Tunable Photophysical Behavior of a Novel Fluorescent Probe by Silver/Gold and Core–Shell NPs

Plasmonics - The photophysical and photochemical behaviors of a novel fluorescent probe, namely 5-(4-(dimethylamino)phenyl)-1-(thiophen-2-yl)penta-2,4-dien-1-one (DMATP), were tuned by solvent...     

Comparison of Gold and Silver/Gold Bimetallic Surface for Highly Sensitive Near-infrared SPR Sensor at 1550 nm

A large majority of surface plasmon resonance (SPR) sensors reported in the literature are designed to operate in the visible electromagnetic spectrum. However, the near-infrared, particularly at the telecommunications wavelength of 1550 nm, is also especially attractive for SPR sensing applications. In fact, SPR sensors operating in this region benefit from narrower resonance and deeper field penetration. In this paper, we report a theoretical and experimental study of an SPR sensor operating at a fixed wavelength of 1550 nm. The influence of the choice of metals and the interrogation methods on the sensitivity of the resulting SPR sensor is investigated. Two types of sensor chips (simple gold (Au) and bimetallic silver/Au structure) and three interrogation methods (monitoring of the position of the reflectivity minimum, the position of the centroid, and the intensity evolution of the reflectivity) are examined. We show that a refractive index resolution of 2.7?×?10^?6 refractive index unit can be easily obtained, and with further optimization of the measurement system, the ultimate limit of detection is expected to be even lowered. Therefore, the approach discussed here already shows a promising potential for highly sensitive SPR sensors.     

A Visualized Assay for Quercetin Based on the Formation of Silver–Gold Alloy Nanoparticles

A visualized assay for quercetin (QU) was first developed based on the formation of silver–gold alloy nanoparticles in this contribution. With the ability to reduce metal ions to metal substances, QU could reduce Ag⁺ absorbed on the surface of gold nanoparticles to metallic silver. The thickness of the formed Ag shell and the color change of the solution were proportional to the concentration of QU. Therefore, visualized detection of QU could be realized by studying the surface resonance plasmon absorption spectra of the analytical systems after addition of different concentration of QU. Under optimum conditions, trace amount of QU could be detected in the linear range 9.0?×?10^?7–1.0?×?10^?4 mol L^?1 with a detection limit of 6.5?×?10^?7 mol L^?1. The present assay was applied in the determination of QU in human serum and satisfactory results were obtained. This assay is simple, rapid, and cost-effective, and it is a powerful complement for the spectroscopy assays for QU. Also, it is the first visualized spectroscopic assay of QU until now.     

Phase Transition and Optical Properties of DNA–Gold Nanoparticle Assemblies

We review recent work on DNA-linked gold nanoparticle assemblies. The synthesis, properties, and phase behavior of such DNA–gold nanoparticle assemblies are described. These nanoparticle assemblies have strong optical extinction in the ultraviolet and visible light regions; hence, the technique is used to study the kinetics and phase transitions of DNA–gold nanoparticle assemblies. The melting transition of DNA–gold nanoparticle assemblies shows unusual trends compared to those of free DNA. The phase transitions are influenced by many parameters, such as nanoparticle size, DNA sequence, DNA grafting density, DNA linker length, interparticle distance, base pairing defects, and disorders. The physics of the DNA–gold nanoparticle assemblies can be understood in terms of the phase behavior of complex fluids, with the colloidal gold interaction potential dominated by DNA hybridization energies.     

Observation of Size-Dependent Electron–Phonon Scattering and Temperature-Dependent Photoluminescence Quenching in Triangular-Shaped Silver Nanoparticles

Plasmonics - Research studies on plasmonic properties of triangular-shaped silver nanoparticles might lead to several interesting applications. However, in this work, triangular-shaped silver...     

Source–Sink Relations in the Organs and Tissues of Silver Birch during Different Scenarios of Xylogenesis

Russian Journal of Plant Physiology - Source–sink relations in the “leaf–stem–root” system at the time of cambial growth were studied in two forms of silver birch:...     

