Prediction of photothermal phase signatures from arbitrary plasmonic nanoparticles and experimental verification

Abstract

We present a new approach for predicting spatial phase signals originating from photothermally excited metallic nanoparticles of arbitrary shapes and sizes. The heat emitted from such a nanoparticle affects the measured optical phase signal via changes in both the refractive index and thickness of the nanoparticle surroundings. Because these particles can be bio-functionalized to bind certain biological cell components, they can be used for biomedical imaging with molecular specificity, as new nanoscopy labels, and for photothermal therapy. Predicting the ideal nanoparticle parameters requires a model that computes the thermal and phase distributions around the particle, thereby enabling more efficient phase imaging of plasmonic nanoparticles and avoiding trial-and-error experiments while using unsuitable nanoparticles. The proposed nonlinear model is the first to enable the prediction of phase signatures from nanoparticles with arbitrary parameters. The model is based on a finite-volume method for geometry discretization and an implicit backward Euler method for solving the transient inhomogeneous heat equation, followed by calculation of the accumulative phase signal. To validate the model, we compared its results with experimental results obtained for gold nanorods of various concentrations, which we acquired using a custom-built wide-field interferometric phase microscopy system. INTRODUCTIONPlasmonic nanoparticles are used in a variety of scientific disciplines because of their unique interactions with electromagnetic fields. Plasmonic nanoparticles are used in photonics to sense or induce changes in certain environments, thereby acting as either nanosensors or nanosources for changes in chemical, thermal, or material properties 1 . In biomedical applications, plasmonic nanoparticles can be used as labels in cells and tissues and are imaged via various effects, including photothermal (PT) imaging, photoacoustic shock-wave imaging, scattering, and polarization imaging 225 . The electromagnetic energy absorbed by a metallic nanoparticle is rapidly transformed into heat through electron-phonon relaxation; thus, nanoparticles in solution act as nanosources of heat, which can be manipulated for imaging or for destructive purposes.Several numerical models of nanoparticles have been proposed to estimate the transfer of heat from a nanoparticle submerged in a liquid to its surroundings 5-8 . These models can yield information on the processes the nanoparticles undergo on time scales or at resolutions smaller than those at which they can be measured. In addition, these models can predict the thermal distribution in the nanoparticle surroundings; thereby making it possible to explain phenomena observed when heated particles interact with other materials, particularly with biological materials that are prone to thermal damage.

Nonlinear plasmonics at high temperatures

“…The TIP approach is appropriate as long as the relative change of of the permittivity, ∆ǫ m ∼ ∆T dǫ m /dT , is small. Typically, the thermo-derivative, dǫ m /dT , varies between ∼ 10 −5 / • K for standard dielectric materials [58] up to 10 −4 − 10 −3 / • K for water [59] or metals [60,61]. Thus, as long as the temperature increase (with respect to room temperature) is modest, i.e., limited to a few degrees, the change of the permittivity is indeed negligible.…”

Enhanced electron extraction capability of polymer solar cells via modifying the cathode buffer layer with inorganic quantum dots

“…[30][31][32][33] It is also an available tool to observe bulk and interfacial electrical properties that cannot be directly observed, 34 such as the built-in voltage, doping concentration, diffusion time, and carrier mobility. [35][36][37][38][39] By modelling the impedance behavior to investigate the charge transport recombination mechanisms, it was found that there is efficient charge transfer between TiO 2 and the active layer, leading to improved electron mobility and energy level alignment for PSCs.…”

Interaction of Pulses of Different Duration with Chemically Prepared Silver Nanoparticles: Analysis of Optical Nonlinearities

“…Metal nanoparticles (NPs) have unique properties allowing applications in mechanics, catalysis, magnetism, optics, electricity, new material development, and heat physics, due to their morphology and size effects [1][2][3][4][5]. Among them, noble metal NPs have potential applications in the field of nanophotonics due to their strong nonlinear optical response, thus attracting significant attention [4][5][6][7][8]. As a typical representative of noble metals, silver nanoparticles (Ag NPs) are particularly prominent [9][10][11][12][13][14][15][16].…”