Extinction Cross Section Research Articles

Analysis of optical properties of diallyldimethylammonium chloride dielectric-coated gold nanospheres for targeted drug delivery

This study theoretically analyzed the optical properties and electric field enhancement of gold nanospheres. Based on numerical analysis, the gold nanospheres were coated experimentally with diallyldimethylammonium chloride (C8H16ClN) for targeted drug delivery. Numerically, a resonance peak for 10 nm nanospheres was observed at 510 nm. As the radius increased from 10 nm to 100 nm, the resonance peak shifted from 510 nm to 605 nm. The nanosphere radius also affected the extinction cross-section. The resonance peaks showed a red shift as the radius of the nanosphere increased. For experiment analysis, gold nanospheres were synthesized using a seed-mediated technique and then coated with different concentrations of C8H16ClN. The UV absorbance by the nanospheres increased with an increase in the concentration of C8H16ClN from 10 mg ml−1 to 20 mg ml–1. UV–vis spectrum confirmed a rise in resonance peaks with increasing coating concentration. The coated gold nanospheres were used to deliver the doxorubicin-HCl (DOX-HCl) drug. Maximum drug release was observed when the temperature was set at 50 °C. It was concluded that the nanospheres, coated with 20 mg ml–1 of C8H16ClN, are excellent candidates for drug delivery applications. The gold nanospheres with a radius of 50 nm were best for target drug delivery, and the particles above 50 nm were best for thermal therapies for cancer treatment.

Electrodynamic single-particle trap integrated into double-cavity ring-down spectroscopy for light extinction

The study of the interaction of light with matter upon changing environmental conditions requires new platforms that provide accurate and reliable measurements. One suitable technique for studying such interaction uses electrodynamic traps to levitate micro or nanoparticles in combination with an optical interrogation technique, but improvements and new developments that complement spectroscopic information are necessary. Here, we use a Paul Electrodynamic Trap (PET) coupled to a Double-Cavity Ring Down Spectroscopy (D-CRDS) to measure the extinction cross section of single levitated particles at two different wavelengths (405 and 532 nm). The level of control achieved over the motion and stability is such that the particle can be consecutively placed at the central maximum of two independent TEM00 Gaussian modes of the ring-down cavities. Therefore, we can directly measure the dynamic change of the extinction cross section of a single particle at two different wavelengths. The combination of simulations using Mie theory and experiments demonstrates the potential of this robust and versatile setup applied to 1,2,6-hexanetriol particles. Unlike standard methods, our system provides crucial information of drastic and reversible change in the extinction cross-section of a sodium chloride particle in efflorescence and deliquescence points, indicating changes in solute mass, charge, refractive index, sphericity and size during the dehydration and hydration processes.

Localize surface plasmon resonance of silver nanoparticles using Mie theory

In this work, the optical properties of silver nanoparticles (AgNPs) were explored using Mie theory compared with the experimental AgNPs using the chemical reduction method. Mie’s theory is suited for accurately evaluating the scattering, absorption, and extinction cross-sections of spherical AgNPs. Therefore, the wavelength of localized surface plasmon resonance (LSPR) in the optical spectra of the spherical AgNPs was calculated. The experimental AgNPs have a spherical shape with an average particle size of 30 nm. In addition, the crystalline structure of AgNPs was found to be cubic with fcc structure with lattice constant a= 4.155 Å. Moreover, the excitation of the LSPR of the AgNPs was simulated using the finite-difference time-domain (FDTD) method at different wavelengths to explore the LSPR phenomena. The results show that spherical AgNPs are the most widely used materials in biosensors, biomedicine, optoelectronic devices, and solar cells due to their surface plasmon resonances in the visible spectrum region.

Multi-frequency and wide-angle nonreciprocity arising from non-uniform magnetic field

We investigate the effect of non-uniform external static magnetic field on the scattering nonreciprocity of a deep-subwavelength gyrotropic particle system. Based on a scattering matrix approach, we show analytically that asymmetrical extinction cross section of the scattering system for opposite illumination directions can be accessed at multi-frequency and wide-angle regimes, in the presence of magnetic field with weak spatial non-uniformity. A simplified dual-dipole model is further employed to capture the generic physics of nonreciprocal scattering, essentially attributed to the asymmetrical magneto-electric cross interactions. In addition, typical examples are provided with full-wave numerical verifications. Our finding may open a straightforward and efficient pathway to manipulate nonreciprocal scattering at the subwavelength scale.

