Oligonucleotide-Mediated Au–Ag Core–Shell Nanoparticles

The bimetallic core–shell nanoparticles show unique plasmonic properties and their preparations and characterizations are currently under investigation. A new type of Au core–Ag shell (Au@Ag) nanoparticles is prepared by sandwiching the chemically attached Raman reporter molecules (RRMs) and a 12-base-long oligonucleotide between the 13 nm average size core-gold nanoparticles (AuNPs) and 9 nm and 21 nm average size of Ag shell. The synthesized Au@Ag nanoparticles are tested for their surface-enhanced Raman scattering (SERS) performance. It is found that the chemical attachment of the oligonucleotides along with the RRM improved the enhancement in Raman scattering more than one order of the magnitude with the Au@Ag nanoparticles with an average 9-nm shell thickness while the Au@Ag nanoparticles with 21 nm average shell thickness have poor SERS activity. A minimum enhancement factor of 1.0 × 10⁷ is estimated for the SERS active oligonucleotide-mediated Au@Ag nanoparticles. The approach may provide new routes for preparation of highly sensitive new generation of bimetallic core–shell nanoparticles.     

Thermodynamic and structural properties of the specific binding between Ag ion and C:C mismatched base pair in duplex DNA to form C–Ag–C metal-mediated base pair

Metal ion-nucleic acid interactions have attracted considerable interest for their involvement in structure formation and catalytic activity of nucleic acids. Although interactions between metal ion and mismatched base pair duplex are important to understand mechanism of gene mutations related to heavy metal ions, they have not been well-characterized. We recently found that the Ag⁺ ion stabilized a C:C mismatched base pair duplex DNA. A C–Ag–C metal-mediated base pair was supposed to be formed by the binding between the Ag⁺ ion and the C:C mismatched base pair to stabilize the duplex. Here, we examined specificity, thermodynamics and structure of possible C–Ag–C metal-mediated base pair. UV melting indicated that only the duplex with the C:C mismatched base pair, and not of the duplexes with the perfectly matched and other mismatched base pairs, was specifically stabilized on adding the Ag⁺ ion. Isothermal titration calorimetry demonstrated that the Ag⁺ ion specifically bound with the C:C base pair at 1:1 molar ratio with a binding constant of 10⁶ M⁻¹, which was significantly larger than those for nonspecific metal ion-DNA interactions. Electrospray ionization mass spectrometry also supported the specific 1:1 binding between the Ag⁺ ion and the C:C base pair. Circular dichroism spectroscopy and NMR revealed that the Ag⁺ ion may bind with the N3 positions of the C:C base pair without distorting the higher-order structure of the duplex. We conclude that the specific formation of C–Ag–C base pair with large binding affinity would provide a binding mode of metal ion-DNA interactions, similar to that of the previously reported T-Hg-T base pair. The C–Ag–C base pair may be useful not only for understanding of molecular mechanism of gene mutations related to heavy metal ions but also for wide variety of potential applications of metal-mediated base pairs in various fields, such as material, life and environmental sciences.     

A Highly Sensitive Resonance Scattering Assay for Immunoglobulin M Using Ag(I)–Hydroquinone–Immunonanogold Catalytic Reaction

Ten-nanometer nanogold showed the strongest catalytic effect on the particle reaction between Ag(I) and hydroquinone to form nanosilver particles that exhibited the strongest resonance scattering (RS) peak at 350 nm. The enhanced RS intensity was linear to the nanogold concentration in the range of 30–5,700 nM Au. The nanogold was used to label goat antihuman immunoglobulin M (GIgM) to obtain an immunonanogold probe (AuGIgM) for immunoglobulin M (IgM). Based on the nanogold-labeled immunoreaction between IgM and AuGIgM, centrifugation, and AuGIgM–Ag(I)–hydroquinone nanocatalytic reaction, a highly sensitive and selective immunonanogold-catalytic Ag particle RS assay for 0.2–300 ng mL^?1 IgM was proposed, with a detection limit of 0.1 ng mL^?1. This assay was simple and sensitive and was applied to assay IgM in serum samples, with satisfactory results.     

