The formation of nanometer‐sized gaps between silver nanoparticles is critically important for optimal enhancement in surface‐enhanced Raman scattering (SERS). A simple approach is developed to generate nanometer‐sized cavities in a silver nanoparticle thin film for use as a SERS substrate with extremely high enhancement. In this method, a submicroliter volume of concentrated silver colloidal suspension stabilized with cetyltrimethylammonium bromide (CTAB) is spotted on hydrophobic glass surfaces prepared by the exposure of the glass to dichloromethysilane vapors. The use of a hydrophobic surface helps the formation of a more uniform silver nanoparticle thin film, and CTAB acts as a molecular spacer to keep the silver nanoparticles at a distance. A series of CTAB concentrations is investigated to optimize the interparticle distance and aggregation status. The silver nanoparticle thin films prepared on regular and hydrophobic surfaces are compared. Rhodamine 6G is used as a probe to characterize the thin films as SERS substrates. SERS enhancement without the contribution of the resonance of the thin film prepared on the hydrophobic surface is calculated as 2×107 for rhodamine 6G, which is about one order of magnitude greater than that of the silver nanoparticle aggregates prepared with CTAB on regular glass surfaces and two orders of magnitude greater than that of the silver nanoparticle aggregates prepared without CTAB on regular glass surfaces. A hydrophobic surface and the presence of CTAB have an increased effect on the charge‐transfer component of the SERS enhancement mechanism. The limit of detection for rhodamine 6G is estimated as 1.0×10?8M . Scanning electron microscopy and atomic force microscopy are used for the characterization of the prepared substrate. 相似文献
Summary: Surface‐enhanced Raman scattering (SERS)‐active substrates with high enhancement were prepared by an in situ reduction method. Novel silver/poly(vinyl alcohol) (PVA) nanocomposite films were obtained, in which the silver nitrate, poly(γ‐glutamic acid) (PGA), and PVA acted as precursor, stabilizer, and polyol reducant, respectively. The UV‐visible spectra of the as‐fabricated films showed that the surface plasmon resonance (SPR) absorption band was narrow and of a stronger intensity, which indicates that the Ag nanoparticle size distribution on the substrate was highly uniform. This finding was further confirmed by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and field‐emission scanning electron microscope (FE‐SEM) measurements. It was found that a PGA‐stabilized PVA nanocomposite film revealed the presence of well‐dispersed spherical silver nanoparticles with an average diameter of 90 nm. The new substrate presents high SERS enhancement and the enhanced factor is estimated to be 106 for the detection of benzoic acid.
The Raman scattering enhancement factor for the Raman spectra of benzoic acid on the various nanocomposite films. 相似文献
Plasmonic nanomaterials possessing large‐volume, high‐density hot spots with high field enhancement are highly desirable for ultrasensitive surface‐enhanced Raman scattering (SERS) sensing. However, many as‐prepared plasmonic nanomaterials are limited in available dense hot spots and in sample size, which greatly hinder their wide applications in SERS devices. Here, we develop a two‐step physical deposition protocol and successfully fabricate 3D hierarchical nanostructures with highly dense hot spots across a large scale (6 × 6 cm2). The nanopatterned aluminum film was first prepared by thermal evaporation process, which can provide 3D quasi‐periodic cloud‐like nanostructure arrays suitable for noble metal deposition; then a large number of silver nanoparticles with controllable shape and size were decorated onto the alumina layer surfaces by laser molecular beam epitaxy, which can realize large‐area accessible dense hot spots. The optimized 3D‐structured SERS substrate exhibits high‐quality detection performance with excellent reproducibility (13.1 and 17.1%), whose LOD of rhodamine 6G molecules was 10?9 M. Furthermore, the as‐prepared 3D aluminum/silver SERS substrate was applied in detection of melamine with the concentration down to 10?7 M and direct detection of melamine in infant formula solution with the concentration as low 10 mg/L. Such method to realize large‐area hierarchical nanostructures can greatly simplify the fabrication procedure for 3D SERS platforms, and should be of technological significance in mass production of SERS‐based sensors. 相似文献
We report herein a method for the ultra‐trace detection of TNT on p‐aminothiophenol‐functionalized silver nanoparticles coated on silver molybdate nanowires based on surface‐enhanced Raman scattering (SERS). The method relies on π‐donor–acceptor interactions between the π‐acceptor TNT and the π‐donor p,p′‐dimercaptoazobenzene (DMAB), with the latter serving to cross‐link the silver nanoparticles deposited on the silver molybdate nanowires. This system presents optimal imprint molecule contours, with the DMAB forming imprint molecule sites that constitute SERS “hot spots”. Anchoring of the TNT analyte at these sites leads to a pronounced intensification of its Raman emission. We demonstrate that TNT concentrations as low as 10?12 M can be accurately detected using the described SERS assay. Most impressively, acting as a new type of SERS substrate, the silver/silver molybdate nanowires complex can yield new silver nanoparticles during the detection process, which makes the Raman signals very stable. A detailed mechanism for the observed SERS intensity change is discussed. Our experiments show that TNT can be detected quickly and accurately with ultra‐high sensitivity, selectivity, reusability, and stability. The results reported herein may not only lead to many applications in SERS techniques, but might also form the basis of a new concept for a molecular imprinting strategy. 相似文献
