Study of Broadband Tunable Properties of Surface Plasmon Resonances of Noble Metal Nanoparticles Using Mie Scattering Theory: Plasmonic Perovskite Interaction

We suggest semi-analytical approach to study the optical properties of noble metal nanoparticles and their interaction to the perovskite material (methyl ammonia lead halide: CH₃NH₃PbI₃). Metal nanoparticles embedded in perovskite matrix exhibits broadband surface plasmon resonances, and the tunability of these plasmonic resonances is highly sensitive to particle size. The calculation of optical cross section have been done using Mie scattering theory which is applicable to arbitrary size and spherical-shape metal nanoparticles. We have taken five different radii ranging from 15 to 100 nm to understand the plasmonic resonances and its spectral width in the wavelength range 300 to 800 nm. Out of these noble metal nanoparticles, silver have highest scattering efficiency nearly of the order of 18 for the case of 15 nm radii at resonance wavelength 613 nm. Our finding reveals a new concept to understand the applications of plasmonic resonances in order to enhance the photon absorption inside the thin film of perovskite.     

Measurements of multiply scattered light for on-line monitoring of changes in size distribution of cell debris suspension

Dual wavelength frequency-domain measurements of photon migration (FDPM) are conducted on filtrate samples obtained from an industrial centrifugation process designed to separate Escherichia coli cell debris from the inclusion bodies. FDPM measurements consist of detecting phase delay of intensity-modulated light at 670 and 820 (or 830) nm. Optical properties of isotropic scattering and absorption are obtained from the regression of phase delay data to the optical diffusion equation. We show that the corresponding intensity-based measurements alone cannot provide accurate and independent estimates for these optical properties. However, FDPM-derived scattering coefficients of filtrate solutions (primarily consisting of 0.1-0.2 micrometer E. coli cell debris) are sensitive to approximately 1 vol % of added inclusion bodies (of 1-2 micrometer size). The technique, theory, and future adaptation of FDPM as an on-line monitor to detect the loss of inclusion bodies in centrifugation following homogenization are presented and contrasted to conventional, intensity-based measurements.     

Tunable Omnidirectional Broadband Band-Stop Filter in Symmetric Hybrid Plasmonic Structures

We numerically investigate a symmetric hybrid waveguide-plasmon system composed of a periodic metallic nanowires pairs array embedded in symmetric dielectric sandwich layers for band-stop filtering in the optical frequency range. The proposed symmetric system shows an omnidirectional broadband absorption enhancement with flat band-stop transmission induced by the coupling and hybridization of photonic and plasmonic modes. The transmission stop band bandwidth ranging from 80 to 585 nm is observed. The bandwidth of the proposed system can be further manipulated by tailoring their geometrics for potential applications in plasmonic-assisted broadband optical filtering.     

405 nm-Excited Fluorescence Spectra of the Juice of the Lemon (Citrus x Limon)

A 405 nm diode laser is used to excite fluorescence of juices of raw and ripe lemons. Emission bands appear approximately at 520 nm and 670 nm. Fluorescence intensity ratio F520/F670 is determined for the two stages. Variation in the fluorescence intensity ratio is observed during the process of ripening or growth of the fruit. Time-resolved spectra at this excitation wavelength reveal two decay times at both the stages at the emission wavelength of 520 nm, and two decay times at the raw stage and one decay time at the ripe stage at 670 nm.     

Investigation of the source‐detector separation in near infrared spectroscopy for healthy and clinical applications

