Silver-coated zeolite crystal films as surface-enhanced Raman scattering substrates

Silver-coated zeolite A and zeolite NaX crystal films prepared by vacuum deposition were investigated as surface-enhanced Raman scattering (SERS) substrates. The substrates were active for the enhancement of Raman scattering from uranyl ions. A detection limit of 10(-5) M for uranyl was obtained using silver-coated zeolite A films. One advantage of these zeolite-based substrates is that the negatively charged microporous framework provides the selectivity for adsorption based on static electric charges. The SERS effects of positively charged uranyl ions and neutrally charged benzoic acid were compared. For the zeolite A substrate, there was a 100-times-greater sensitivity.     

Surface-enhanced Raman spectroscopy using silver-coated porous glass-ceramic substrates

Surface-enhanced Raman scattering (SERS) has been studied using a silver-coated porous glass-ceramic material as a new type of substrate. The porous glass-ceramic is in the CaO-TiO2-P2O5 system prepared by controlled crystallization and subsequent chemical leaching of the dense glass-ceramic, leaving a solid skeleton with pores ranging in size from 50 nm to submicrometer. Silver was coated on the surface of the porous glass-ceramic by radio frequency (RF) sputtering or e-beam evaporation in vacuum. SERS spectra of excellent quality were obtained from several dyes and carboxylic acid molecules, including rhodamine 6G, crystal violet, isonicotinic acid, and benzoic acid, using this new substrate. This new substrate showed a good compatibility with these molecules. The porous glass ceramic with a nanometer-structured surface accommodated both test molecules and silver film. The absorbed molecules were therefore better interfaced with silver for surface-enhanced Raman scattering.     

C18-modified metal-colloid substrates for surface-enhanced Raman detection of trace-level polycyclic aromatic hydrocarbons in aqueous solution

Metal colloids immobilized on a glass support substrate are modified with a self-assembled alkylsilane (C18) layer to promote adsorption of polycyclic aromatic hydrocarbons from aqueous solutions. Detection of these compounds from low concentration solutions is accomplished by using surface-enhanced Raman scattering (SERS). SERS spectra of pyrene adsorbed to C18-modified immobilized silver colloids are dominated by Raman bands that are not consistent with pyrene and indicate that pyrene undergoes a chemical reaction at the surface. The origins of this surface product are investigated, and it is determined that silver and oxygen are required to form the product, whose Raman spectrum is consistent with oxidation to a quinone. When a C18-modified gold-colloid substrate is used, Raman scattering consistent with unreacted pyrene is observed. The adsorption and detection of pyrene adsorbed from low (2 ppb) concentration aqueous solutions onto C18-modified gold-colloid substrates is reported; naphthalene and phenanthrene are detected at approximately 5 ppb. Adsorption kinetics are rapid (<5 min), and the concentration-dependent SERS response is consistent with a Langmuir isotherm.     

High-density silver nanoparticle film with temperature-controllable interparticle spacing for a tunable surface enhanced Raman scattering substrate

The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates. The high-density nanoparticle thin film is accomplished by self-assembling through the Langmuir-Blodgett (LB) technique on a water surface and transferring the particle monolayer to a temperature-responsive polymer membrane. The temperature-responsive polymer membrane allows producing a dynamic surface enhanced Raman scattering substrate. The plasmon peak of the silver nanoparticle film red shifts up to 110 nm with increasing temperature. The high-density particle film serves as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), and the scattering signal enhancement factor can be dynamically tuned by the thermally activated SERS substrate. The SERS spectra of Rhodamine 6G on a high-density silver particle film at various temperatures is characterized to demonstrate the tunable plasmon coupling between high-density nanoparticles.     

Preparation of silver nanoparticles dispersed in polyacrylonitrile nanofiber film spun by electrospinning

Ag nanoparticles dispersed in polyacrylonitrile (PAN) nanofiber film spun by electrospinning were in situ prepared by reduction of silver ions in N₂H₅OH aqueous solution. The Ag/PAN nanocomposite film was characterized by UV absorption spectroscopy, transmission electron microscopy (TEM) and surface-enhanced Raman scattering (SERS) spectroscopy. UV spectrum and TEM image show that silver nanoparticles with average diameter of 10 nm were obtained and dispersed homogeneously in PAN nanofibers. SERS spectrum indicates that the structure of PAN has been changed after Ag nanoparticles are dispersed in PAN.     