Failures of the classical optical theorem under arbitrary-shaped beam incidence in electromagnetism, acoustics, and quantum mechanics: motivation and a review

The classical optical theorem states that for a wave propagating in a lossless medium and incident on a finite scatterer, the extinction cross section is proportional to the real part of the scattering amplitude in the forward direction. When developing a light scattering theory known as the generalized Lorenz–Mie theory, it has been a surprise to observe that in 1982, the optical theorem failed when the scatterer was illuminated by an arbitrary-shaped beam. The extremely simple reason for that failure has been understood only in 2014 and published in 2016. This represents a more than three-decade-long story, which is called a “wow” story for reasons that will be mentioned in this paper. The opportunity of this story which pertains to both the history and philosophy of sciences is considered to provide a review of the optical theorem under arbitrary-shaped beam incidence in electromagnetism, acoustics, and quantum mechanics.

Modelling of nanosensors based on localised surface plasmon resonance

ABSTRACT To design nanosensors based on localised surface plasmon (LSP), a structure is considered consisting of metal nanoparticles and study the influence of nanoparticles size, material, geometry, and background refractive index (RI) on its performance. We propose a nanosensor based on nanoplasmonic and investigate its sensitivity. The boundary element method is employed to calculate the extinction cross-section and sensitivity of the proposed sensor. We study the effect of various parameters on LSP resonance. Our calculations about extinction, scattering, and absorption spectra have been compared with experimental data. According to the comparison, it is deduced the boundary element method provides acceptable results. It is shown that the proposed nanosensor is very sensitive to the variation of sample RI. Moreover, it is possible to adjust the required spectral range by changing the geometry and material of nanoparticles. Here, the highest sensitivity is obtained for cubic nanoparticles made of silver.

Extinction and attenuation by voids in absorbing host media.

Extinction and attenuation by particles in an absorbing host have suffered a long-lasting controversy, which has impeded the physical insights on the radiative transfer in the voids dispersed composite. In this paper, we outline the existing extinction definitions, including an equivalence theorem neglecting the host absorption, the near-field analytical definition neglecting the far-field effects, and the operational way which simulates the actual detector readings. It is shown that, under the independent scattering approximation, the generalized operational definition is equivalent to a recent effective medium method according to the rigorous theory of multiple scattering. Using this generalized extinction, we show the important influences of the host absorption on the void extinction. Specifically, at the void resonance, the extinction cross sections of the small voids can be positive, zero, and even negative, which is regulated quantitively by host absorption. Considering the voids in SiC or Ag, the intriguing properties are verified through the attenuation coefficient calculated by the Maxwell-Garnett effective medium theory. In contrast, the equivalent theorem cannot describe any void resonance structures in the absorbing media. Also, the near-field definition fails to generate negative extinction and cannot thus describe the diminished total absorption by the voids. Our results might provide a better understanding of complex scattering theory in absorbing media.

An overview of the optical characterization of free microparticles and their radiative properties

We discuss how the range of information available from microparticle analysis can be extended in a number of applications by measuring a specific set of optical properties of individual particles using light scattering. Central to these measurements are the real and imaginary components of the forward scattered field, the former being equal to the extinction cross-section except for a few particle-independent constants. Although still a niche technique, it has some inherent advantages and great potential for particle characterization, especially in the challenging near-wavelength size range. A selection of cases is covered from an experimental point of view, while some essential models are introduced to illustrate the underlying physical phenomena. We present a benchmark of experimental results from the literature and other examples that support optical diagnostics applied in science and industrial processes. As a key point of this work, we show that by accessing the fundamental properties of scatterers the inversion of light scattering data can be avoided. This provides model-independent results closer to application requirements without the drawbacks of case-specific assumptions.