Understanding near infrared light propagation in tissue is vital for designing next generation optical brain imaging devices. Monte Carlo (MC) simulations provide a controlled mechanism to characterize and evaluate contributions of diverse near infrared spectroscopy (NIRS) sensor configurations and parameters. In this study, we developed a multilayer adult digital head model under both healthy and clinical settings and assessed light‐tissue interaction through MC simulations in terms of partial differential pathlength, mean total optical pathlength, diffuse reflectance, detector light intensity and spatial sensitivity profile of optical measurements. The model incorporated four layers: scalp, skull, cerebrospinal‐fluid and cerebral cortex with and without a customizable lesion for modeling hematoma of different sizes and depths. The effect of source‐detector separation (SDS) on optical measurements' sensitivity to brain tissue was investigated. Results from 1330 separate simulations [(4 lesion volumes × 4 lesion depths for clinical +3 healthy settings) × 7 SDS × 10 simulation = 1330)] each with 100 million photons indicated that selection of SDS is critical to acquire optimal measurements from the brain and recommended SDS to be 25 to 35 mm depending on the wavelengths to obtain optical monitoring of the adult brain function. The findings here can guide the design of future NIRS probes for functional neuroimaging and clinical diagnostic systems.      

Light Absorption and Recycling in Hybrid Metal Halide Perovskite Photovoltaic Devices

The production of highly efficient single‐ and multijunction metal halide perovskite (MHP) solar cells requires careful optimization of the optical and electrical properties of these devices. Here, precise control of CH₃NH₃PbI₃ perovskite layers is demonstrated in solar cell devices through the use of dual source coevaporation. Light absorption and device performance are tracked for incorporated MHP films ranging from ≈67 nm to ≈1.4 µm thickness and transfer‐matrix optical modeling is utilized to quantify optical losses that arise from interference effects. Based on these results, a device with 19.2% steady‐state power conversion efficiency is achieved through incorporation of a perovskite film with near‐optimum predicted thickness (≈709 nm). Significantly, a clear signature of photon reabsorption is observed in perovskite films that have the same thickness (≈709 nm) as in the optimized device. Despite the positive effect of photon recycling associated with photon reabsorption, devices with thicker (>750 nm) MHP layers exhibit poor performance owing to competing nonradiative charge recombination in a “dead‐volume” of MHP. Overall, these findings demonstrate the need for fine control over MHP thickness to achieve the highest efficiency cells, and accurate consideration of photon reabsorption, optical interference, and charge transport properties.     

Analysis of humeral head displacements from sequences of biplanar X-rays: repeatability study and preliminary results in healthy subjects

This work presents an accurate method to measure gleno-humeral translations in a controlled pseudo-kinematic environment. Low-dose biplanar X-rays were acquired from nine healthy subjects at three elevations of the arm in the scapular plane. On each set of images, shoulder bony landmarks were manually located in 3D using a dedicated software. Intra-observer and inter-observer repeatability of landmark identification, as well as humeral head center (GH) translations, were studied. Repeatability for the identification of GH in the global coordinate system (CS) was good with 95% confidence intervals (CIs) ranging from 0.57 to 2.25 mm. Scapular landmark CIs ranged from 0.80 to 12 mm. Gleno-humeral translations of small amplitude ( < 6 mm) were detected in seven out of nine subjects. The results obtained here confirm that calibrated low-dose stereo-radiography is a promising tool for the functional analysis of the shoulder.     

Optical Properties of Noncontinuous Gold Shell Engineered on Silica Mesosphere

The optical properties of individual noncontinuous shells with different gold coverage are investigated by the single-particle dark field scattering measurements and single-particle surface-enhanced Raman scattering (SERS) measurements at different excitation wavelengths. By controlling the growth of gold seeds, multi-metallic nanogaps/crevices with different optical responses are assembled on silica mesospheres forming noncontinuous shells that can be confirmed through the transmission electron microscope images. We find the surface plasmon resonance of single shell red-shifts from 510 to 680 nm with the increase of gold coverage. At the excitation of 532 and 785 nm, the best enhancements about 2.0?×?10⁵ and 1.1?×?10⁷ are obtained on spheres with ～60 and 83 % gold coverage, respectively. The weak polarization-dependent SERS indicates that the enhancement is from the multi-gaps on single noncontinuous shell. This optical tunable and SERS active noncontinuous gold shell can be applied in biosensing, ultra trace detection, and molecule analysis needing multi-wavelengths excitation.     