A novel method for fabricating the surface-enhanced Raman scattering substrates and its enhanced properties

We have got large area surface-enhanced Raman scattering (SERS) substrates with uniform high enhancement factors by the so-called moulage method for the first time. A silver film (99.99%) with several millimeters thickness was thermally evaporated on the porous anodic alumina templates and the SERS substrate was got after moving off the templates. Surface-enhanced Raman scattering spectra of pyridine (0.01 Mol/L) were measured under 632.8 nm excitation. The experimental enhancement factors were more than 10(5) and S/N(p-p) around 100 was obtained. We have compared the SERS spectra of pyridine collected from different locations on the same SERS substrate and different substrates, which illustrate the well uniform enhance properties and the reproducibility of this method, respectively. The comparison of the SERS spectra, obtained from the SERS substrates and Ag film evaporated directly on glass slide, have proved that the electromagnetic coupling between two adjacent nanoparticles was important to the SERS effect. We also used rhodamine 6G as the probe molecules and found that the different molecules were very sensitive to the morphology of the SERS substrates.     

Silver-coated dye-embedded silica beads: a core material of dual tagging sensors based on fluorescence and Raman scattering

We have developed a new type of dual-tag sensor for immunoassays, operating via both fluorescence and surface-enhanced Raman scattering (SERS). A one-shot fluorescence image over the whole specimen allows us to save considerable time because any unnecessary time-consuming SERS measurements can be avoided from the signature of the fluorescence. Dye-embedded silica beads are prepared initially, and then SERS-active silver is coated onto them via a very simple electroless-plating method. The Raman markers are subsequently assembled onto the Ag-coated silica beads, after which they are stabilized by silanization via a biomimetic process in which a poly(allylamine hydrochloride) layer formed on the Raman markers by a layer-by-layer deposition method acting as a scaffold for guiding silicification. In the final stage, specific antibodies are attached to the silica surface in order to detect target antigens. The fluorescence signal of the embedded dye can be used as a fast readout system of molecular recognition, whereas the SERS signals are subsequently used as the signature of specific molecular interactions. In this way, the antibody-grafted particles were found to recognize antigens down to 1 × 10(-10) g mL(-1) solely by the SERS peaks of the Raman markers.     

Controlled layer-by-layer formation of ultrathin TiO2 on silver island films via a surface sol-gel method for surface-enhanced Raman scattering measurement

A surface sol-gel process has been demonstrated to be an effective method for the surface modification of silver island films as unique SERS substrates for monitoring molecular adsorption on a dielectric titania surface. This layer-by-layer approach allows control of the thickness of the dielectric surface with a monolayer precision on silver surfaces. The enhancement of Raman scattering from adsorbed Rhodamine 6G molecules is inversely proportional to the thickness of the titania film, which is consistent with the decay of electromagnetic enhancement. Despite a reduction in the sensitivity of the film, a substantial improvement in the film was achieved as a result of the enhanced stability of this substrate compared to the silver island film without a TiO(2) coating.     

Silver nanowire layer-by-layer films as substrates for surface-enhanced Raman scattering

In this paper, the fabrication of highly stable, surface-enhanced Raman scattering (SERS) active dendrimer/silver nanowire layer-by-layer (LBL) films is reported. Ag nanowires, approximately 100 nm in diameter, were produced in solution and transferred, using the LBL technique, onto a single fifth-generation DAB-Am dendrimer layer on a glass substrate. The Ag nanowires, and the resulting LBL films were characterized using UV-visible surface plasmon absorbance, while the LBL films were further characterized by atomic force microscopy measurements and surface-enhanced Raman and resonance Raman scattering of several analytes. The dendrimer was found to effectively immobilize the Ag nanowires with increased control over spacing and aggregation of the particles. These films are shown to be excellent substrates for SERS/SERRS measurements, demonstrating significant enhancement, and trace detection capability. Several trial analytes were tested using a variety of excitation energies, and results confirmed effective enhancement of Raman signals throughout the visible range (442-785 nm) with different molecules. Analytes were deposited onto the enhancing Ag nanowire LBL films surface using both casting and Langmuir-Blodgett monolayer transferring techniques.     

Identification of organic materials in historic oil paintings using correlated extractionless surface-enhanced Raman scattering and fluorescence microscopy

A novel spectroscopic approach, correlated surface-enhanced Raman scattering (SERS) and fluorescence microscopy, is used to identify organic materials in two 18th century oil paintings. The vibrational fingerprint of analyte molecules is revealed using SERS, and corresponding fluorescence measurements provide a probe of local environment as well as an inherent capability to verify material identification. Correlated SERS and fluorescence measurements are performed directly on single pigment particles obtained from historic oil paintings with Ag colloids as the enhancing substrate. We demonstrate the first extractionless nonhydrolysis SERS study of oil paint as well as the potential of correlated SERS and fluorescence microscopy studies for the simultaneous identification of organic colorants and binding media in historic oil paintings.     