Surface enhancement mechanism of Raman scattering from molecules adsorbed on silver oxide colloids is reported. Absorption spectra and Raman spectra of the cyanine dye D266 and pyridine molecules adsorbed on Ag2O colloids, and the influences of S2O32− and OH− on the SERS are studied respectively. The results indicate that ‘chemical' enhancement is dominant in Ag2O colloidal solution. Surface complexes of adsorbed molecules and small silver ion clusters Agn+ as the SERS active sites make an important contribution to surface enhanced Raman scattering (SERS). At these active sites, charge transfer between the adsorbed molecules and the small silver ion clusters is the main enhancement origin. The enhancement factor of D266 adsorbed on Ag2O colloids is theoretically estimated with the excited-state charge transfer model, which is roughly in accordance with the experiments. 相似文献
Surface-enhanced Raman scattering (SERS) of graphene on a SiO(2)(300 nm)/Si substrate was investigated by depositing Au nanoparticles using thermal evaporation. This provided a maximum enhancement of 120 times for single-layer graphene at 633 nm excitation. SERS spectra and scan images of single-layer and few-layer graphene were acquired. Single-layer graphene provides much larger SERS enhancement compared to few-layer graphene, while in single-layer graphene the enhancement of the G band was larger than that of the 2D band. Furthermore, the D bands were identified in the SERS spectra; these bands were not observed in a normal Raman spectrum without Au deposition. Appearance of the D band is ascribed to the considerable SERS enhancement and not to an Au deposition-induced defect. Lastly, SERS enhancement of graphene on a transparent glass substrate was compared with that on the SiO(2)(300 nm)/Si substrate to exclude enhancement by multiple reflections between the Si substrate and deposited Au nanoparticles. The contribution of multiple reflections to total enhancement on the SiO(2)(300 nm)/Si substrate was 1.6 times out of average SERS enhancement factor, 71 times. 相似文献
Uniform phenolic resin microspheres were prepared by the polycondensation of 3-aminophenol and formaldehyde. On the surface of the 3-aminophenol resin microspheres, silver nanoparticles were synthesized in situ and immobilized by simple heating. The composite was employed as a substrate for surface-enhanced Raman scattering (SERS). The SERS enhancement factor was evaluated using 4-mercaptobenzoic acid and Nile blue A as signal molecules. A highly sensitive SERS immunoassay that combined labeled antibody conjugated silver nanoparticle modified 3-aminophenol resin microspheres and coating antibody conjugated magnetic nanoparticles was fabricated to determine carcinoembryonic antigen. A linear relationship was obtained between the Raman intensity and the concentration of carcinoembryonic antigen. The limit of detection was 1.2 picograms per milliliter at a signal-to-noise ratio of three. This is believed to be the first report of a SERS immunoassay using silver nanoparticle modified 3-aminophenol resin microspheres as substrates. 相似文献
Active surface-enhanced Raman scattering (SERS) silver nanoparticles substrate was prepared by multiple depositions of Ag nanoparticles on glass slides. The substrate is based on five depositions of Ag nanoparticles on 3-aminopropyl-trimetoxisilane (APTMS) modified glass slides, using APTMS sol–gel as linker molecules between silver layers. The SERS performance of the substrate was investigated using 4-aminobenzenethiol (4-ABT) as Raman probe molecule. The spectral analyses reveal a 4-ABT Raman signal enhancement of band intensities, which allow the detection of this compound in different solutions. The average SERS intensity decreases significantly in 4-ABT diluted solutions (from 10−4 to 10−6 mol L−1), but the compound may still be detected with high signal/noise ratio. The obtained results demonstrate that the Ag nanoparticles sensor has a great potential as SERS substrate. 相似文献
A thin‐film of dielectric on a reflecting surface constituting a multilayer substrate modulates light intensity due to the interference effect. A nanostructure consisting of randomly oriented silver particles of different shapes, sizes, and interparticle spacings supports multiple plasmon resonances and is observed to have a broad extinction spectrum that spans the entire visible region. Combining the two systems by fabricating the nanostructure on the thin‐dielectric film of the multilayer substrate yields a new composite structure which is observed to modulate both the extinction spectrum and the SERS EF (surface enhanced Raman scattering enhancement factor) of the nanostructure as the thickness of the thin‐film dielectric is varied. The frequency and intensity of the visible extinction spectrum vary dramatically with the dielectric thickness and in the intermediate thickness range the spectrum has no visible band. The SERS EF determined for the composite structure as a function of the thin‐film dielectric thickness varies by several orders of magnitude. Strong correlation between the magnitude of the SERS EF and the extinction intensity is observed over the entire dielectric thickness range indicating that the extinction spectrum corresponds to the excitation of the plasmon resonances of the nanostructure. A significant finding which has potential applications is that the composite structure has synergic effect to boost SERS EF of the nanostructure by an order of magnitude or more compared to the same nanostructure on an unlayered substrate.相似文献
