Silver Nanoparticle Effect on Spectral-Kinetic Properties of Thin Nickel Phthalocyanine Films

Plasmonics - We have investigated spectral and spectral-kinetic properties of hybrid plasmonic nanocomposites on silver nanoparticle monolayers and thin nickel phthalocyanine films. The...     

Dextran Nanoparticle Synthesis and Properties

Dextran is widely exploited in medical products and as a component of drug-delivering nanoparticles (NPs). Here, we tested whether dextran can serve as the main substrate of NPs and form a stable backbone. We tested dextrans with several molecular masses under several synthesis conditions to optimize NP stability. The analysis of the obtained nanoparticles showed that dextran NPs that were synthesized from 70 kDa dextran with a 5% degree of oxidation of the polysaccharide chain and 50% substitution with dodecylamine formed a NP backbone composed of modified dextran subunits, the mean diameter of which in an aqueous environment was around 100 nm. Dextran NPs could be stored in a dry state and reassembled in water. Moreover, we found that different chemical moieties (e.g., drugs such as doxorubicin) can be attached to the dextran NPs via a pH-dependent bond that allows release of the drug with lowering pH. We conclude that dextran NPs are a promising nano drug carrier.     

Microwave-Assisted Growth of Silver Nanoparticle Films with Tunable Plasmon Properties and Asymmetrical Particle Geometry for Applications as Radiation Sensors

We report a simple and fast microwave-assisted method to grow silver nanoparticle films with tunable plasmon resonance band. Microwaving time controls nucleation and growth as well as particle agglomeration, cluster formation, particle morphology, and the plasmonic properties. Films produced with times shorter than 30 s presented a single well-defined plasmon resonance band (~ 400 nm), whereas films produced with times longer than 40 s presented higher wavelength resonances modes (> 500 nm). Plasmon band position and intensity can be easily tuned by controlling microwaving time and power. SEM and AFM images suggested the growth of asymmetrical silver nanoparticles. Simulated extinction spectra considering particles as spheres, hemispheres, and spherical caps were performed. The films were employed to enhance the sensitivity of ionizing radiation detectors assessed by optically stimulated luminescence (OSL) via plasmon-enhanced luminescence. By tuning the plasmon resonance band to overlap with the OSL stimulation (530 nm), luminescence enhancements of greater than 100-fold were obtained, demonstrating the importance of tuning the plasmon resonance band to maximize the OSL intensity and detector sensitivity. This versatile method to produce silver nanoparticle films with tunable plasmonic properties is a promising platform for developing small-sized radiation detectors and advanced sensing technologies.

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Near-Infrared,Surface-Enhanced Fluorescence Using Silver Nanoparticle Aggregates in Solution

Fluorescence spectroscopy is used in many life science and clinical research diagnostic assays. Improvements in the sensitivity and limit-of-detection of these assays may have profound implications. Here, we demonstrate a near-infrared, surface-enhanced fluorescence technology that increases the signal of IRDye 800CW-labeled streptavidin by up to 2,530-fold while improving the limit-of-detection 1,000-fold. Citrate-stabilized, silver nanoparticles that aggregate in solution were used with the dye-protein conjugate to form plasmon-active nanostructures. The technique is straightforward to implement and fully compatible with commercially available immunoassay instrumentation and consumables.     

SERS Study of Tetrodotoxin (TTX) by Using Silver Nanoparticle Arrays

The optical properties of tetrodotoxin (TTX), a scarce toxin with anesthetic properties, were studied using nanoparticle arrays-assisted surface-enhanced Raman scattering (SERS). The nanoparticles arrays were fabricated using nanosphere lithography and a metallic lift-off process to control the particle size, shape, and spacing in the arrays. Using density functional methods, the Raman spectrum of TTX was also calculated with Gaussian03 software. The main peaks of the spectrum are originated from the vibration of the NH₂ molecule group. In the SERS experiment, we were able to measure the Raman spectrum with a TTX concentration as less as 0.9 ng/mL. This sensitivity is comparable to that from high performance liquid chromatography.     

