The Effect of Ag Nanoparticles on Surface-Enhanced Luminescence from Au Nanovoid Arrays

Studies comparing the effect of adding two different nanoparticle compositions on the plasmonic properties of Au nanovoid arrays were undertaken. Surface-enhanced resonance luminescence and surface-enhanced resonance Raman studies comparing dispersed Ag nanoparticles and Ag nanoparticle aggregates on gold nanovoid arrays were undertaken. These studies showed that using Ag nanoparticle aggregates increased both luminescence and Raman efficiency relative to when dispersed nanoparticles were used; in addition, these studies also showed that adding dispersed Ag nanoparticles supported a more reproducible enhancement in luminescence and Raman across the substrate compared to using Ag nanoparticle aggregates. Finite element analysis simulations indicated that surface plasmon polariton distribution in the sample was affected by the presence of the Ag nanoparticles on the Au nanovoid array.     

Ultrasensitive electrochemical detection of Bacillus thuringiensis transgenic sequence based on in situ Ag nanoparticles aggregates induced by biotin-streptavidin system

A novel electrochemical biosensor was developed for detecting short DNA oligonucleotide of Bacillus thuringiensis (Bt) transgenic sequence based on Ag nanoparticle aggregates. To fabricate this DNA biosensor, the thiol-modified capture DNA (cDNA) was first anchored on gold (Au) electrode, and then the target DNA (tDNA) was hybridized with the immobilized cDNA. Subsequently, the probe DNA (pDNA) functionalized by biotinylated Ag nanoparticle was associated with the fixed tDNA, and the single Ag nanoparticle label was obtained (cited as SAg label). Finally, dissociative biotinylated Ag nanoparticle was bound to the resultant biotinylated SAg label assembled on Au electrode by virtue of bridge molecule streptavidin (SA) through biotin-SA specific interaction, which could lead to in situ aggregate of Ag nanoparticles on Au electrode and induce a novel tag including multiple Ag nanoparticles (cited as MAg tag). The novel tag exhibited excellent electroactive property in the solid-state Ag/AgCl process and was successfully applied to Bt transgenic sequence assay. A detection limit of 10 fM was achieved, which was improved by three orders of magnitude as compared to the SAg label. Furthermore, this novel DNA biosensor demonstrated a good selectivity towards tDNA.     

Enhanced Optical Forces and Tunable LSPR of Ag Triangular Nanoplates for Plasmonic Tweezers

Plasmonics - In this work, we present a plasmonic platform capable of the enhanced electric field (E-field) intensity, tunable LSPR effect, and trapping nanoparticles in different...     

Optical Modeling of Plasmonic Nanoparticles Enhanced Light Emission of Silicon Light-Emitting Diodes

Significant enhancement of radiative efficiency of thin-film silicon light-emitting diodes achieved by placing the active layer in close proximity to silver (Ag) nanoparticles has been observed. In this paper, optical properties including transmission, reflection, and absorption of a random assembly of Ag nanoparticles are theoretically investigated using the effective medium model. Furthermore, the influence of Ag nanoparticles on light emission of silicon light-emitting diodes is studied by an improved effective mode volume model we propose here. The normalized line shape of dipole oscillation is calculated directly using Lorentz–Drude model without using any approximation. Thus, it results in more accurate calculation of the enhanced Purcell factor in comparison with the conventional approach. We show that an enhancement of radiative efficiency of silicon light-emitting diodes can be achieved by localized surface plasmons on metal nanoparticles. The calculated result of optimal Ag nanoparticle size to enhance light emission of silicon light-emitting diodes at 900 nm wavelength is in very good agreement with those obtained from the experimental result. The model is useful for the design of metallic nanoparticles enhanced light emitters.     

