Gold particle interaction in regular arrays probed by surface enhanced Raman scattering

Lithographically designed two-dimensional arrays consisting of gold nanoparticles deposited on a smooth gold film are used as substrate to examine the SERS effect of the trans-1,2-bis (4-pyridyl) ethylene molecule. These arrays display two plasmon bands instead of the single one observed for the same arrays of particles but deposited on indium tin oxide coated glass. Laser excitation within the short wavelength band does not bring about any SERS spectrum, while excitation within the long wavelength band yields SERS spectra with a gain per molecule rising up to 10(8). The simultaneous investigation of extinction and Raman spectra of arrays exhibiting various topography parameters enables us to suggest an interpretation for both the occurrence of the two plasmon resonances and for the high Raman enhancement. We suggest to assign the short wavelength band to a plasmon wave propagating at the gold glass interface and the long wavelength one to an air/gold surface plasmon mode modified by particle-particle interaction.     

A new substrate for surface enhanced Raman scattering of dye Sudan molecules

A new SERS substrate was prepared using electro-polishing aluminum foils. Based on these high active SERS systems, surface enhanced Raman scattering (SERS) of Azo Dye Sudan were performed and carefully studied based on this highly active SERS substrate. High quality SERS spectra were obtained, which indicates that this kind of coarse aluminum foils is an active SERS substrate. Numbers of additional modes were presented, as well as some split peaks, which may be a consequence of symmetry lowering.     

Insulin amyloid superstructures as templates for surface enhanced Raman scattering

Nanostructuring of noble metal surfaces with biomorphic and biological templates facilitates a variety of applications of surface enhanced Raman scattering (SERS). Here we show that the newly reported insulin amyloid superstructures may be employed as stable nanoscaffolds for metallic Au films providing an effective substrate for SERS on covalently bound molecules of 4-mercaptobenzoic acid (4-MBA). The vortex-aligned insulin fibrils are capable of templating nanopatterns in sputtered Au layers without overlapping the SERS spectra of 4-MBA with vibrational bands stemming from the protein. This holds true regardless of whether the incident laser beam is directly backscattered from the 4-MBA layer, or after passage through the insulin amyloid layer.     

Gold nanoparticle-based surface enhanced Raman scattering spectroscopic assay for the detection of protein-protein interactions

In the present work, a sensitive spectroscopic assay based on surface-enhanced Raman spectroscopy (SERS) using gold nanoparticles as substrates was developed for the rapid detection protein-protein interactions. Detection is achieved by specific binding biotin-modification antibodies with protein-stabilized 30 nm gold nanoparticles, followed by the attachment of avidin-modification Raman-active dyes. As a proof-of-principle experiment, a well-known biomolecular recognition system, IgG with protein A, was chosen to establish this new spectroscopic assay. Highly selective recognition of IgG down to 1 ng/ml in solution has been demonstrated.     

Quantitative surface enhanced Raman scattering detection based on the "sandwich" structure substrate

A sandwich structured substrate was designed for quantitative molecular detection using surface enhanced Raman scattering (SERS), in which the probe molecule was sandwiched between silver nanoparticles (SNPs) and silver nanoarrays. The SNPs was prepared using Lee-Meisel method, and the silver nanoarrays was fabricated on porous anodic aluminum oxide (AAO) using electrodepositing method. The SERS studies show that the sandwich structured substrate exhibits good stability and reproducibility, and the detection sensitivity of Rhodamine 6G (R6G) and Melamine can respectively reach up to 10(-19) M and 10(-9) M, which is improved greatly as compared to other SERS substrates. The improved SERS sensitivity is closely associated with the stronger electromagnetic field enhancement, which stems from localized surface plasmon (LSP) coupling between the two silver nanostructures. Furthermore, the SERS intensity increased almost linearly as the mother concentration increased, which indicates that such a sandwich structure may be used as a good SERS substrate for quantitative analysis.     

Surface enhanced Raman scattering based on silver dendrites substrate

A simple method of the reduction of AgNO3 by copper foil in aqueous medium was used to prepare silver dendrites, which can be used as a novel good reproducible surface enhanced Raman scattering (SERS) active substrate. The SERS spectra of 4-pyridinethiol on this novel substrate reflected the different SERS activities on the minuteness and strong Ag dendrites. The electromagnetic coupling enhancement and chemical enhancement mechanisms are used to explain the SERS effect.     