Integrate silver colloids with silicon nanowire arrays for surface-enhanced Raman scattering

A facile method to prepare uniform and reproducible surface-enhanced Raman scattering (SERS) substrates is presented. Quasi-spherical silver colloids prepared by microwave heating and wafer-scale uniform silicon nanowire (SiNW) arrays fabricated via wet chemical etching were united together as SERS substrates. The novel SERS substrates displayed stronger Raman enhancement than conventional silver colloids as well as outstanding uniformity and reproducibility in our experiments. In addition, it was found that the cross section of SiNW arrays possessed stronger enhancement activity than the front side. The enhancement effects of two adjacent SiNWs (as a simplification of SiNW arrays) were evaluated by the finite difference time domain (FDTD) method.     

Fluorescence and Raman study of pH effect on the adsorption orientations of methyl red on silver colloids

We report the fluorescence and surface-enhanced Raman scattering (SERS) analysis of methyl red (MR) isomers (o-MR, m-MR, p-MR) on silver (Ag) colloids at different pH conditions. The changes in simultaneous fluorescence quenching around 400 nm accompanied by enhancement around 540 nm with pH are closely related to energy transfer efficiency and the interaction between the carboxylic group and the Ag surface. The change of SERS signals with pH values can be ascribed to different adsorption orientations of MR on the Ag surface, from near flat (o-MR) to near perpendicular (p-MR).     

Hierarchical silver nanodendrites: One-step preparation and application for SERS

Without using any other reducing reagents or templates, a one-step approach for synthesizing dendritic Ag nanostructure by the treatment of sliver ions only in the presence of silk fibroin biomacromolecule is described. The morphology and structure of as-prepared silver nanodendrite are characterized, and its application for surface-enhanced Raman scattering (SERS) is also investigated. It has been found that the morphology of as-prepared Ag dendrite is dependent on the reaction duration, but not the concentration of sliver ions in the reaction process. SERS study shows that the silver nanodendrites give an intensive and enhanced Raman scattering when pyridine is used as a probing molecule. It is suggested that silk fibroin provides dual reductant and structure-directing roles to promote sliver ions forming shape-controlled nanostructures in high yield.     

Effect of oxidation on surface-enhanced Raman scattering activity of silver nanoparticles: a quantitative correlation

We quantitatively studied, using X-ray photoelectron spectroscopy (XPS), oxidation of substrate-immobilized silver nanoparticles (Ag NPs) in a wide range of conditions, including exposure to ambient air and controlled ozone environment under UV irradiation, and we correlated the degree of silver oxidation with surface-enhanced Raman scattering (SERS) enhancement factors (EFs). The SERS activity of pristine and oxidized Ag NPs was assessed by use of trans-1,2-bis(4-pyridyl)ethylene (BPE) and sodium thiocynate as model analytes at the excitation wavelength of 532 nm. Our study showed that the exposure of Ag NPs to parts per million (ppm) level concentrations of ozone led to the formation of Ag(2)O and orders of magnitude reduction in SERS EFs. Such an adverse effect was also notable upon exposure of Ag NPs under ambient conditions where ozone existed at parts per billion (ppb) level. The correlated XPS and SERS studies suggested that formation of just a submonolayer of Ag(2)O was sufficient to decrease markedly the SERS EF of Ag NPs. In addition, studies of changes in plasmon absorption bands pointed to the chemical enhancement as a major reason for deterioration of SERS signals when substrates were pre-exposed to ambient air, and to a combination of changes in chemical and electromagnetic enhancements in the case of substrate pre-exposure to elevated ozone concentrations. Finally, we also found UV irradiation and ozone had a synergistic effect on silver oxidation and thus a detrimental effect on SERS enhancement of Ag NPs and that such oxidation effects were analyte-dependent, as a result of inherent differences in chemical enhancements and molecular binding affinities for various analytes.     