Investigations on the Thermal Stability of Fullerene-Based (Ag-C<Subscript>70</Subscript>) Nanocomposite Thin Films

Fullerene-based bi-functional nanocomposite thin film (Ag nanoparticles embedded in fullerene C₇₀ matrix) is synthesized by thermal co-deposition method. Thermal stability of Ag-C₇₀ nanocomposite is investigated by annealing the nanocomposite thin film at different temperatures from 80 to 350 °C for 30 min. Optical and structural properties of nanocomposite thin film with respect to high temperature are studied by UV-visible spectroscopy and x-ray diffraction, respectively. Transmission electron microscopy is performed to observe the temperature-dependent size evolution of Ag nanoparticles in fullerene C₇₀ matrix. A large growth of Ag nanoparticles is observed with temperature especially above 200 °C due to enhanced diffusion of Ag in fullerene C₇₀ at higher temperature and Ostwald ripening. The properties of metal-fullerene nanocomposite is not significantly affected up to a temperature of 150 °C. With a further increase in temperature, a major blue shift of ~?33 nm in SPR wavelength is seen at a temperature of 300 °C due to the thermal induced structural transformation of fullerene C₇₀ matrix into amorphous carbon. A very large-sized Ag nanoparticle with a wide size distribution varying from 27.8 ± 0.6 to 330.0 ± 4.5 nm is seen at 350 °C and due to which, a red shift of ~?16 nm is obtained at this temperature. This study throws light on the thermal stability of the devices based on metal-fullerene bi-functional nanocomposite.     

Growth and fragmentation of silver nanoparticles in their synthesis with a fs laser and CW light by photo-sensitization with benzophenone.

The photo-sensitization synthetic technique of making silver nanoparticles using benzophenone is studied using both a laser and a mercury lamp as light sources. The power and irradiation time dependence of the synthesized nanoparticle absorption spectra and their size distribution [as determined by transmission electron microscopy (TEM)] are studied in each method and compared. In the laser synthesis, as either the laser power or the irradiation time increases, the intensity of the surface plasmon resonance absorption at 400 nm is found to increase linearly first, followed by a reduction of the red edge of the plasmon resonance absorption band. The TEM results showed that in the laser synthesis low powers and short irradiation times produce nanoparticles around 20 nm in diameter. Increasing the power or irradiation time produces a second population of nanoparticles with average size of 5 nm in diameter. These small particles are believed to be formed from the surface ablation of the large particles. The surface plasmon absorption band is found to be narrower when the nanoparticles are produced with laser irradiation. Throughout the exposure time with the CW lamp, the plasmon resonance absorption band of the particles formed first grows in intensity, then blue shifts and narrows, and finally red shifts while decreasing in intensity. The TEM results for lamp samples showed particle formation and growth, followed by small nanoparticle formation. The above results are discussed in terms of a mechanism in which, the excited benzophenone forms the ketal radical, which reduces Ag+ in solution and on the Ag nanoparticle surface. As the time of irradiation or the light energy increases the benzophenone is consumed, which is found to be the limiting reagent. This stops the formation of the normal large nanoparticles while their photo-ablation continues to make the small particles.     

Resonant Broadband Field Enhancement in Cylindrical Plasmonic Structure Surrounded by Perovskite Environment

We demonstrate the optical response of metal nanoparticles and their interaction with organic-inorganic perovskite (methyl ammonia lead halide (CH₃NH₃PbI₃)) environment using discrete dipole approximation (DDA) simulation technique. Important optical properties like absorption, scattering, and electric field calculations for metal nanoparticle using different geometry have been analyzed. The metal nanoparticles embedded in the perovskite media strongly support surface plasmon resonances (SPRs). The plasmonic interaction of metal nanoparticles with perovskite matrix is a strong function of MNP’s shape, size, and surrounding environment that can manipulate the optical properties considerably. The cylindrical shape of MNPs embedded in perovskite environment supports the SPR which is highly tunable to subwavelength range of 400–800 nm. Wide range of particle sizes has been selected for Ag, Au, and Al spherical and cylindrical nanostructures surrounded by perovskite matrix for simulation. The chosen hybrid material and anisotropy of structure together make a complex function for resonance shape and width. Among all MNPs, 70-nm spherical silver nanoparticle (NP) and cylindrical Ag NP having diameter of 50 nm and length of 70 nm (aspect ratio 1.4) generate strong electric field intensity that facilitates increased photon absorption. The plasmonic perovskite interaction plays an important role to improve the absorption of photon inside the thin film perovskite environment that may be applicable to photovoltaics and photonics.