Unravelling the interface of Co–Pi/Ag/Fe2O3 and Ni–Pi/Ag/Fe2O3 heterostructures for enhanced solar water splitting

Recently, a new type of haematite-based (a-Fe₂O₃) photoanode has achieved a considerable catalytic performance through simply depositing Ag and cobalt phosphate (Co–Pi) nanoparticles (NPs) onto haematite nanosheets. However, there is no detailed mechanism study on the reason for high-performance catalysis. In view of this, we conduct first-principles calculations and our results indicate that there is a further accumulation of positive charge on Ag NPs on the heterogeneous interfaces with the addition of Co–Pi NPs than that of haematite modified only by Ag NPs. Also, there is a slight increase of the adsorption energy of water molecules.     

Near-infrared Plasmonic Far-field Nanofocusing Effects with Elongated Depth of Focus based on Hybrid Au–Dielectric–Ag Subwavelength Structures

In this paper, we propose a new far-field nanofocusing lens with elongated depth of focus (DOF) under near-infrared (NIR) wavelength. The surface plasmons can be excited by using the hybrid metal–insulator–metal (MIM) subwavelength structure under the NIR wavelength. The constructive interference of surface plasmons launched by the subwavelength MIM structure can form a nanoscale focus that is modulated by the novel metal grating from the near field to the far field. The numerical simulations demonstrated that a nanoscale focal spot (in plane focal area 0.177λ ²) with elongated DOF (3.358λ) and long focal length (5.084λ) can be realized with reasonably designing parameters of the lens. By controlling the positions of the inner radii of each slit ring and the grating width, the focal length, focal spot, and DOF can be tuned easily. This design method, which can obtain the nanoscale focal spot and micron DOF in far field under NIR illumination, paved the road for utilizing the NIR plasmonic lens in superresolution optical microscopic imaging, optical trapping, biosensing, and complex wavefront/beam shaper.     

Silver Fused Conducting Fiber Formation of Au–Ag Core-Shell Nanoparticles Mediated by Ascorbic Acid

In this paper, we report the spontaneous formation of fibrous structures consisting of assemblies of Au–Ag core-shell nanoparticles (NPs) from a solution consisting of Au–Ag core-shell NPs and l-ascorbic acid (AA). AA acted both as the reducing agent for the generation of NPs and also as the mediator for the formation of fibers. The process of fiber formation involved three steps—reduction of HAuCl₄ to Au NPs by AA, subsequent formation of Au–Ag core-shell NPs after addition of AgNO₃, and spontaneous formation of fibers from the mixtures in water. It took typically about 30 days to form complete fibers that are of lengths of several hundred micrometers to millimeters, although nanofibers started forming from the first day of solution preparation. The width of each of these fibers was typically about 1–4 μm with length of each segment of fiber bundle, on the order of 40 μm. Formation of fibers was also observed in absence of AgNO₃. These fibers consisted of Au NPs and polymer of AA degradation products and were not electrically conducting. Also, low concentrations of AgNO₃ produced fibers with low electrical conductivity. However, it was observed that increase in the amount of AgNO₃ leads to the formation of fibers that were electrically conducting with conductivity values in the range of metallic conductivity. Spectroscopic and electron microscopic investigations were carried out to establish the formation of fibers. The details of fiber formation mechanism under different conditions and electrical conductivities of the fibers are discussed in the article.     

Vapor Phase Deposition, Structure, and Plasmonic Properties of Polymer-Based Composites Containing Ag–Cu Bimetallic Nanoparticles

Nanocomposite (NC) thin films with noble metal nanoparticles embedded in a dielectric material show very attractive plasmonic properties due to dielectric and quantum confinement effects. For single component nanoparticles (NPs), the plasmon resonance frequency can only be tuned in a narrow range. Much interest aroused in bimetallic nanoparticles (BNPs), however many wet chemical approaches do not allow large variation of the NP alloy composition and filling factor. Here, we report a vapor phase co-deposition method to produce polymer–metal NCs with embedded Ag_1 − x Cu _x alloy particles. The method allows production of NPs with controlled alloy composition (x), metal filling (f) and nanostructure in a protecting Teflon AF matrix. The nanostructure size and shape were characterized by transmission electron microscope. Energy dispersive X-ray spectroscopy was used to determine x and f. The optical properties and the position of surface plasmon resonances were studied by UV–Vis spectroscopy. The plasmon resonances can be tuned over a large range of the visible spectrum associated with the change in x, f, and nanostructure. For low filling factors and small particle sizes, only one resonance peak was observed. This is attributed to enhanced miscibility at the nanoscale. Double plasmon resonances were seen for larger particle sizes in accord with phase separation expected from the bulk phase diagram and were explained in terms of the formation of core-shell structures with Cu core and Ag shell. Changes upon annealing at 200 °C are also reported.     

