that directly ionizes and heats a nanoplasma in the surrounding water. We theoretically show that bubbles with diameters ≈ 490 nm can be generated in this near-field regime for an incident fluence of 200 mJ/cm2. In situ optical characterization of the produced bubbles supports this result and shows that bubbles with diameters ≈ 200–600 nm can be generated for fluences ranging 100–400 mJ/cm2. Important shielding of the laser–nanostructure interaction by the surrounding plasma is shown to decrease considerably the near-field enhancement, the energy absorption, and the diameter of the generated bubbles and may explain the smaller bubbles generated around in-resonance 10 × 41 nm2 AuNRs when compared to off-resonance 25 × 60 nm2 AuNRs and 100 nm AuNPs.
A femtosecond laser irradiation approach has been developed for the production of homogeneous AuAg nanoalloys of various compositions. The mean size was controlled by the dextran−nanoparticle ...affinity and resulted in the production of 5−7 nm nanoalloys for all nanoparticle compositions. Strong improvement of the oxidation resistance resulted from the increase of the atomic gold fraction in the nanoparticles. At gold fractions above 0.4, most of the nanoparticle oxidation was quenched, inhibiting the release of toxic silver ions in solution. The oxidation of the produced nanoparticles was mainly attributed to the generation of free radicals (O•, H•, •OH) and of molecular reactive oxygen species (O2, H2, H2O2) formed by the decomposition of the water molecules through femtosecond laser-induced optical breakdown. For some biological applications, like surface-enhanced Raman spectroscopy (SERS), it is anticipated that AuAg nanoalloys would be the best compromise in terms of chemical stability and plasmonic response, as they possess much better resistance to oxidation in comparison to pure silver and a much stronger and narrower plasmon peak in comparison to pure gold.
We report on experimental observations of phenomenological self-trapping in plasmonic colloids of varying plasmon peaks in the visible/near infrared. A femtosecond (fs) oscillator is used in both ...pulsed (35 fs, 76 MHz) and continuous wave (cw) operation for comparison. We show that for both modes and for all examined colloids (and under typically applied external focusing conditions in self-trapping studies in colloidal media) nonlinear propagation is governed by thermal defocusing of the focused beam, which precedes the steady-state regime reached by particle diffusion, even far from the plasmon resonance (or equivalently for non-plasmonic colloids, even for low absorption coefficients). A strategy for the utilization of high repetition fs pulses to mitigate thermal lensing and promote gradient force-induced self-trapping is discussed. Notably, nonlinear thermal lensing is further accompanied by natural convection due to the horizontal configuration of the setup. Under resonant illumination, for both fs and cw cases, we observe mode break-up of the beam profile, most likely due to azimuthal modulation instability. Importantly, time-resolved observations of the break-up indicate that in the fs case, thermal convection heat transfer is reduced in magnitude and significantly decoupled in time from thermal conduction, presumably due to temperature increase confinement near the particles. We anticipate that our findings will trigger interest toward the use of high repetition fs pulses for self-channeling applications in nano-colloids.
Abstract A femtosecond laser based transfection method using off-resonance plasmonic gold nanoparticles is described. For human cancer melanoma cells, the treatment leads to a very high perforation ...rate of 70%, transfection efficiency three times higher than for conventional lipofection, and very low toxicity (<1%). Off-resonance laser excitation inhibited the fracture of the nanoparticles into possibly toxic DNA intercalating particles. This efficient and low toxicity method is a promising alternative to viral transfection for skin cancer treatment.
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.
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