     

Core–shell silver nanoparticles for optical labeling of cells

Silver nanoparticles have been modified with self-assembled monolayers of hydroxyl-terminated long chain thiols and encapsulated with a silica shell. The resulting core–shell nanoparticles were used as optical labels for cell analysis using flow cytometry and microscopy. The excitation of plasmon resonances in nanoparticles results in strong depolarized scattering of visible light, permitting detection at the single nanoparticle level. The nanoparticles were modified with neutravidin via epoxide–azide coupling chemistry, to which biotinylated antibodies targeting cell surface receptors were bound. The nanoparticle labels exhibited long-term stability in solutions with high salt concentrations without aggregation or silver etching. Labeled cells exhibited two orders of magnitude enhancement of the scattering intensity compared with unlabeled cells.     

InGaN/GaN MQW Photoluminescence Enhancement by Localized Surface Plasmon Resonance on Isolated Ag Nanoparticles

Spectroscopic study of photoluminescence (PL) enhancement due to the coupling of the light emitters in InGaN/GaN multiple quantum wells (MQWs) with the localized surface plasmon (LSP) resonance on silver (Ag) nanoparticles (NPs) is performed using the confocal microscopy and scanning near-field optical microscopy (SNOM) techniques. The paper is focused on revealing the emission enhancement due to coupling with a single metal nanoparticle. The enhancement is confirmed by time-resolved study of differential transmission (DT). The enhancement suppression caused by potential fluctuations due to the variations of indium content and quantum well (QW) width is also studied. A strong photoexcitation intensity dependence of the emission enhancement due to spectral runaway of the MQW emission from the resonance as carrier density increases is observed both in spatially integrated spectra and in the vicinity of a single nanoparticle.     

Coexistence of Plasmonic and Magnetic Properties in Bimetallic Fe/Ag Nanoparticles Synthesized by Pulsed Laser Ablation

Fe20:Ag80, Fe50:Ag50, and Fe80:Ag20 bimetallic nanoparticles were prepared with laser ablation method applied on Fe/Ag/polyvinyl alcohol (PVA) composite, at two different ablation times (20 and 50 min). The ratio of Fe with respect to Ag atoms as well as ablation time affect wavelength, intensity, and width of plasmon absorption peak. Increase in Fe content leaded to a redshift and a decrease in intensity and an increase in the width of plasmon absorption peaks. The transmission electron microscopy (TEM) analysis showed three kinds of grains which are Ag nanoparticles, Ag/Fe core/shells and Fe nanoparticles. Due to the concentration of Fe nanoparticles with the size of less than 5 nm around Ag ones with the size of 20 to 30 nm, a core–shell structure of these two metals forms and this decreases Ag plasmon resonance frequency, and as a result, its absorption peak has a redshift. According to the results of vibrating sample magnetometer (VSM), the Fe/Ag bimetallic nanoparticles were superparamagnetic.

     

Fluorescence enhancement monitoring of pyrromethene laser dyes by metallic Ag nanoparticles