Plasmonic Circular Dichroism Study of DNA–Gold Nanoparticles Bioconjugates

Plasmonic circular dichroism (CD) responses of hybrid nanostructures containing noble metal nanoparticles and chiral molecules have received increasing interest with various applications in nanophotonics. Chiral biomolecules show strong CD signals typically found in the ultraviolet region, whereas, in the visible range, they produce a weak signal. Strengthening the CD signal in the visible region is of high importance, which could be achieved through fabrication of novel hybrid nanostructures. Herein, gold nanoparticles (GNPs) have been assembled via DNA linker to investigate the possibility of enhancing plasmonic CD signal in the visible range. DNA-linked assemblies with pre- and postannealed conditions were characterized by ultraviolet–visible spectroscopy, dynamic light scattering (DLS), and CD spectropolarimetry. In the presence of DNA linker with sticky ends, the aggregation phenomenon was traced by red shifts of surface plasmon resonance of nanoparticles. Time-dependent hybridization of single-stranded “sticky ends” with DNA-conjugated GNPs and increased probability of hydrogen bond formation lead to enhancement of CD signals in the ultraviolet region. Complexation of biomolecule and nanoparticle assemblies induced enhanced CD signals in the visible range, which was noticed both before and after purification. DLS characterization of the assemblies also confirmed the difference in the size of aggregates, which could be controlled by the linker molecules. This investigation encourages possibility of utilizing plasmonic CD technique as a tool for tracing fabricated nanostructure assemblies with enhanced characterization possibility.     

Multiple Surface Plasmon Resonances in a Metal–Insulator–Metal Structure Assembled Via Silver–Copper Nanoparticle Arrays

The Ag–Cu nanoparticle arrays, prepared using the electrochemical deposition method, were assembled into the metal–insulator–metal (MIM) structure with polyvinyl alcohol acting as insulating layer, the transmission spectrum of the MIM structure was observed to support the multiple surface plasmon resonances in the wavelength range 1,000 to 2,600 nm. The multiple peaks were formed due to the superposition and coupling of the surface plasmon resonance of nanoparticles with various sizes in the metal layers. The newly found MIM structure in which multiple resonances exist has a potential application in multiband-pass filters and optical magnetic metamaterials at the resonance wavelength.     

Can Infants Tell the Difference between Gold and Yellow?

There is a large literature focused on the color perception of matte surface. However, recent research showed that the component of surface specular reflection, such as glossiness, also affects categorical color perception. For instance, the color term “gold” was used to name high specular stimuli within a specific range of chromaticity, which overlaps with those of yellow and orange for low specular stimuli. In the present study, we investigated whether the component of surface specular reflectance affects the color perception of 5- to 8-month-old infants by using the preferential looking technique. In the first experiment, we conducted a simple test to determine whether infants perceive yellow and gold as the same color by comparing their preference for these colors over green. If the infants perceive yellow and gold as the same color, they would show similar preference scores over green. On the other hand, if infants show different preference scores over green, it indicates that infants do not perceive yellow and gold as the same color. Only the 7–8 month-old infants showed different preference scores for gold and yellow over green. This result indicates that the 7–8 month-old infants perceive gold and yellow as different colors. In Experiment 2, we eliminated the component of specular reflectance on the gold surface and presented it against green to infants. A similar preference score of yellow over green was obtained. This result suggests that the difference between the preference scores for gold and yellow over green in Experiment 1 was based on representations of glossiness.     

Studying Protein–DNA Complexes Using Gold Nanoparticles by Exploiting Particle Aggregation,Refractive Index Change,and Fluorescence Quenching and Enhancement Principles

Plasmonics - Gold nanoparticles (AuNPs) have a unique optical phenomena termed localized surface plasmon resonance that is determined by particle shape, size, interparticle distance (or aggregation...     

Bismuth and Silver in Cosmetic Products: A Source of Environmental and Resource Concern?

Bismuth (Bi) and silver (Ag) are used in increasing amounts and are consequently being emitted from various sources and showing high accumulation rates in soils when sewage sludge is applied on arable land. This study aimed to analyze the amounts of Bi and Ag in three cosmetic products (foundation, powder, and eye shadow) in order to study the flows in urban wastewater in Stockholm, Sweden. Analyses showed that Bi was present in very high concentrations (7,000 to 360,000 milligrams per kilogram) in one third of the analyzed foundation and powder samples, whereas Ag concentrations all were below the detection limit. These cosmetic products explained approximately 24% of the measured total Bi amounts per year reaching the WWTP (wastewater treatment plant), making cosmetics a major Bi source, whereas for Ag the corresponding contribution was <0.1% of the measured annual Ag amounts. The results were roughly adapted for Europe and the United States, estimating the Bi flows from cosmetics to WWTPs. On a global scale, these flows correspond to a non‐negligible part of the world Bi production that, every year, ends up in sewage sludge, limiting the reuse of a valuable metal resource. From an environmental and resource perspective, foundations and powder products should be considered as significant sources of measured Bi amounts in sludge. This large Bi flow must be considered as unsustainable. For Ag, however, the three analyzed cosmetic products are not a significant source of the total Ag load to WWTPs.     