Nonlocal Hydrodynamic Model with Viscosive Damping and Generalized Drude–Lorentz Term

The response of plasmonic metal particles to an electromagnetic wave produces significant features at the nanoscale level. Different properties of the internal composition of a metal, such as its ionic background and the free electron gas, begin to manifest more prominently. As the dimensions of the nanostructures decrease, the classical local theory gradually becomes inadequate. Therefore, Maxwell’s equations need to be supplemented with a relationship determining the dynamics of current density which is the essence of nonlocal plasmonic models. In this field of physics, the standard (linearized) hydrodynamic model (HDM) has been widely adopted with great success, serving as the basis for a variety of simulation methods. However, ongoing efforts are also being made to expand and refine it. Recently, the GNOR (general nonlocal optical response) modification of the HDM has been used, with the intention of incorporating the influence of electron gas diffusion. Clearly, from the classical description of fluid dynamics, a close relationship between viscosive damping and diffusion arises. This offers a relevant motivation for introducing the GNOR modification in an alternative manner. The standard HDM and its existing GNOR modification also do not include the influence of interband electron transitions in the conduction band and other phenomena that are part of many refining modifications of the Drude–Lorentz and other models of metal permittivity. In this article, we present a modified version of GNOR-HDM that incorporates the viscosive damping of the electron gas and a generalized Drude–Lorentz term. In the selected simulations, we also introduce Landau damping, which corrects the magnitude of the standard damping constant of the electron gas based on the size of the nanoparticle. We have chosen a spherical particle as a suitable object for testing and comparing HD models and their modifications because it allows the calculation of precise analytical solutions for the interactions and, simultaneously, it is a relatively easily fabricated nanostructure in practice. Our contribution also includes our own analytical method for solving the HDM interaction of a plane wave with a spherical particle. This method forms the core of calculations of the characteristic quantities, such as the extinction cross-sections and the corresponding components of electric fields and current densities.

Spitzer IRS Observations of Titan as a Precursor to JWST MIRI Observations

In this work, we present for the first time infrared spectra of Titan from the Spitzer Space Telescope (2004–2009). The data are from both the short wavelength–low resolution (SL; 5.13–14.29 μm, R ∼ 60–127) and short wavelength–high resolution (SH; 9.89–19.51 μm, R ∼ 600) channels showing the emissions of CH4, C2H2, C2H4, C2H6, C3H4, C3H6, C3H8, C4H2, HCN, HC3N, and CO2. We compare the results obtained for Titan from Spitzer to those of the Cassini Composite Infrared Spectrometer (CIRS) for the same time period, focusing on the 16.35–19.35 μm wavelength range observed by the SH channel but impacted by higher noise levels in the CIRS observations. We use the SH data to provide estimated haze extinction cross sections for the 16.67–17.54 μm range that are missing in previous studies. We conclude by identifying spectral features in the 16.35–19.35 μm wavelength range that could be analyzed further through upcoming James Webb Space Telescope Cycle 1 observations with the Mid-Infrared Instrument (5.0–28.3 μm, R ∼ 1500–3500). We also highlight gaps in the current spectroscopic knowledge of molecular bands, including candidate trace species such as C60 and detected trace species such as C3H6, that could be addressed by theoretical and laboratory study.

Nano-shaping of chiral photons

Abstract Localized surface plasmon polaritons can confine the optical field to a single-nanometer-scale area, strongly enhancing the interaction between photons and molecules. Theoretically, the ultimate enhancement might be achieved by reducing the “photon size” to the molecular extinction cross-section. In addition, desired control of electronic transitions in molecules can be realized if the “photon shape” can be manipulated on a single-nanometer scale. By matching the photon shape with that of the molecular electron wavefunction, optically forbidden transitions can be induced efficiently and selectively, enabling various unconventional photoreactions. Here, we demonstrate the possibility of forming single-nanometer-scale, highly intense fields of optical vortices using designed plasmonic nanostructures. The orbital and spin angular momenta provided by a Laguerre–Gaussian beam are selectively transferred to the localized plasmons of a metal multimer structure and then confined into a nanogap. This plasmonic nano-vortex field is expected to fit the molecular electron orbital shape and spin with the corresponding angular momenta.