Fluorescence enhancement monitoring of pyrromethene laser dyes using their complexation with Ag nanoparticles (Ag NPs) was studied. The size of the prepared Ag NPs was determined by transmission electron spectroscopy and UV/Vis absorption spectroscopy. Mie theory was also used to confirm the size of NPs theoretically. The effect of different nanoparticle concentrations on the optical properties of 1 × 10^‐4 M PM dyes shows that 40%of Ag NPs concentration (40%C Ag NPs) in complex is the optimum concentration. Also, the effects of different concentrations of PM dyes in a complex was measured. Emission enhancement factors were calculated for all samples. Fluorescence enhancement efficiencies depended on the input pumping energy of a Nd‐YAG laser (wavelength 532 nm and 8 ns pulse duration) were reported and showed the lowest energy (28 and 32 mJ) in the case of PM567 and PM597, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface Plasmon-Enhanced Spontaneous Emission from InGaN/GaN Multiple Quantum Wells by Indium Nanoparticles Fabricated Using Nanosphere Lithography

Economic nanofabrication of Ag, Al, Au nanotriangle arrays and In nanoparticle arrays are demonstrated using nanosphere lithography. The sizes of the nanoparticles are precisely tuned when nanospheres with different diameters are used. Localized surface plasmon resonances (LSPR) of the nanoparticle arrays are observed to be strongly dependent on their sizes and the LSPR of In nanoparticle arrays with various sizes cover the whole visible spectrum. By placing In nanoparticle arrays near the InGaN/GaN multiple quantum wells (MQWs), enhanced spontaneous emission is observed when the LSPR of the In nanoparticles matches the emission wavelength of InGaN/GaN MQWs.     

Real-time probing of membrane transport in living microbial cells using single nanoparticle optics and living cell imaging

Membrane transport plays a leading role in a wide spectrum of cellular and subcellular pathways, including multidrug resistance (MDR), cellular signaling, and cell-cell communication. Pseudomonas aeruginosa is renowned for its intriguing membrane transport mechanisms, such as the interplay of membrane permeability and extrusion machinery, leading to selective accumulation of specific intracellular substances and MDR. Despite extensive studies, the mechanisms of membrane transport in living microbial cells remain incompletely understood. In this study, we directly measure real-time change of membrane permeability and pore sizes of P. aeruginosa at the nanometer scale using the intrinsic color index (surface plasmon resonance spectra) of silver (Ag) nanoparticles as the nanometer size index probes. The results show that Ag nanoparticles with sizes ranging up to 80 nm are accumulated in living microbial cells, demonstrating that these Ag nanoparticles transport through the inner and outer membrane of the cells. In addition, a greater number of larger intracellular Ag nanoparticles are observed in the cells as chloramphenicol concentration increases, suggesting that chloramphenicol increases membrane permeability and porosity. Furthermore, studies of mutants (nalB-1 and DeltaABM) show that the accumulation rate of intracellular Ag nanoparticles depends on the expression level of the extrusion pump (MexAB-OprM), suggesting that the extrusion pump plays an important role in controlling the accumulation of Ag nanoparticles in living cells. Moreover, the accumulation kinetics measured by Ag nanoparticles are similar to those measured using a small fluorescent molecule (EtBr), eliminating the possibility of steric and size effects of Ag nanoparticle probes. Susceptibility measurements also suggest that a low concentration of Ag nanoparticles (1.3 pM) does not create significant toxicity for the cells, further validating that single Ag nanoparticles (1.3 pM) can be used as biocompatible nanoprobes for the study of membrane transport kinetics in living microbial cells.     

Plasmonic and Nonlinear Optical Absorption Properties of Ag:ZrO2 Nanocomposite Thin Films

Ag nanoparticles (NPs) embedded in a zirconium oxide matrix in the form of Ag:ZrO₂ nanocomposite (NC) thin films were synthesized by using the sol–gel technique followed by thermal annealing. With the varying of the concentration of Ag precursor and annealing conditions, average sizes (diameters) of Ag nanoparticles (NPs) in the nanocomposite film have been varied from 7 to 20 nm. UV–VIS absorption studies reveal the surface plasmon resonance (SPR)-induced absorption in the visible region, and the SPR peak intensity increases with the increasing of the Ag precursor as well as with the annealing duration. A red shift in SPR peak position with the increase in the Ag precursor concentration confirms the growth of Ag NPs. Surface topographies of these NC films showed that deposited films are dense, uniform, and intact during the variation in annealing conditions. The magnitude and sign of absorptive nonlinearities were measured near the SPR of the Ag NPs with an open-aperture z-scan technique using a nanosecond-pulsed laser. Saturable optical absorption in NC films was identified having saturation intensities in the order of 10¹² W/m². Such values of saturation intensities with the possibility of size-dependent tuning could enable these NC films to be used in nanophotonic applications.     