Extraordinary Optical Transmission Performances of Nanosandwiched Grating for Wideband Multi-Function Integration

In this paper, we present a peculiar metal-dielectric-metal (MDM) nanosandwich grating structure that can achieve extraordinary optical transmission performances at normal incidence in the ultraviolet-visible-near infrared (UV-VIS-NIR) regions. The proposed structure shows three obvious spectrum characteristics: it can obtain high transmittance up to 80 % in NUV region and efficiently blocking visible wavelengths for transverse-magnetic (TM) polarized incidence; a broadband NIR polarizer can be inspired in the wavelength range from 950 to 1400 nm; more surprisingly, these performances do not deteriorated until 30° tilting angle. Compared to other grating structures with single metal overlayer, it shows wider band-stop characteristics and higher broadband transmission transmittance and extinction ratio (ER) in the investigated wavebands. We analyze the underlying physical mechanism by using numerical simulation, which is primarily attributed to metal ultraviolet transparency, surface plasmon polariton (SPP) at metal/dielectric interface, Fabry–Perot (FP)-like cavity mode within this dielectric grating, and optical magnetic resonance especially in the dielectric interlayer of the MDM sandwiched structure. This structure is very important for developing high-performance subwavelength multifunctional integrated optical devices.     

Description of whistles of Irrawaddy dolphins (Orcaella brevirostris) from the waters of Matang,Peninsular Malaysia

The whistles of Irrawaddy dolphins (Orcaella brevirostris) from the waters of Matang, western Peninsular Malaysia are described. Duration, frequency and frequency modulation variables were measured from 163 whistles recorded using a broadband towed hydrophone. Irrawaddy dolphins produced whistles with a mean duration of 0.366 s (S.D. ± 0.217 s). The fundamental frequency of whistles extended from 3040 to 17,123 Hz with low levels of frequency modulation. These dolphins produced whistles that were comparable to those of conspecifics recorded from the waters of Kalimantan, but were generally different from the related Australian snubfin dolphin (O. heinsohni). They also differed from the whistles of the sympatric Indo-Pacific humpback dolphin (Sousa chinensis). Characteristics of Irrawaddy dolphin whistles may be useful in future passive acoustic monitoring studies to investigate differences in sympatric species and their habitat.     

Noninvasive in vivo monitoring of methemoglobin formation and reduction with broadband diffuse optical spectroscopy.

We present noninvasive, quantitative in vivo measurements of methemoglobin formation and reduction in a rabbit model using broadband diffuse optical spectroscopy (DOS). Broadband DOS combines multifrequency frequency-domain photon migration (FDPM) with time-independent near infrared (NIR) spectroscopy to quantitatively measure bulk tissue absorption and scattering spectra between 600 nm and 1,000 nm. Tissue concentrations (denoted by brackets) of methemoglobin ([MetHb]), deoxyhemoglobin ([Hb-R]), and oxyhemoglobin ([HbO2]) were determined from absorption spectra acquired in "real time" during nitrite infusions in nine pathogen-free New Zealand White rabbits. As little as 30 nM [MetHb] changes were detected for levels of [MetHb] that ranged from 0.80 to 5.72 microM, representing 2.2 to 14.9% of the total hemoglobin content (%MetHb). These values agreed well with on-site ex vivo cooximetry data (r2= 0.902, P < 0.0001, n = 4). The reduction of MetHb to functional hemoglobins was also carried out with intravenous injections of methylene blue (MB). As little as 10 nM changes in [MB] were detectable at levels of up to 150 nM in tissue. Our results demonstrate, for the first time, the ability of broadband DOS to noninvasively quantify real-time changes in [MetHb] and four additional chromophore concentrations ([Hb-R], [HbO2], [H2O], and [MB]) despite significant overlapping spectral features. These techniques are expected to be useful in evaluating dynamics of drug delivery and therapeutic efficacy in blood chemistry, human, and preclinical animal models.     