Study of enhanced sensitivity of nanosensors by using gold bowtie nanoparticles

A plasmonic nanosensor is proposed and investigated its sensitivity using the optical properties of plasmonic nanoparticles. To this end, we first consider the nanosensor consisting of bowtie nanoparticles. Then, the nanosensor performance is examined under different factors such as the refractive index of the background environment, the height, and length of the nanoparticles. The proposed bowtie nanoparticles, in this work, are made of gold. The boundary element method is used to simulate the nanosensor. The extinction cross-section is computed in terms of wavelength and the effect of various factors on the resonance wavelength of localized surface plasmon is investigated. It is shown that the nanosensor investigated in this research has a high sensitivity to the changes in the refractive index of the studied sample. The sensitivity of the nanosensor is obtained as 650[Formula: see text]nm/RIIU. In addition, the required spectral range can be arbitrarily adjusted by the type of nanoparticles.

Paradigmatic examples for testing models of optical light polarization by spheroidal dust

We present a general framework on how the polarization of radiation due to scattering, dichroic extinction, and birefringence of aligned spheroidal dust grains can be implemented and tested in 3D Monte Carlo radiative transfer (MCRT) codes. We derive a methodology for solving the radiative transfer equation governing the changes of the Stokes parameters in dust-enshrouded objects. We utilize the Müller matrix and the extinction, scattering, linear, and circular polarization cross sections of spheroidal grains as well as electrons. An established MCRT code is used, and its capabilities are extended to include the Stokes formalism. We compute changes in the polarization state of the light by scattering, dichroic extinction, and birefringence on spheroidal grains. The dependency of the optical depth and the albedo on the polarization is treated. The implementation of scattering by spheroidal grains both for random walk steps as well as for directed scattering (peel-off) are described. The observable polarization of radiation of the objects is determined through an angle binning method for photon packages that leaves the model space as well as through an inverse ray-tracing routine for the generation of images. We present paradigmatic examples for which we derive analytical solutions of the optical light polarization by spheroidal dust particles. These tests are suited for benchmark verification of MCPOLand other such codes and allow the numerical precision reached by these codes to be quantified. We demonstrate that MCPOLis in excellent agreement (within ~0.1%) of the Stokes parameters when compared to the analytical solutions.

Aggregation of magnetic nanoparticles functionalized with trans-resveratrol in aqueous solution

In the framework of a protein–ligand-fishing strategy to identify proteins that bind to trans-resveratrol, a natural phenolic compound with pharmacological benefits, we have developed magnetic nanoparticles covalently linked to trans-resveratrol through three different derivatives and examined their aggregation behavior in aqueous solution. The monodispersed magnetic core (18 nm diameter) with its mesoporous silica shell (93 nm diameter) exhibited a notable superparamagnetic behavior useful for magnetic bioseparation. The hydrodynamic diameter, deduced from dynamic light scattering analysis, of the nanoparticle increased from 100 to 800 nm when the aqueous buffer changed from pH 10.0–3.0. A size polydispersion occurred from pH 7.0–3.0. In parallel, the value of the extinction cross section increased according to a negative power law of the UV wavelength. This was mainly due to light scattering by mesoporous silica, whereas the absorbance cross section remained very low in the 230–400 nm domain. The three types of resveratrol-grafted magnetic nanoparticles exhibited similar scattering properties, but their absorbance spectrum was consistent with the presence of trans-resveratrol. Their functionalization increased their negative zeta potential when pH increased from 3.0 to 10.0. The mesoporous nanoparticles were monodispersed in alkaline conditions, where their anionic surface strongly repulsed each other but aggregated progressively under van der Waals forces and hydrogen bonding when negative zeta potential decreased. The characterized results of nanoparticle behavior in aqueous solution provide critical insight for further study of nanoparticles with proteins in biological environment.