Optical and Thermal Enhancement of Plasmonic Nanofluid Based on Core/Shell Nanoparticles

The plasmonic effect is introduced in solar thermal areas to enhance light harvest and absorption. The optical properties of plasmonic nanofluid are simulated by finite difference time domain (FDTD) method. Due to the excitation of localized surface plasmon resonance (LSPR) effect, an intensive absorption peak is observed at 0.5 μm. The absorption characteristics are sensitive to particle size and concentration. As the particle size increases, the absorption peak is broadened and shifted to longer wavelength. The absorption of SiO₂/Ag plasmonic nanofluid is improved gradually as the volume concentration increases, especially in the UV region. The absorption edge is shifted from 0.6 to 1.0 μm as the volume concentration increases from 0.001 to 0.01. The thermal simulation of suspended SiO₂/Ag nanoparticle shows a uniform temperature rise of 17.91 K under solar irradiation (AM 1.5), while under the same condition, the temperature rises in Ag nanoparticle and Al nanoparticle are 11.12 and 5.39 K, respectively. The core/shell plasmonic nanofluid exhibits a higher photothermal performance, which has a potential application in photothermal areas. A higher temperature rise can be obtained by improving the incident light intensity or optical absorption properties of nanoparticles.     

Isoxyl Aerosols for Tuberculosis Treatment: Preparation and Characterization of Particles

Isoxyl is a potent antituberculosis drug effective in treating various multidrug-resistant strains in the absence of known side effects. Isoxyl has been used exclusively, but infrequently, via the oral route and has exhibited very poor and highly variable bioavailability due to its sparing solubility in water. These properties resulted in failure of some clinical trials and, consequently, isoxyl’s use has been limited. Delivery of isoxyl to the lungs, a major site of Mycobacterium tuberculosis infection, is an attractive alternative route of administration that may rescue this abandoned drug for a disease that urgently requires new therapies. Particles for pulmonary delivery were prepared by antisolvent precipitation. Nanofibers with a width of 200 nm were obtained by injecting isoxyl solution in ethanol to water at a volume ratio of solvent to antisolvent of 1:5. Based on this preliminary result, a well-controlled method, involving nozzle mixing, was employed to prepare isoxyl particles. All the particles were 200 to 400 nm in width but had different lengths depending on properties of the solvents. However, generating these nanoparticles by simultaneous spray drying produced isoxyl microparticles (Feret’s diameter, 1.19–1.77 μm) with no discernible nanoparticle substructure. The bulking agent, mannitol, helped to prevent these nanoparticles from agglomeration during process and resulted in nanoparticle aggregates in micron-sized superstructures. Future studies will focus on understanding difference of these isoxyl microparticles and nanoparticles/nanoparticle aggregates in terms of in vivo disposition and efficacy.     

On Optical Properties of Dilute Colloidal Gold

Wavelength-dependent complex effective refractive index of dilute colloidal gold, i.e., spherical gold nanoparticles in water was measured using a reflectometer and a spectrophotometer. The spectral data obtained was used for the calculation of the wavelength-dependent complex permittivity of the gold nanoparticle with the aid of the Maxwell Garnett effective medium model for the colloid. It is shown that the wavelength-dependent complex permittivity of gold nanoparticle is different from the complex permittivity of bulk gold. Furthermore, Smakula’s formula is introduced for the calculation of the relative concentration of gold nanoparticles embedded in liquid using absorption data of the colloid.     