溶胶-凝胶法载银SiO2杂化膜的制备及性能研究

采用溶胶-凝胶法,在甲基化改性的SiO2溶胶中掺杂硝酸银,制备Ag/M-SiO2杂化膜。通过XRD、XPS、紫外-可见吸收谱、N2吸附-脱附以及气体渗透性能测试等方法,考察了银掺杂对杂化膜结构和性能的影响。结果表明,Ag/M-SiO2膜中的银元素完全为纳米金属银,具有面心立方结构。金属银的掺杂对Ag/M-SiO2膜的化学结构基本没有影响,但使其孔径和总孔体积略微增大。与未载银的SiO2膜相比,Ag/M-SiO2膜具有更大的H2渗透速率和更好的H2/CO2选择性。金属银的引入增强了H2的表面扩散作用,促进了H2在膜中的传递,提高了SiO2膜的水汽稳定性。     

Fabrication of Ag–ZnO NRs SERS substrates for abamectin detection: the effect of Ag sputtering times and ZnO sol concentrations in seed layer preparation on SERS performance

Journal of Materials Science: Materials in Electronics - In this study, a surface-enhanced Raman scattering (SERS) substrate based on uniform silver nanoparticles/ZnO nanorods arrays (Ag–ZnO...     

Gold/palladium and silver/palladium colloids as novel metallic substrates for surface-enhanced Raman scattering

New surface-enhanced Raman scattering (SERS) substrates, composed of gold or silver colloidal nanoparticles doped with palladium, were prepared. These novel colloids are stable and maintain a satisfactory SERS efficiency, even after long aging. The interest in doping the coinage metal nanoparticles with palladium is due to the well-known catalytic activity of this metal. Transmission electron microscopy (TEM) and ultraviolet-visible absorption spectroscopy were used to characterize the shape and size of the metal particles. It was found that these bimetallic colloidal nanoparticles have a core-shell structure, with gold or silver coated with palladium clusters.     

Surface-enhanced Raman spectra of calf thymus DNA adsorbed on concentrated silver colloid

Raman and surface-enhanced Raman scattering (SERS) spectra of calf thymus DNA were investigated. We have carried out improvements to the silver colloid preparation method of Lee and Meisel in two respects. In one method, the silver sol was boiled with rapid stirring for over two hours. In the second method, the silver sol was concentrated by centrifugation before adding it to the DNA solution. The resulting hydrosol could be stored for 15 months because of its high stabilization. Structural information with respect to the phosphate backbone, deoxyribose, and four bases of DNA could be obtained before and after the DNA solutions were added to the concentrated Ag colloid substrate. The intensities of almost all characteristic bands assigned to various groups of the components of DNA were enhanced to a remarkable degree. The enhancement effect of the DNA solution at neutral pH 7.0 was obviously much better than that at acidic pH 3.4 or at alkaline pH 8.5. Intensity increases of the SERS bands of the DNA solution with time were observed. The SERS signals obtained 16 hours after the interaction of the Ag colloid with the DNA solution were much better than the SERS signals obtained just after the mixed liquid was prepared. This method can be widely used to store the Ag colloid for long times and to obtain the SERS spectra of DNA molecules, and it can further be used to study the adsorption behavior of solute biomacromolecules in different solvents.     

Silver clusters onto nanosized colloidal silica as novel surface-enhanced Raman scattering active substrates

A new method is proposed for obtaining surface-enhanced Raman scattering (SERS)-active substrates by photochemical reduction of silver nitrate onto colloidal silica. Transmission electron microscopy (TEM) and UV-visible absorption spectroscopy are employed to investigate the nanoscale structure of the materials. High quality SERS spectra are obtained from different organic ligands to check the efficiency of these substrates. A marked stability of the colloidal suspension is ensured by the scarce tendency of the Ag-doped silica particles to aggregate by either aging or adsorption of ligand.     

Fabricating Au–Ag core-shell composite films for surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) integrates high levels of sensitivity with spectroscopic precision, and thus, has tremendous potential for chemical and biomolecular sensing. The key to the wider application of Raman spectroscopy using roughened metallic surfaces is the development of highly enhancing substrates for analytical purposes, i.e., for better detection sensitivity of trace contaminants and pollutants. Here, we have prepared Au, Ag, AuAg multilayer, and Au@Ag films on glass substrates for SERS-active substrates. The Au@Ag film shows a much stronger SERS signal for trans-bis(4-pyridyl)ethylene (BPE) molecules than those from pure Au, Ag, and AuAg films, indicating the Au@Ag film is more powerful than pure Au, Ag, and AuAg film as SERS active substrates. The enhanced surface Raman scattering signals were attributed to the local field enhancement in the core-shell structure.