Karyotype and chromosomal characteristics of Ag–NOR sites and 5S rDNA in European smelt, Osmerus eperlanus

Karyotype and cytogenetic characteristics of European smelt Osmerus eperlanus were investigated using different staining techniques (sequential Ag-, CMA3 and DAPI banding) and PRINS to detect 5S rDNA and telomeric sites. The diploid chromosome number was invariably 2n = 56 and karyotype composed of 5 pairs of metacentrics, 9 pairs of subtelocentrics and 14 pairs of subtelo- to acrocentrics. The DAPI-positive heterochromatic regions were found in centromeric positions on bi-armed chromosomes and few acrocentrics. Additionally, some interstitial DAPI-positive bands were identified on three pairs of submetacentric chromosomes. The nucleolar organizer regions (NORs) were detected in the short (p) arms of the largest metacentric pair of chromosomes No. 1. Sequential banding (Giemsa-, AgNO₃ and CMA₃ stainings) revealed NOR sites corresponding to achromatic regions but not associated with CMA₃-positive blocks of heterochromatin located on either side of NORs. Individuals from the analyzed population had this conspicuous pair of chromosomes always in heterozygous combination. A complex inversion system was hypothesized to be involved in the origin of the observed variation but analysis with telomeric PRINS and PNA-FISH did not reveal any Interstitial Telomeric Sites (ITS). Hybridization signals were confined exclusively to terminal chromosomal regions. The 5S ribosomal sites as revealed by PRINS were found to be invariably located in the short (p) arms of four pairs of subtelocentric chromosomes. Cytotaxonomic comparisons of the present results with the voluminous available cytogenetic data-set from salmoniform and esociformes fishes appear to support the recent view, based on robust molecular-based phylogeny, that salmoniform and osmeriform fishes are not as closely related as previously assumed.     

Calculation of the Three-Dimensional Structures of Two Antigenic Sequences, Pro–Pro–Pro–Pro–Asn–Pro–Asn–Asp–Pro and Pro–Pro–Pro–Pro–Asn–Pro–Asn–Asp–Pro–Pro–Pro, of the Circumsporozoite Protein From a Malaria-Causing Plasmodium

Using the chain build-up procedure based on the program ECEPP, we have computed the lowest energy structures for two terminally blocked subsequences from the antigenic circumsporozoite protein of Plasmodium berghei, that is known to cause malaria in animals. The full antigenic sequence is an octapeptide proline-rich tandem repeat, (Pro–Pro–Pro–Pro–Asn–Pro–Asn–Asp)₂. We computed the structures for the first octapeptide plus one Pro from the second octapeptide, terminally blocked CH₃CO–Pro–Pro–Pro–Pro–Asn–Pro–Asn–Asp–Pro–NHCH₃ as well as the first octpeptide with an additional three Pro residues from the adjoining unit, i.e., CH₃CO–Pro–Pro–Pro–Pro–Asn–Pro–Asn–Asp–Pro–Pro–Pro–NHCH₃. We find that the first sequence adopts a number of different low energy structures, the most probable of which has a probability of occurrence of 56 %. Addition of two more Pro residues results in the adoption a single, unique lowest energy structure that has a probability of occurrence of over 95 % without solvation effects and 86 % when solvation effects are included in the calculations. We predict that this structure may be the one recognized as a major antigenic determinant.     

Is Ag(I) an adequate probe for Cu(I) in structural copper–metallothionein studies?