Frequency-Dependent Polarization Properties of Local Electric Field in Gold–Dielectric Multi-Nanoshells

The polarization properties of the local electric field in the gold–dielectric–gold multilayer nanoshells are investigated by theoretical calculation based on the quasi-static approximation. The calculation results show that the complete polarized incident light does not only stimulate the same directional polarized local electric field. The polarized angle of the local field may changes from 0° to 90° as the wavelength and location are changed. The distributions of local field polarization are different in dielectric layer or gold shell and display different features in different plasmonic hybridization mode. As the incident wavelength is increased, the hot spot of polarizing angle moves monotonously in the middle dielectric shell, whereas moves nonmonotonously in the gold shell and surrounding environment. In the gold shell, the gap between hot spots of polarizing angle may occur at the resonance frequency. However, the hot spots of polarizing angle always occur at the resonance frequencies in the surrounding environment. These interesting results show that the single-molecule detection based on metal nanostructure induced surface-enhanced Raman scattering and surface enhanced fluorescence could be optimized by adjusting the incident light polarization and frequency.     

Enhanced Nonlinear Optical Response of Resonantly Coupled Silver Nanoparticle–Organic Dye Complexes

The influence of metal nanoparticles on linear and nonlinear optical properties of surrounding organic molecules has been widely investigated, whereas much less attention has been paid to the influence of molecules on properties of nanoparticles. Here, we employ transient absorption spectroscopy to address the nonlinear optical responses of the resonantly coupled silver nanoparticle–organic dye systems and demonstrate that silver nanoparticles covered with dye molecules show enhanced and spectrally different nonlinear extinction changes from pristine nanoparticles. We identify changes of the plasmon resonance band of nanoparticles induced by excitation of surrounding dye. We attribute these exciton–plasmon coupling effects to the excitation-induced refractive index modifications of the dye layer surrounding a nanoparticle and to the back-transfer of the oscillator strength borrowed by the dye from the nanoparticle.     

The Postnatal Development of the Cerebellum— A fMRI and Silver Study

Summary The aim of this study was to evaluate the postnatal development of the cerebella of the pig and to compare this with the activation of the fMRI. The cells in the cerebella were studied by silver technique and the activation of the fMRI in the cerebella was initiated by flexion and extension of the hind paw. Our results showed an increase of the branching of the cells of the cerebellar cortex postnatally, coordinated with registration of fMRI active sites in the cerebella at 6-month postnatal. We concluded that the full maturation of the cerebella was around 6-month postnatal in the pig.     

Electron Energy Loss and One- and Two-Photon Excited SERS Probing of “Hot” Plasmonic Silver Nanoaggregates

We report electron energy loss spectroscopy (EELS) and one- and two-photon excited surface-enhanced Raman scattering (SERS) and hyper Raman studies on plasmonic silver nanoaggregates. By comparison with computations, EELS imaging reveals an inverse relationship between local field intensity in an optical experiment and electron energy loss intensity at energies corresponding to excitation wavelengths used for optical probing. This inverse relation exists independent on specific nanoaggregate geometries and is mainly controlled by the gap size between the particles forming the aggregate. The ratio between two- and one-photon excited SERS measured at different excitation wavelengths provides information about local fields in the hottest spots and their dependence on the photon energy. Our data verify experimentally the predicted increase of local optical fields in the hot spots with increasing wave lengths. The reported findings show new experimental ways to characterize local fields of plasmonic nanostructures. This is of particular importance for complex structures which are not easily approachable by computations.     

Broadband Solar Absorption Enhancement in a Silver–Epoxy Nanocomposite for Use as Selective Coating

Plasmonics - This paper reports the optical properties of a black silver–epoxy nanocomposite deposited on copper substrate for use as selective solar absorber. The silver nanoparticles at...     

Bioaccumulation of Gold by Filamentous Cyanobacteria Between 25 and 200°C

Plectonema boryanum UTEX 485 was reacted with aqueous AuCl ₄ ^? solutions ( ～ 2 mM Au) at 25 to 100°C for 1 month, and 200°C for one day. Addition of AuCl₄ ^? to cyanobacteria killed the cultures instantly, and Au was precipitated throughout the cells as nanoparticles. Precipitation of octahedral crystal platelets of Au occurred in the aqueous fluid, with particle size increasing with increase in temperature from about 1.5 μ m at 25°C to 10 μ m at 100°C. Addition of AuCl₄ ^? to suspensions of the dead, autoclaved cyanobacteria also precipitated Au from solution, suggesting that the presence of cell degradation products caused instability of AuCl₄ ^? .