We report on the fabrication of a surface‐enhanced Raman scattering (SERS) platform, comprised of a three‐dimensional (3D) porous eggshell membrane (ESM) scaffold decorated with Ag nanoparticles (NPs). Both native and treated ESM were used, where the treated ESM pore size and fiber crossing density was controlled by timed exposure to hydrogen peroxide (H2O2). Ag NPs were synthesized in situ by reduction of silver nitrate with ascorbic acid. Our results demonstrate that H2O2‐treated Ag‐ESM provides a more densely packed 3D network of active material, which leads to consistently higher SERS enhancement than untreated Ag‐ESM substrates. 相似文献
We report on the formation of silver subsurface ion‐exchanged metal oxide (silver SIMO) glasses and their surface‐enhanced Raman scattering (SERS) activity. The samples were prepared by a combined thermal and chemical three‐step methodology and characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), environmental electron scanning microscopy (ESEM), and UV/Vis spectroscopy. This unique method provides SERS substrates with protection against contamination and strong, reliable and reproducible SERS enhancement. The Raman enhancement factors of the long‐term stable SIMO glasses were estimated to approximately 107. 相似文献
Surface‐enhanced Raman spectroscopy (SERS) is an emerging technology in the field of analytics. Due to the high sensitivity in connection with specific Raman molecular fingerprint information SERS can be used in a variety of analytical, bioanalytical, and biosensing applications. However, for the SERS effect substrates with metal nanostructures are needed. The broad application of this technology is greatly hampered by the lack of reliable and reproducible substrates. Usually the activity of a given substrate has to be determined by time‐consuming experiments such as calibration or ultramicroscopic studies. To use SERS as a standard analytical tool, cheap and reproducible substrates are required, preferably with a characterization technique that does not interfere with the subsequent measurements. Herein we introduce an innovative approach to produce low‐cost and large‐scale reproducible substrates for SERS applications, which allows easy and economical production of micropatterned SERS active surfaces on a large scale. This approach is based on an enzyme‐induced growth of silver nanostructures. The special structural feature of the enzymatically deposited silver nanoparticles prevents the breakdown of SERS activity even at high particle densities (particle density >60 %) that lead to a conductive layer. In contrast to other approaches, this substrate exhibits a relationship between electrical conductivity and the resulting SERS activity of a given spot. This enables the prediction of the SERS activity of the nanostructure ensemble and therewith the controllable and reproducible production of SERS substrates of enzymatic silver nanoparticles on a large scale, utilizing a simple measurement of the electrical conductivity. Furthermore, through a correlation between the conductivity and the SERS activity of the substrates it is possible to quantify SERS measurements with these substrates.相似文献
In this work, we proposed a novel three-dimensional (3D) plasmonic nanostructure based on porous graphene/nickel foam (GNF) and gas-phase deposited Ag nanoparticles (NPs).Ag NPs with high density were directly deposited on the surface of 3D GNF by performing a novel cluster beam deposition approach. In comparison with traditional Ag substrate(SiO2/Ag), such hot-spots enriched 3D nanostructure showed extremely high electromag-netic field enhancement under incident light irradiation which could be used as a sensitive chemical sensor based on surface enhanced Raman scattering (SERS). The experimental results demonstrated that the proposed nanostructure showed superior SERS performance in terms of Raman signal reproducibility and sensitivity for the probe molecules. 3D full-wave simulation showed that the enhanced SERS performance in this 3D hierarchical plasmonic nanostructure was mainly obtained from the hot-spots between Ag NPs and the near-field coupling between Ag NPs and GNF sca olds. This work can provide a novel assembled SERS substrate as a SERS-based chemical sensor in practical applications. 相似文献
Surface Enhanced Raman Spectroscopy (SERS) is a valuable analytical tool for the investigation of molecules adsorbed on roughened noble metal surfaces. The shape, size, and surrounding of the metal protrusions play an important role in the Raman scattering enhancement. By combining scanning near-field optical microscopy (SNOM) with Raman spectroscopy the spatial resolution suffices for investigating isolated silver islands on SERS active substrates. We demonstrate an optical resolution below 70 nm for recording spectra on specifically prepared and fully characterized SERS substrates. For a quantitative evaluation of the SERS signal the spatial distribution of Rhodamine 6G (R6G) deposited on the SERS substrate was determined by friction force measurements. By comparing the Raman intensities of the SERS substrates with those of unmetallized support plates absolute SERS enhancement factors at specific locations on top and in the vicinity of the silver islands were determined directly. 相似文献