Silver Nanoparticle Arrays on a DVD-Derived Template: An easy&cheap SERS Substrate

Commercially available digital versatile discs (DVDs) contain a silver-coated spiral distribution of rectangular-shaped grooves (AgDVD): for the first time, they have been used to produce surface-enhanced Raman scattering (SERS) substrates by electrochemical deposition of silver nanoparticles (AgNPs@AgDVD). The overall procedure only requires cheap and widely available materials and can be easily accomplished. Scanning electron microscopy images of AgNPs@AgDVD revealed that small AgNPs (average diameter about 15 nm) are present within the valleys of AgDVD, whereas over the ridges, the AgNPs are bigger, more densely packed and with a dendrite-like morphology somewhere. The SERS properties of these substrates have been studied in terms of the enhancement factor (EF), point-to-point reproducibility and sample-to-sample repeatability. It turned out that high SERS EF and good reproducibility requirements are both fulfilled. As for repeatability, remarkably better results than typical literature values have been achieved. Such an easy&cheap preparation along with efficient SERS properties make DVD-derived SERS substrates very good candidates for the development of convenient and disposable sensing platforms.     

Tuning Colors of Silver Nanoparticle Sheets by Multilayered Crystalline Structures on Metal Substrates

We report a new concept of tuning plasmonic colors of two-dimensional crystalline silver nanoparticle sheets with layer-by-layer structures. The multilayered crystalline sheets fabricated by the Langmuir–Schaefer method keep the localized surface plasmon resonance bands at the same position (λ _max?=?465 nm) on quartz, while they change their colors drastically on metal substrates depending on the number of layers (one to five layers). The response of the absorption spectra was absolutely nonlinear, with maximum absorption for two or three layers. The obtained results were well reproduced by the finite difference time domain simulation. The simulation confirmed that these plasmonic colors originate not only from near-field coupling of plasmon resonance but also far-field nano-optics of the multilayered silver nanoparticle sheets.     

Effects of Silver Nanoparticle Exposure on Germination and Early Growth of Eleven Wetland Plants

The increasing commercial production of engineered nanoparticles (ENPs) has led to concerns over the potential adverse impacts of these ENPs on biota in natural environments. Silver nanoparticles (AgNPs) are one of the most widely used ENPs and are expected to enter natural ecosystems. Here we examined the effects of AgNPs on germination and growth of eleven species of common wetland plants. We examined plant responses to AgNP exposure in simple pure culture experiments (direct exposure) and for seeds planted in homogenized field soils in a greenhouse experiment (soil exposure). We compared the effects of two AgNPs–20-nm polyvinylpyrrolidine-coated silver nanoparticles (PVP-AgNPs) and 6-nm gum arabic coated silver nanoparticles (GA-AgNPs)–to the effects of AgNO₃ exposure added at equivalent Ag concentrations (1, 10 or 40 mg Ag L⁻¹). In the direct exposure experiments, PVP-AgNP had no effect on germination while 40 mg Ag L⁻¹ GA-AgNP exposure significantly reduced the germination rate of three species and enhanced the germination rate of one species. In contrast, 40 mg Ag L⁻¹ AgNO₃ enhanced the germination rate of five species. In general root growth was much more affected by Ag exposure than was leaf growth. The magnitude of inhibition was always greater for GA-AgNPs than for AgNO₃ and PVP-AgNPs. In the soil exposure experiment, germination effects were less pronounced. The plant growth response differed by taxa with Lolium multiflorum growing more rapidly under both AgNO₃ and GA-AgNP exposures and all other taxa having significantly reduced growth under GA-AgNP exposure. AgNO₃ did not reduce the growth of any species while PVP-AgNPs significantly inhibited the growth of only one species. Our findings suggest important new avenues of research for understanding the fate and transport of NPs in natural media, the interactions between NPs and plants, and indirect and direct effects of NPs in mixed plant communities.     

Influence of Material Properties on TiO2 Nanoparticle Agglomeration

Emerging nanomaterials are being manufactured with varying particle sizes, morphologies, and crystal structures in the pursuit of achieving outstanding functional properties. These variations in these key material properties of nanoparticles may affect their environmental fate and transport. To date, few studies have investigated this important aspect of nanoparticles'' environmental behavior. In this study, the aggregation kinetics of ten different TiO₂ nanoparticles (5 anatase and 5 rutile each with varying size) was systematically evaluated. Our results show that, as particle size increases, the surface charge of both anatase and rutile TiO₂ nanoparticles shifts toward a more negative value, and, accordingly, the point of zero charge shifts toward a lower value. The colloidal stability of anatase sphere samples agreed well with DLVO theoretical predictions, where an increase in particle size led to a higher energy barrier and therefore greater critical coagulation concentration. In contrast, the critical coagulation concentration of rutile rod samples correlated positively with the specific surface area, i.e., samples with higher specific surface area exhibited higher stability. Finally, due to the large innate negative surface charge of all the TiO₂ samples at the pH value (pH = 8) tested, the addition of natural organic matter was observed to have minimal effect on TiO₂ aggregation kinetics, except for the smallest rutile rods that showed decreased stability in the presence of natural organic matter.     