Impactor collection efficiencies can modify the uncertainty of multiply charged particles in optical extinction measurements

The complex distribution of particle charge states resulting from neutralization processes by radioactive or soft X-ray charge neutralizers is a well-documented problem in aerosol science. Here, we demonstrate that non-idealities in the collection efficiency of an impactor allows for the transmission of an unexpected population of multiply charged particles by a differential mobility analyzer that can bias optical measurements. The extinction cross sections (Cext) of ammonium sulfate particles were quantified using cavity ring-down spectroscopy and particle counting. Particles were selected by electrical mobility (i.e., a metric of particle size) using a differential mobility analyzer (DMA) or electrical mobility and mass selected by a tandem DMA and aerosol particle mass analyzer (APM), respectively, to elucidate multiple charging artifacts. Measured Cext exhibited statistically significant differences at particle sizes near the impactor cut point implying that these multiply charged particles should not be present and could not be confirmed by parallel size distribution measurements. Additionally, comparison of Cext with Mie theory demonstrates that misclassification of the multiply charged particles can give rise to numerically accurate results. To understand these observations, the collection efficiency (CE) of four impactors from similar electrostatic classifiers was investigated. From these measurements, it was determined that the nominal and actual diameters of the impactors differed by −0.5% (457 μm vs. (455 ± 1) μm, respectively (uncertainty is 1σ standard deviation)) but the average Stk50 (the Stokes number at the cut-point, D50) values differed by ≈ 23% (0.23 vs. 0.18 ± 0.01, respectively). The measured CE as a function of √Stk (a metric of particle aerodynamic size) exhibits a long tail toward higher √Stk values, allowing for transmission of the larger and multiply charged particles observed in the optical measurements. These measurements highlight the utility of using orthogonal, spectroscopic methods to quantify the presence of multiply charged particles.

The non-linear evolution of radiative properties of plasmonic nanofluid during light-induced vaporization process

The light-induced vaporization process of plasmonic nanofluid plays an essential role in solar energy harvesting. Under light illumination, metallic nanoparticles can be converted into ideal thermal sources at nanoscale and generate plasmonic nanobubbles (PNBs) at the localized surface plasmon resonance (LSPR) wavelength, Therefore, the radiative properties of nanofluid closely correlate with the evolution of PNB nucleation, growth, fusion, and dissipation. A model based on finite element modeling is developed to investigate the evolution of radiative properties. The effect of gold nanoparticle (AuNP) size, PNB size, and AuNP aggregation morphology on the extinction cross section, albedo, and LSPR peak wavelength of particle-bubble complexes (P-B complexes) during the evolution of PNB is determined. The results indicate that with the vaporization process of nanofluid, the evolution of PNBs makes the radiation properties exhibit an obvious non-linear evolution pattern. Specifically, the generation of PNB shifts the LSPR peak wavelength towards blue, while the aggregation of AuNPs shifts it towards red. In the presence of PNB, the variation of the LSPR peak wavelength depends on the competition between the blue-shifting effect of PNB growth and the red-shifting effect of AuNP aggregation. After PNB dissipation, the aggregation of AuNPs raises the aggregates’ albedo. An albedo lower than 0.5 indicates a strong absorption of incident light energy. The increase in AuNP size, PNB size, and the aggregation of AuNPs all contribute to the increase in the peak extinction cross section. When PNB is present, whether the albedo of P-B complexes exceeds 0.5 depends on the relative magnitude of the extinction cross section of AuNP aggregates and PNB. The increase in the number of AuNPs aggregation layers causes the blue-shifted LSPR peak wavelength of AuNP aggregates, the decreased peak extinction cross section, the increased LSPR peak width, and the potential for multiple extinction peaks.

Evaluating the accuracy of absorbing aerosol optical properties measured using single particle cavity ring-down spectroscopy

Single particle cavity ring-down spectroscopy (CRDS) allows direct and continuous measurements of the extinction cross-sections for levitated micron-scale aerosol particles of constant or evolving composition. Our recent interests have concerned single particle CRDS measurements for light-absorbing particles. These measurements are made on single, spherical particles evaporating over the radius range 1500–700 nm that are levitated within a 405-nm cavity ring-down spectrometer using a linear electrodynamic quadrupole trap. Here, we quantify the accuracy and precision of our cavity ring-down time measurements and the consequences of particle motion within our electrodynamic trap. Next, we estimate the uncertainty in our particle size retrievals from angularly resolved elastic light scattering measurements for particles with a range of absorption strengths. Finally, we assess the accuracy of complex refractive index values retrieved from simultaneous ring-down time and particle size measurements. The assessments account for the impacts of shot and detector noise in the measured ring-down times, the driven particle motion within the electrodynamic trap, and particle absorption strength (for imaginary refractive indices in the range ∼0.0–0.1). The real and imaginary refractive indices are retrieved to an accuracy better than 0.005 and 0.002, respectively, for almost all absorption strengths studied, and for particles of constant or evolving composition. Although particles confined in our electrodynamic quadrupole trap undergo considerable levels of driven motion (with oscillation amplitudes of several tens of micrometers), the contribution of this motion to uncertainty in retrieved refractive indices is negligible compared to contributions from particle sizing errors.