The binding abilities of silver(I) to mammalian MT 1 have been studied and compared with those of copper(I), recently reported [Bofill et al. (2001) J Biol Inorg Chem 6:408–417], with the aim of analyzing the suitability of Ag(I) as a Cu(I) probe in Cu–MT studies. The Zn/Ag replacement in recombinant mouse Zn₇–MT 1 and corresponding Zn₄-MT 1 and Zn₃-MT 1 fragments, as well as the stepwise incorporation of Ag(I) to the corresponding apo-MTs, have been followed in parallel by various spectroscopic techniques including electronic absorption (UV–vis), circular dichroism (CD) and electrospray mass spectrometry coupled to capillary zone electrophoresis (CZE-ESI-MS). A comparative analysis of the sets of data obtained in the titration of Zn₇–MT 1, Zn₄–MT 1 and Zn₃-MT 1 with AgClO₄ at pH 7.5 and 2.5 has led to the reaction pathways followed during the incorporation of silver to these proteins under these specific conditions, disclosing unprecedented stoichiometries and structural features for the species formed. Thus, the Zn/Ag replacement in Zn₇–MT 1 at pH 7.5 has revealed the subsequent formation of Ag₄Zn₅–MT, Ag₇Zn₃–MT, Ag₈Zn₃–MT, Ag₁₀Zn₂–MT, Ag₁₂Zn₁–MT, Ag_x–MT, x=14–19, whose structure consists of two additive domains only if Zn(II) remains coordinated to the protein. A second structural role for Zn(II) has been deduced from the different folding found for the Ag_x–MT species of the same stoichiometry formed at pH 7.5 or 2.5. Comparison of the binding features of Cu(I) and Ag(I) to the entire MT at pH 7.5 shows that, among all the _xZn_y–MT (0y<7) species found, only M^I₄Zn₅–MT [(Zn₄)(₄Zn₁)] and M^I₇Zn₃–MT [(₃Zn₂)(₄Zn₁)], which form during the first stages of the Zn(II)/M(I) metal replacement, show comparable 3D structures; thus, they are the only species where Ag(I) ions can be predicted to be an adequate probe for Cu(I).Electronic Supplementary Material Supplementary material is available in the online version of this article at .     

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

Continuous monitoring of air quality and rapid detection of pollutants are highly desirable in urban planning and development of smart cities. One of the primary greenhouse gases responsible for environmental degradation and respiratory diseases is nitrogen dioxide (NO₂). Existing gas sensors for measuring NO₂ concentration suffer from drawbacks such as cross-sensitivity, limited range, and short life span. On the other hand, optical sensors, in particular, surface plasmon resonance (SPR) sensors, have emerged as a preferred alternative owing to advantages like high selectivity, immunity to electromagnetic interference, and low response time. In this work, we design and simulate a NO₂ sensor based on a glass waveguide coated with a gold film. Surface plasmons are excited at the interface by a 400–500-nm light source, incident at an angle of 43.16°. To enhance the sensitivity, we further coat the waveguide with three layers of carbon-silver (C–Ag) nanodots, which increases the surface plasmon field amplitude by nearly 7 times, in the absence of NO₂. When NO₂ concentration is varied in the range of 0–200 ppm, a corresponding change is observed in the reflected amplitude. In the absence of the C–Ag nanodots layer, the sensitivity is only 0.00042%/ppm, and on addition of C–Ag nanodots, the sensitivity increases significantly to 0.14235%/ppm which is nearly 343 times higher. These results demonstrate the efficiency of implementing nanodots in SPR sensor to detect and trace concentrations of contaminants in the gas phase.

     

发酵支原体M161Ag的研究进展

发酵支原体是一类没有细胞壁的原核细胞型微生物。作为艾滋病的协同刺激因子,其作用机制至今未明,近年来研究发现发酵支原体的膜表面有一种膜脂蛋白抗原物质,称M161Ag,它可激活单核/巨噬细胞系统的细胞,从而释放多种促炎性细胞因子,如白细胞介素1β,肿瘤坏死因子α,白细胞介素6,10,12,一氧化氮;还可通过旁路途径激活补体系统,致宿主细胞产生炎症反应和天然免疫,另外,M161Ag还促使未成熟的树突细胞成熟,通过树突细胞的抗原呈递作用,介导宿主细胞的特异性免疫应答。本文重点介绍M161Ag的功能及其与配体相互作用的信号传递途径。     

Real-time kinetic analysis of hCG–monoclonal antibody interaction using radiolabeled hCG probe: presence of two forms of Ag–mAb complex as revealed by solid phase dissociation studies