Laser-MBE of nickel nanowires using AAO template: a new active substrate of surface enhanced Raman scattering

The highly ordered anodic aluminum oxide (AAO) template was fabricated using aluminum anodizing in electrolytes with two-step method, which apertures were about 50-80nm. The nickel nanowires with about 40-70nm in diameter was prepared on the AAO template by laser-MBE (molecular beam epitaxy). And high quality Raman spectra of SudanII were obtained on the glass covered with the nickel nanowires. On the nickel nanowires there are both surface enhanced Raman scattering (SERS) and tip enhanced Raman scattering (TERS). The new observations not only enlarge the range of SERS applications, but also imply a possible new enhancement mechanism. Otherwise the Raman and SERS frequencies of SudanII molecule were calculated using, respectively, DFT and B3PW91.     

Nanoparticle-containing structures as a substrate for surface-enhanced Raman scattering

Metallic nanostructures were prepared through the alternate immersion of derivatized glass slides in solutions of gold nanoparticles (NPs) and a propanedithiol linker molecule. Nanostructures consisting of 1-17 depositions of gold NPs were synthesized, and these substrates were characterized using UV-vis spectroscopy and atomic force microscopy. Subsequently, the surface-enhanced Raman scattering (SERS) of oxazine 720 was obtained at two excitation wavelengths (632 and 785 nm) from all substrates. Maximum SERS enhancement was observed for 9 and 13 NP depositions for 632 and 785 nm excitations, respectively. The difference in the number of NP depositions required for maximum enhancement is attributed to different wavelengths which can excite distinct aggregate structures within the metallic substrate. Therefore, these NP-containing structures can be "tuned" to yield maximum SERS enhancement for the excitation source being used by varying the number of NP depositions.     

基于聚合物／金属纳米结构镶嵌型柔性基底的表面增强拉曼光谱技术

表面增强拉曼光谱（SERS）技术可极大增强传统拉曼光谱的信号强度,从而拓展拉曼光谱的应用范围．针对SERS技术在分析对象、分析环境的普适性和分析效率方面的限制,本文设计并发展了一种透明、柔性、自支撑SERS基底的制备、保存和使用方法．该基底由聚合物聚甲基丙烯酸甲酯（PMMA）和在其表面镶嵌的金属纳米结构组成,可以通过背入射法用于任意形貌样品表面的直接和在线检测．柔性SERS（Ag）基底在R6G水溶液表面的检测限小于1pmol／L．     

Practical understanding and use of surface enhanced Raman scattering/surface enhanced resonance Raman scattering in chemical and biological analysis

The unique ability to obtain molecular recognition of an analyte at very low concentrations in situ in aqueous environments using surface enhanced Raman scattering (SERS) and surface enhanced resonance Raman scattering (SERRS) detection makes these spectroscopies of considerable interest. Improved understanding of the effect coupled to improvements in practical techniques make the use of SERS/SERRS much simpler than has been the case in the past. This article is designed as a tutorial review targeted at aiding in the development of practical applications.     

Preparative isotachophoresis with surface enhanced Raman scattering as a promising tool for clinical samples analysis

A surface enhanced Raman scattering (SERS) spectrometry is an interesting alternative for a rapid molecular recognition of analytes at very low concentration levels. The hyphenation of this technique with advanced separation methods enhances its potential as a detection technique. Until now, it has been hyphenated mainly with common chromatographic and electrophoretic techniques. This work demonstrates for a first time a power of preparative isotachophoresis-surface enhanced Raman scattering spectrometry (pITP-SERS) combination on the analysis of model analyte (buserelin) in a complex biological sample (urine). An off-line identification of target analyte was performed using a comparison of Raman spectra of buserelin standard with spectra obtained by the analyses of the fractions from preparative isotachophoretic runs. SERS determination of buserelin was based on the method of standard addition to minimize the matrix effects. The linearity of developed method was obtained in the concentration range from 0.2 to 1.5 nmol L(-1) with coefficient of determination 0.991. The calculated limit of detection is in tens of pico mols per liter.     

Lithographically-defined 3D porous networks as active substrates for surface enhanced Raman scattering

Interferometric lithographically fabricated porous carbon acts as active substrates for Surface Enhanced Raman Scattering (SERS) applications with enhancement factors ranging from 7 to 9 orders of magnitude.     

Electrochemical fabrication of two-dimensional palladium nanostructures as substrates for surface enhanced Raman scattering

Two-dimensional palladium (Pd) nanostructures have been fabricated by electrochemical deposition of Pd onto an indium tin oxide glass substrate modified with a thin flat film of polypyrrole or a nanofibril film of polyaniline. The experimental results demonstrated that the morphology of Pd nanoparticles strongly depended on the properties of conducting polymers and the conditions of electrochemical deposition. Two-dimensional nanostructures composed of flower-like (consisting of staggered nanosheets) or pinecone-like Pd nanoparticles were successfully synthesized. They can be used as substrates for surface-enhanced Raman scattering after partly decomposing the polymer components by heating in air, and the enhancement factor of the substrate composed of flower-like Pd nanoparticles was measured to be as high as 105 for 4-mercaptopyridine.     