Thermal radiative properties of polyamide-12 from 0.2 to 1.1 μm

Microplastics are an emerging marine pollutant, and their negative impacts on the photosynthetic efficiency of marine photoautotrophs are gradually endangering marine ecosystems and biota. To analyze and solve the impact of microplastic particles on light propagation in the ocean, the investigation of radiative properties of microplastic particles is essential. The extinction and absorption coefficients of polyamide-12 (PA12) with different particle concentrations are experimentally measured using transmission and integration methods in the spectral range of 200 to 1100 nm. The extinction and absorption cross sections are obtained from the measured extinction and absorption coefficients. The measured PA12 absorption peaks, located at 692, 728, 764, 835, and 940 nm, correspond to the vibrational absorption of methylene groups (-CH2) and amide groups (CO-NH). The scattering albedo of PA12 is mostly above 0.7 in the visible spectral, indicating that PA12 is a scattering dominated medium. The measured radiative properties of PA12 provide optical parameters for determining the radiative transfer containing microplastics.

Effects of shape on the optical properties of CdSe@Au core-shell nanocomposites

We studied the local field enhancement factor (LFEF), absorption, and extinction cross sections of spherical, cylindrical, oblate, and prolate core–shell nanocomposites (NCs) theoretically and numerically using the quasi-static approach. By solving Laplace’s equations, we obtained expressions for the LFEF, polarizability, absorption, and scattering cross sections for each of the core–shell NCs. We found that the LFEF, absorption, and extinction cross section of spherical and cylindrical core–shell NCs possess two peaks whereas oblate and prolate spheroids show three observable peaks. Moreover, the prolate core–shell spheroid shows greater tunability and larger intensity of the LFEF than its corresponding oblate structure. Furthermore, spherical nanoshells are characterized by the higher LFEF than cylindrical and spheroidal core–shells of the same size and composition. When compared, even the smallest value of the LFEF of the spherical core–shell is 11.42 and 10.09 times larger than the biggest values of oblate and prolate core-shells, respectively. The study also indicated that for spherical and cylindrical NCs, the first two peaks of the LFEF and extinction cross sections are achieved at the same corresponding frequencies. Furthermore, all peaks of the extinction cross sections of the prolate spheroid are found to be the lowest while those of the cylindrical peaks are the highest. Where there are an equal number of peaks of different shapes, the peak values are different, showing that shapes of core–shell NCs determine the intensity, the number, and the positions of peaks of the LFEF and optical cross sections. Such NCs are promising for applications in optical sensing, bio-sensing, and electronic devices. Especially, gold coated core–shell spheroids have good potential applications in multi-channel sensing.

Optimizing Color of Particulate Products

AbstractOptical properties of nanoparticles largely depend on their shape and material distribution. Given any such property, e.g., a desired color, the aim is to design an optimal nanoparticle, whose properties best match these targets. The corresponding nonlinear optimization problem is challenging due to numerous difficulties: The objective function is given by a multi‐dimensional integral over wavelengths, directions of incoming light rays and nanoparticle design distributions, where the integrand depends on the extinction cross section of the nanoparticle design.Thus, classical full gradient schemes based on numerical integration prove ineffective due to their tremendous computational cost. On the other hand, known stochastic gradient descent methods cannot deal with the nonlinear fashion in which the design variables enter the objective function. Therefore, we introduce the continuous stochastic gradient (CSG) method, which does not compute a full gradient, but instead uses information from previous iterations in an optimal way to learn the exact gradient during the optimization process. Hence, CSG thematically lies in between a stochastic optimization scheme and a full gradient method, combining both the low computational cost of SG due to very few partial gradient evaluations (small “batch size”) as well as step size rules and line search techniques known from full gradient descent.