Fluorescence measurement by a streak camera in a single-photon-counting mode

We describe here a recently developed fluorescence measurement system that uses a streak camera to detect fluorescence decay in a single photon-counting mode. This system allows for easy measurements of various samples and provides 2D images of fluorescence in the wavelength and time domains. The great advantage of the system is that the data can be handled with ease; furthermore, the data are amenable to detailed analysis. We describe the picosecond kinetics of fluorescence in spinach Photosystem (PS) II particles at 4–77 K as a typical experimental example. Through the global analysis of the data, we have identified a new fluorescence band (F689) in addition to the already established F680, F685, and F695 emission bands. The blue shift of the steady-state fluorescence spectrum upon cooling below 77 K can be interpreted as an increase of the shorter-wavelength fluorescence, especially F689, due to the slowdown of the excitation energy transfer process. The F685 and F695 bands seem to be thermally equilibrated at 77 K but not at 4 K. The simple and efficient photon accumulation feature of the system allows us to measure fluorescence from leaves, solutions, single colonies, and even single cells. The 2D fluorescence images obtained by this system are presented for isolated spinach PS II particles, intact leaves of Arabidopsis thaliana, the PS I super-complex of a marine centric diatom, Chaetoceros gracilis, isolated membranes of a purple photosynthetic bacterium, Acidiphilium rubrum, which contains Zn-BChl a, and a coral that contains a green fluorescent protein and an algal endosymbiont, Zooxanthella.     

Effects of Refractive Index Variations on the Optical Transmittance Spectral Properties of the Nano-Hole Arrays

The 3D finite difference time domain technique was carried out to study the optical transmission properties of nano-hole arrays in the gold thin film supported by materials with different index of refraction in the visible and infrared regions. A series of perforated nano-hole structures on the gold film at different hole radius, hole depth of 100 nm, and structural periodicity of 400 nm were studied. It was found that transmission properties (i.e., intensity, FWHM, and resonance position) were strongly affected by hole radius and surrounding medium index of refraction. The maximum optical transmittance was observed as 31.9 % in a nano-hole array of hole radius of 125 nm and refractive index of 1.3. The maximum sensitivity of 300 nm/RIU was obtained at index of refraction of 1.7, whereas the minimum one was calculated as 110 nm/RIU in a nano-hole array of hole radius of 50 nm. It was also found that on increasing the hole radius from 50 to 125 nm, the spectral sensitivity was decreased, whereas the index sensitivity was increased on increasing the refractive index.     

Determination of the Optical Thickness of sub 10-nm Thin Metal Films by SPR Experiments

We discuss the experimental data of surface plasmon resonance (SPR) occurring at the interface between air and single and bimetallic thin layers of Au and Ag prepared on glass substrates. The bilayer configuration allowed for the measurements of the optical constants of metallic films that are ultra thin; e.g., below 10 nm of thickness since SPR modes on such thin films in a single-layer configuration are shallow. We also discuss the effect of film thickness on SPR coupling. Thickness and refractive index of the films were determined by matching experimental SPR curves to the theoretical ones. Thickness and roughness of the films were also measured by atomic force microscopy. The results obtained by experimental measurements are in good agreement with AFM analysis.     

Large Scale Fabrication of Gold Nano-Structured Substrates Via High Temperature Annealing and Their Direct Use for the LSPR Detection of Atrazine

The present work is reporting on the fabrication of localized surface plasmonic resonant (LSPR) gold nano-structures on glass substrate by using different high annealing temperatures (500 °C, 550 °C, 600 °C) of initially created semi-continue gold films (2 nm and 5 nm) by the electron beam evaporation technique. Interestingly, well-defined gold nano-structures were also obtained from continuous 8 nm evaporated gold film - known as the value above gold percolated thickness - once exposed to high temperatures. The surface morphology and plasmonic spectroscopy of “annealed” nano-structures were controlled by key experimental parameters such as evaporated film thickness and annealing temperature. By using scanning electron microscopy (SEM) characterization of annealed surface it was noticed that the size and inter-particle distance between nano-structures were highly dependent on the evaporated thin film thickness, while the nanoparticle shape evolution was mainly affected by the employed annealing temperature. Due to the well-controlled morphology of gold nano-particles, prominent and stable LSPR spectra were observed with good plasmon resonance tunability from 546 nm to 780 nm that recommend the developed protocol as a robust alternative to fabricate large scale LSPR surface. An example of a LSPR-immunosensor is reported. Thus, the monoclonal anti-atrazine antibodies immobilizion on the “annealed” gold nano-structures, as well as the specific antigen (atrazine) recognition were monitored as variations of the resonance wavelength shifts and optical density changes in the extinction measurements.     