Computational Multiscale Toxicodynamic Modeling of Silver and Carbon Nanoparticle Effects on Mouse Lung Function

A computational, multiscale toxicodynamic model has been developed to quantify and predict pulmonary effects due to uptake of engineered nanomaterials (ENMs) in mice. The model consists of a collection of coupled toxicodynamic modules, that were independently developed and tested using information obtained from the literature. The modules were developed to describe the dynamics of tissue with explicit focus on the cells and the surfactant chemicals that regulate the process of breathing, as well as the response of the pulmonary system to xenobiotics. Alveolar type I and type II cells, and alveolar macrophages were included in the model, along with surfactant phospholipids and surfactant proteins, to account for processes occurring at multiple biological scales, coupling cellular and surfactant dynamics affected by nanoparticle exposure, and linking the effects to tissue-level lung function changes. Nanoparticle properties such as size, surface chemistry, and zeta potential were explicitly considered in modeling the interactions of these particles with biological media. The model predictions were compared with in vivo lung function response measurements in mice and analysis of mice lung lavage fluid following exposures to silver and carbon nanoparticles. The predictions were found to follow the trends of observed changes in mouse surfactant composition over 7 days post dosing, and are in good agreement with the observed changes in mouse lung function over the same period of time.     

Optical Properties of Silver Hollow Triangular Nanoprisms

The extinction spectra and electric field distributions of hollow triangular nanoprisms are calculated using the discrete dipole approximation method and compared with those of the solid triangular nanoprisms. When light propagates along the prisms, the main plasmon peaks of hollow triangular nanoprisms red shift compared with those of the solid triangular nanoprisms. At the main plasmon peaks, the hollow triangular nanoprisms provide more hot spots than the solid triangular nanoprisms. Therefore, the hollow triangular nanoprisms are more surface-enhanced Raman scattering active than the solid triangular prisms and can be used to detect small amount of molecules. For the hollow triangular nanoprism, although the local electric field distribution extremely relates to the incident polarization, the extinction spectra are independent of the incident polarization. In addition, the main plasmon peaks red shift linearly with the edge length, while they blue shift exponentially with the increase of the thickness of the hollow triangular nanoprisms. These results could be used to engineer hollow triangular nanoprisms for specific plasmonic applications.     

Plasmonic Properties of Silver Nanoparticles on Two Substrates

In this paper, we examine the plasmonic properties of silver nanoparticles, with an emphasis on the sensitivity of the extinction spectra on the supporting substrate: silica (SiO₂) microsphere and indium tin oxide (ITO) coated glass slide, on which silver particles are deposited electroless and electrochemically, respectively. The microstructures and phases of these nanoparticles are characterized by transmission electron microscopy, field emission electron microscopy and X-ray diffraction analysis. The surface plasmon resonance (SPR) properties which are experimentally measured in the ultraviolet-visible-near infrared spectral region are compared to electrodynamics calculations based on the discrete dipole approximation. A wide SPR band ranging from 400 to 800 nm is observed for the silver nanoparticles on a silica microsphere, which is similar to the plasmon resonance characteristics of metal nanoshells. The SPR of a conducting substrate, however, has an effect on the plasmonic properties of silver nanoparticles at longer wavelength.      

Electromagnetic Field Propagation in the One-Dimensional Silver Nanoparticle Dimer Chains: Hotspots and Energy Transport

Strong local electromagnetic (EM) fields and efficient EM energy transport in metallic nanostructures are two important issues in their applications in quantum computations/communications. We investigate the propagation characteristics of the hotspots in one-dimensional silver nanoparticle dimer chains, which combine the functions of the gap field enhancement and the waveguide. The near field and the far field induced interplay among the local field enhancement, the radiative interaction, and the dissipation affects significantly the EM field transport efficiency. Moreover, the correlation between local structure and global structure leads to the structure-dependent excitation. With the help of the combined effects of the structure-dependent excitation, the field confinement and the propagation, the efficient EM field excitation, and long-range propagation can be obtained by tuning the structure of our systems. With suitable geometric parameters (dimer orientations, dimer gap sizes) of our system, the electric field intensity at the position 5000 nm away from the starting point (exciting point) is about 50 times of the corresponding field intensity in a silver nanoparticle chain.