Phase-Transfer Identification of Core-Shell Structures in Bimetallic Nanoparticles

On the basis of a combination of previously published experimental procedures, ultraviolet–visible spectroscopy, transmission electron microscopy, and energy-dispersive X-ray measurements, a systematic investigation was carried out on the phase-transfer characteristics of different bimetallic nanoparticles (Ag–Au, Ag–Pt, Ag–Ru, Au–Pt, Au–Ru, and Pt–Ru) formed by the seed-mediated growth reactions. The different phase-transfer characteristics of the monometallic nanoparticles of Au, Ag, Pt, and Ru were used to form the basis of differentiation between various possible structures existing in the bimetallic systems (core-shell particles or a physical mixture of nanoparticles). The experimental results indicate clearly the formation of core-shell nanoparticles of Ag–Au, Ag–Pt, Ru–Ag, Pt–Au, Au–Ru, and Pt–Ru when the nanoparticles of the first metal were used as the seeds in the seed-mediated growth reactions. However, when the order of the synthesis was reversed using the nanoparticles of the second metal as the seeds, only a physical mixture of the two metal nanoparticles was obtained instead.Parts of the data on Au–Ru and Ag–Pt systems have been published in Analytica Chimica Acta (2005, 537, 279–284) and Journal of Physical Chemistry B (2005, 109, 5468–5472), respectively.     

Scattering Efficiency and LSPR Tunability of Bimetallic Ag,Au, and Cu Nanoparticles

Scattering efficiencies of Ag–Cu, Ag–Au, and Au–Cu alloy nanoparticles are studied based on Mie theory for their possible applications in solar cells. The effect of size (radius), surrounding medium, and alloy composition on the scattering efficiency at the localized surface plasmon resonance (LSPR) wavelengths has been reported. In the alloy nanoparticles of Ag_1?x Cu _x , Au_1?x Cu _x and Ag_1?x Au _x ; the scattering efficiency gets red-shifted with increase in x. Moreover, the scattering efficiency enhancement can be tuned and controlled with both the alloy composition and the surrounding medium refractive index. A linear relationship which is in good agreement to the experimental observations between the scattering efficiency and metal composition in the alloys are found. The effect of nanoparticle size and LSPR wavelength (scattering peak position) on the full width half maxima and scattering efficiency has also been studied. Comparison of Au–Ag, Au–Cu, and Ag–Cu alloy nanoparticles with 50-nm radii shows the optical response of Ag–Cu alloy nanoparticle with wide bandwidth in the visible region of the electromagnetic spectrum making them suitable for plasmonic solar cells. Further, the comparison of Ag–Cu alloy and core@shell nanoparticles of similar size and surrounding medium shows that Cu@Ag nanoparticle exhibits high scattering efficiency with nearly the same bandwidth.     

Thermoluminescence of mercaptoethanol‐capped ZnS:Mn nanoparticles

The thermoluminescence (TL) of nanoparticles has become a matter of keen interest in recent times but is rarely reported. This article reports the synthesis of ZnS:Mn nanocrystals using a chemical route, with mercaptoethanol (ME) as the capping agent. The particle sizes for the nanocrystals were measured by X‐ray diffraction (XRD) and also by studying transmission electron microscopy (TEM) patterns. The particle sizes of the synthesized samples were found to be between 1 and 3 nm. For samples with different concentrations of the capping agent, it was found that the TL intensity of the ZnS:Mn nanoparticles increased as the particle size decreased. A shift in the peak position of the TL glow curve was also seen with decreasing particle size. The TL intensity was found to be maximal for samples with 1.2% of Mn. A change in the peak position was not found for samples with different concentrations of Mn. The half‐width glow peak curve method was used to determine the trap‐depth. The frequency factor of the synthesized samples was also calculated. The stability of the charge carriers in the traps increases with decreasing nanoparticle size. The higher stability may be attributed to the higher surface/volume ratio and also to the increase in the trap‐depth with decreasing particle size. Copyright © 2014 John Wiley & Sons, Ltd.