Improved Absorbance and Near-Infrared Dispersion of AuGe Nanoparticles over Au Nanoparticles Prepared with Similar Thermal Annealing Environment

The difficulty in patterning the structures at sub-wavelength range leads to employ the bottom-up approach to form nanostructures of metals as well as dielectric components that disperse them in host media. The optical properties of nanoparticles are studied with UV-Vis 750 (lambda) NIR spectroscopy and fit with empirical relations. The refractive index is about the volume fraction of particles. The AuGe nanoparticles demonstrate improved absorbance, lower refractive index, and higher extinction than Au nanoparticles formed with similar thermal process. Surface plasmon resonance (SPR) phenomena are highly sensitive to the bonding between atoms, atomic structure, and the electronic configuration in atoms of the given material. If one takes into account the structure of materials, then the literature on eutectic alloys predicts that alloying gold with germanium (AuGe) with varying compositions will also change the x-ray diffraction peak positions of gold itself. The peak shift can be interpreted as the change in grain size or shift in grain boundaries implying a corresponding change in material’s atomic arrangement within lattice structure. As a result, there will be a change in the charge distribution of free electron cloud in original gold ultimately affecting a change in the plasmon resonance frequency and thereby modulating the various optical phenomena such as absorbance, reflectance, and refractive index. This alloying also brings a change in the dielectric constant of the material such that the plasmonic behavior may shift among different regions (UV, visible, NIR, MWIR, and LWIR). Metal semiconductor eutectic alloy which is widely popular as a soldering material would have scope in futuristic photonic applications due to its tuneable optical properties. In this work, we study the effects of Au and AuGe nanoparticle deposition on GaAs films grown by molecular beam epitaxy (MBE). Au and AuGe thin films (12-nm thick) were annealed in the temperature ranges of 400–800 and 300–700 °C, respectively, to form Au and AuGe nanoparticles. The formation of these nanoparticles was confirmed by scanning electron microscopy (SEM) measurements. Optical absorption spectroscopy measurements showed plasmon resonance peaks at around 670 and 535 nm for the AuGe-deposited 300 °C-annealed sample and Au-deposited 600 °C-annealed sample on sapphire, respectively, thereby confirming the plasmonic effect. Correlation of Raman spectroscopy measurement results with X-ray diffraction measurement results reveal that the transverse optical mode intensity and full width at half maximum of the GaAs (400) peak increased with an increase in annealing temperature, indicating degradation of the crystalline properties of GaAs film at higher annealing temperatures. The highest increments of the photoluminescence (PL) intensities in comparison to that of the bare GaAs film were observed to be 37 and 77% for the Au-deposited 600 °C-annealed and AuGe-deposited 300 °C-annealed samples, respectively. These enhancements of PL spectra are an indication of the significant scattering of photons by Au and AuGe nanoparticles, and they are attributed mainly to the contribution of the local surface plasmon resonance of these nanoparticles. A comparative analysis of PL enhancements revealed that AuGe nanoparticles induced a greater enhancement than Au nanoparticles. The calculated activation energies of the Au-deposited 600 °C-annealed sample, AuGe-deposited 300 °C-annealed sample, and bare GaAs sample were around 18, 24, and 33 meV, respectively. We found one-order increment in peak responsivity of AuGe plasmonic-based trilayer InAs quantum dot detector in comparison to as-grown detector at 80 K. Therefore, this study is expected to be very useful in the realization of high-performance plasmonic-based optoelectronic and sensing devices.     