Real-time kinetics of ligand–ligate interaction has predominantly been studied by either fluorescence or surface plasmon resonance based methods. Almost all such studies are based on association between the ligand and the ligate. This paper reports our analysis of dissociation data of monoclonal antibody-antigen (hCG) system using radio-iodinated hCG as a probe and nitrocellulose as a solid support to immobilize mAb. The data was analyzed quantitatively for a one-step and a two-step model. The data fits well into the two-step model. We also found that a fraction of what is bound is non-dissociable (tight-binding portion (TBP)). The TBP was neither an artifact of immobilization nor does it interfere with analysis. It was present when the reaction was carried out in homogeneous solution in liquid phase. The rate constants obtained from the two methods were comparable. The work reported here shows that real-time kinetics of other ligand–ligate interaction can be studied using nitrocellulose as a solid support.     

Nanosecond Laser–Assisted Tuning of the Plasmon Band of Triangular-Shaped Ag Nanostructures and Development of a Broadband Visible-Near Infrared Light Absorber

Plasmonics - Most of the outstanding applications of silver nanoparticles (Ag NPs) have arisen from their tunable localized surface plasmon resonance (LSPR). In this report, we have systematically...     

黄鳝染色体Ag—NORS多态性的研究

采用PHA活体处理直接制片,对黄鳝染色体进行Giemsa染色、C-带及Ag-NORs等相继系列研究。结果发现,黄鳝的染色体Ag-NORs具有明显的个体特异性的数目多态、分布多态和形态多态现象。11尾被检测个体中,多态特征可分为4种类型。位于第3或第7号染色体臂内的次缢痕是Ag-NORs所在的区域,该区域分布有大量的结构异染色质,即Ag-NORs与C-带强阳性呈现严格的同步对应。本文根据实验结果,对黄鳝AS-NORs多态性的发生机制及其与结构异染色质的关系进行了探讨。     

Nonorthogonal tight-binding model with H–C–N–O parameterisation

A parametric nonorthogonal tight-binding model (NTBM1) with the set of parameters for H–C–N–O systems is presented. This model compares well with widely used semi-empirical AM1 and PM3/PM7 models but contains less fitting parameters per atom. All NTBM1 parameters are derived based on a criterion of the best agreement between the calculated and experimental values of bond lengths, valence angles and binding energies for various H–C–N–O molecules. Results for more than 200 chemical compounds are reported. Parameters are currently available for hydrogen, carbon, nitrogen, oxygen atoms and corresponding interatomic interactions. The model has a good transferability and can be used for both relaxation of large molecular systems (e.g., high-molecular compounds or covalent cluster complexes) and long-timescale molecular dynamics simulation (e.g., modelling of thermal decomposition processes). The program package based on this model is available for download at no cost from http://ntbm.info.     

Thermal conductivity of ferromagnetic metallic La0.95Ag0.05MnO3 manganites: role of carrier,spin waves and lattice–impurity scattering

The lattice contribution to the thermal conductivity (κ_ph) of La_0.95Ag_0.05MnO₃ manganites is theoretically analysed within the framework of Kubo model. The theory is formulated when thermal conduction is limited by the scattering of phonons from defects, grain boundaries, charge carriers, spin waves and phonons. The lattice thermal conductivity dominates in Ag-doped manganites and is artefact of strong phonon–impurity and phonon–phonon scattering mechanism in the ferromagnetic metallic state. The electronic contribution to the thermal conductivity (κ_e) is estimated following the Wiedemann–Franz law. Another important contribution in the metallic phase should come from spin waves (κ_m). It is noticed that κ_m increases with a T² dependence on the temperature. The behaviour of the thermal conductivity in manganites is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron, magnon and phonon contributions.     

Ag—43型高铜白合金精通过技术鉴定

上海齿科材料厂经多年探索并在各方的协助配合下,按照国际标准牙科汞用合金ISO、1599—1986(E)研制成Ag—43型高铜白合金精,其与常规白合金精的不同点是铜含量超过6％,(国际上统称为高铜产品),凝固后的膨胀系数为6～7μm/cm,同常规白合金精一样,能与牙本质密切结合,不会产生微隙漏,不会导致继发龋,既节银又实用,实为一种良好的永久性补牙材料。经全国17个省的27个市、2个县的医疗单位临床试用后,专家们一致认为该产品具有