Metal-molecule Schottky junction effects in surface enhanced Raman scattering

We propose a complementary interpretation of the mechanism responsible for the strong enhancement observed in surface enhanced raman scattering (SERS). The effect of a strong static local electric field due to the Schottky barrier at the metal-molecule junction on SERS is systematically investigated. The study provides a viable explanation to the low repeatability of SERS experiments as well as the Raman peak shifts as observed in SERS and raw Raman spectra. It was found that a strong electrostatic built-in field at the metal-molecule junction along specific orientations can result in 2-4 more orders of enhancement in SERS.     

Water soluble gold-polyaniline nanocomposite: A substrate for surface enhanced Raman scattering and catalyst for dye degradation

In this work, a water-soluble gold nanoparticle-encapsulated polyaniline nanocomposite (AuNP-PANI) was prepared in the presence of an ionic surfactant such as cetyltrimethylammonium bromide (CTAB) using versatile two steps method. The prepared nanoparticles (AuNPs) were characterized by UV–Visible spectroscopy, Transmission Electron Microscope (TEM) and Dynamic Light Scattering (DLS). The nanocomposite (AuNP-PANI) were initially characterized using UV–Visible spectroscopy, Transmission Electron Microscope (TEM), Scanning Transmission Electron Microscope (STEM) and DLS. The structure and composition of AuNP-PANI further characterized using Fourier Transmission Infrared Spectroscopy (FTIR), X-ray diffraction study (XRD), Energy Dispersive X-ray Spectroscopy (EDS) and Thermogravimetric analysis (TGA). Electrochemical properties of AuNP-PANI were studied using Cyclic Voltammetry (CV). The prepared nanocomposite exhibited good surface enhanced Raman scattering (SERS) of 4-amino thiophenol (4-ATP) and 4- (dimethyl amino) pyridine (4-DMAP) for which the enhancement factor (EF) were found to be1.95 × 10⁵ and 2.016 × 10⁵, respectively. The nanocomposite also showed excellent catalytic activity for the chemical degradation of Congo red (CR) and methylene blue (MB) as evidenced from the calculated rate constants which were determined to be 0.30 s⁻¹ and 0.33 s⁻¹, respectively.     

Vibrational pumping in surface enhanced Raman scattering (SERS)

In this tutorial review, the underlying principles of vibrational pumping in surface enhanced Raman scattering (SERS) are summarized and explained within the framework of their historical development. Some state-of-the-art results in the field are also presented, with the aim of giving an overview on what has been established at this stage, as well as hinting at areas where future developments might take place.     

Microspectrometric investigation of active substrates for surface enhanced Raman scattering

The results of investigations of several new active silver substrates and some previously reported active silver substrates for surface enhanced Raman spectrometry (SERS) using a Raman microprobe are given. Filter-papers of different composition and porosity, silver membranes and glass slides are evaluated as supports for SERS active substrates. Methods of silver preparation include evaporation and chemical reduction. The Raman microprobe facilitates the acquisition of SER spectra of the adsorbate over the metal microstructure being observed on a TV monitor. This capability allows the establishment of practical relationships between the surface morphology and SERS activity which can be used as guidelines for SERS experiments with the microprobe. For the most monodisperse substrates, it is possible to establish a linear relationship between SERS intensity and adsorbate concentration. In the lower extreme of the calibration graph, the amount of adsorbate being observed under the microscope objective is only 0.3 amol or 1.9 × 10⁵ molecules.     

Biosensing using silver nanoparticles and surface enhanced resonance Raman scattering

Silver nanoparticles can be used to provide excellent surface enhanced resonance Raman scattering. Control of the surface chemistry and the use of appropriate protocols enables effective sensing of biomolecules.     

Stokes/anti-Stokes anomalies under surface enhanced Raman scattering conditions

The possibility of achieving anti-Stokes stimulation and/or pumping under surface enhanced Raman scattering conditions has been the source of intense controversies in the literature. With the aim of clarifying some of the aspects of this problem, we study theoretically and experimentally the situation in a model system which highlights some of the difficulties in the interpretation of the data. We show that many of the assumptions often presumed in the literature need to be assessed with care in each case. Through careful experiments we show, in particular, that the anti-Stokes/Stokes ratio for a specific mode in the same sample can depend on the chosen laser wavelength. This latter effect is a manifestation of the influence of the internal plasmon resonances (hot spots) in the result. Different possibilities and further research directions are highlighted and discussed.     

Excitation spectra of surface enhanced Raman scattering on sols.

A phenomenological approach is described for practical computations of the excitation spectra in surface enhanced Raman scattering (SERS) obtained with aggregated metal colloids.