Solid and Hollow Gold Nanostructures for Nanomedicine: Comparison of Photothermal Properties

The photothermal properties of solid and hollow gold nanostructures represented by colloidal solutions of spherical nanoparticles, nanoshells, and nanocages upon irradiation with a 100 mW 808 nm continuous-wave laser for the first time were experimentally compared under identical optical density and nanoparticle concentration conditions. Accompanying computer modeling of light absorption by the studied gold nanostructures revealed the general parameters influencing the photothermal efficiency, which is of significance for nanomedical applications. The spectral position of localized plasmonic excitations of the studied nanostructures ranged from 518 nm for solid gold nanoparticles to 718 nm for gold nanocages, which provided a possibility to observe a direct influence of the wavelength proximity between the localized surface plasmon resonance and laser line on the heat generation capability of the nanostructures. As a result, the best photothermal efficiency was registered for gold nanocages, which proves them as an efficient photothermal treatment agent and a possible candidate to build a nanocarrier platform for drug delivery with a controlled release. Light absorption modeling demonstrated an existence of optimal wall thickness for gold nanoshells that should lead to the maximum photothermal efficiency when irradiated with 808 nm light, which varied from about 0.1 to 0.4 in units of external nanoshell radius with an increase of the wall porosity. Additionally, computer modeling results show that increased wall porosity should lead to enhanced photothermal efficiency of polydisperse colloidal solutions of hollow gold nanostructures.     

Plasmonic Au-MoO<Subscript>3</Subscript> Colloidal Nanoparticles by Reduction of HAuCl<Subscript>4</Subscript> by Blue MoO<Subscript>x</Subscript> Nanosheets and Observation of the Gasochromic Property

Defective colloids of blue MoO_x nanosheets were prepared by anodizing exfoliation method in water. This colloidal solution exhibits an optical plasmonic absorption band in the infrared region at about 760 nm. Merely mixing HAuCl₄ solution with the MoO_x leads to loss of the blue color, decaying of 760 nm plasmonic peak and simultaneous formation of the gold plasmon absorption peak at 550–570 nm. Some spectral variations in gold plasmonic peak and MoO_x optical band gap were observed for Mo:Au ratio of 10:1, 20:1, 30:1, and 40:1. The size of the gold nanoparticles was in the 5–6 nm range with fcc crystalline structure. X-ray photoelectron spectroscopy (XPS) revealed that the initial solution contains Mo⁵⁺ states and hydroxyl groups, which after reduction, hydroxyl groups are eliminated and the Mo⁵⁺ states converted to Mo⁶⁺. The obtained Au-MoO₃ colloids have a gasochromic property in which they are colored back to blue in the presence of hydrogen gas and the molybdenum oxide absorption peak recovered again. Furthermore, it was observed that both gold and Mo oxide plasmonic peaks redshift by insertion of hydrogen gas which is attributed to change in solution refractive index and formation of defect concentration.     

Impact of I/D polymorphism of angiotensin-converting enzyme (ACE) gene on myocardial infarction susceptibility among young Moroccan patients

Objective

Our case–control study aimed to access the potential association of insertion/deletion (I/D) ACE (angiotensin converting enzyme) gene polymorphism with myocardial infarction (MI) risk of occurrence among a sample of Moroccan patients, especially young ones.

Results

Distribution of I/D ACE gene variant among cases vs controls, showed that healthy controls carried out higher frequency of wild type allele I compared to cases (23.5% vs 21.79% respectively), when cases were carrying higher frequency of mutant allele D (78.21% vs 76.5% for controls). Patients were-after this- divided into two groups of < 45 and > 55 years of age, to investigate whether or not younger patients carried out higher frequency of the mutant allele D, than older ones. As expected, < 45 years old patients carried out more DD genotype than older ones (68.9% vs 54.6% respectively), and higher frequency of mutant allele D (81.08% vs 75% respectively). Besides, a tendency to a positive association was found under the recessive genetic transmission model (OR [95% CI] = 1.85 [0.93–3.69], P = 0.08), suggesting that the I/D ACE polymorphism may be associated with MI occurrence among younger patients (< 45 years of age).