     

Optimization of Dielectric-Coated Silver Nanoparticle Films for Plasmonic-Enhanced Light Trapping in Thin Film Silicon Solar Cells

Surface plasmonic-enhanced light trapping from metal nanoparticles is a promising way of increasing the light absorption in the active silicon layer and, therefore, the photocurrent of the silicon solar cells. In this paper, we applied silver nanoparticles on the rear side of polycrystalline silicon thin film solar cell and systematically studied the dielectric environment effect on the absorption and short-circuit current density (Jsc) of the device. Three different dielectric layers, magnesium fluoride (MgF₂, n?=?1.4), tantalum pentoxide (Ta₂O₅, n?=?2.2), and titanium dioxide (TiO₂, n?=?2.6), were investigated. Experimentally, we found that higher refractive index dielectric coatings results in a redshift of the main plasmonic extinction peak and higher modes were excited within the spectral region that is of interest in our thin film solar cell application. The optical characterization shows that nanoparticles coated with highest refractive index dielectric TiO₂ provides highest absorption enhancement 75.6 %; however, from the external quantum efficiency characterization, highest short-circuit current density Jsc enhancement of 45.8 % was achieved by coating the nanoparticles with lower refractive index MgF₂. We also further optimize the thickness of MgF₂ and a final 50.2 % Jsc enhancement was achieved with a 210-nm MgF₂ coating and a back reflector.     

Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles

Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multi-layered Mie theory were studied, and interesting trends were observed.

     

Review on the Optical Properties of Nanoparticle Aggregates Towards the Therapeutic Applications

Plasmonics - Nanoparticles are of potential use for therapeutic applications, and nowadays a variety of modalities involving optical characteristics of nanoparticles are in the clinical translation...     

Modifying and Fine Controlling of Silver Nanoparticle Nucleation Sites and SERS Performance by Double Silicon Etching Process

Different forms of modified and well-controlled plasmonic silver nanoparticles (AgNPs) were synthesized by silver ion reduction process of porous silicon (PS). Fine control of PS surface morphology was accomplished by employing two etching processes: light-induced etching (LIE) and photo electrochemical etching (PECE). The idea was to prepare excellent and reproducible surface-enhanced Raman scattering (SERS) substrates with high enhancement performance. PS surface modification was employed to create efficient and nearly uniformly distributed AgNP hotspot regions with very high specific surface areas. Reproducibility deviation of no more than 5% and enhancement factor of 1.2 × 10¹⁴ were obtained by SERS measurements at very low, rhodamine 6G (R6G) dye, concentration 10^?15 M. The PS morphology SERS substrate was well discussed and analyzed using field emission scanning electron microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), and Raman measurements.     

Total Internal Reflection Accounts for the Bright Color of the Saharan Silver Ant

The Saharan silver ant Cataglyphis bombycina is one of the terrestrial living organisms best adapted to tolerate high temperatures. It has recently been shown that the hairs covering the ant’s dorsal body part are responsible for its silvery appearance. The hairs have a triangular cross-section with two corrugated surfaces allowing a high optical reflection in the visible and near-infrared (NIR) range of the spectrum while maximizing heat emissivity in the mid-infrared (MIR). Those two effects account for remarkable thermoregulatory properties, enabling the ant to maintain a lower thermal steady state and to cope with the high temperature of its natural habitat. In this paper, we further investigate how geometrical optical and high reflection properties account for the bright silver color of C. bombycina. Using optical ray-tracing models and attenuated total reflection (ATR) experiments, we show that, for a large range of incidence angles, total internal reflection (TIR) conditions are satisfied on the basal face of each hair for light entering and exiting through its upper faces. The reflection properties of the hairs are further enhanced by the presence of the corrugated surface, giving them an almost total specular reflectance for most incidence angles. We also show that hairs provide an almost 10-fold increase in light reflection, and we confirm experimentally that they are responsible for a lower internal body temperature under incident sunlight. Overall, this study improves our understanding of the optical mechanisms responsible for the silver color of C. bombycina and the remarkable thermoregulatory properties of the hair coat covering the ant’s body.