Improved performances on surface‐enhanced Raman scattering based on electrochemically roughened gold substrates modified with SiO2 nanoparticles

In this work, we use electrochemical oxidation–reduction cycles (ORC) methods to prepare surface‐enhanced Raman scattering (SERS)‐active gold substrates modified with SiO₂ nanoparticles to improve the corresponding SERS performances. Based on the modified substrates, the SERS of Rhodamine 6G (R6G) exhibits a higher intensity by 3‐fold of magnitude, as compared with that of R6G adsorbed on a SERS‐active Au substrate without the modification of SiO₂ nanoparticles. Moreover, the SERS enhancement capabilities of the modified and the unmodified Au substrates are seriously destroyed at temperatures higher than 250 and 200 °C, respectively. These results indicate that the modification of SiO₂ nanoparticles can improve the thermal stability of SERS‐active substrates. The aging in SERS intensity is also depressed on this modified Au substrate due to the contribution of SiO₂ nanoparticles to SERS effects. Copyright © 2009 John Wiley & Sons, Ltd.     

Enhancements in intensity and thermal stability of Raman spectra based on roughened gold substrates modified by underpotential deposition of silver

In this study, electrochemically roughened gold is modified with underpotential deposition (UPD) silver to investigate the effects on enhancements in the intensity and the thermal stability of surface‐enhanced Raman scattering (SERS). The SERS of Rhodamine 6G (R6G) adsorbed on the UPD Ag‐modified Au substrate exhibits a higher intensity by six‐fold of magnitude, as compared with that of R6G adsorbedon the unmodified Au substrate. Moreover, the SERS enhancement capabilities of UPD Ag‐modified Au and unmodified Au substrates are seriously depressed at temperatures higher than 200 and 150 °C, respectively. It indicates that the modification of UPD Ag can significantly depress the thermal destruction of SERS‐active substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering assessment of DNA from leaf tissues adsorbed on silver colloidal nanoparticles

In this work, the surface‐enhanced Raman scattering (SERS) spectra of seven genomic DNAs from leaves of chrysanthemum (Dendranthema grandiflora Ramat.), common sundew (Drosera rotundifolia L.), edelweiss (Leontopodium alpinum Cass), Epilobium hirsutum L., Hypericum richeri ssp. transsilvanicum (Čelak) Ciocârlan, rose (Rosa x hybrida L.) and redwood (Sequoia sempervirens D. Don. Endl.), respectively, have been analyzed in the wavenumber range 200–1800 cm⁻¹. The surface‐enhanced Raman vibrational modes for each of these cases, spectroscopic band assignments and structural interpretations of genomic DNAs are reported. A high molecular structural information content can be found in the SERS spectra of these DNAs from leaf tissues. Based on this work, specific plant DNA–ligand interactions or accurate local structure of DNA might be further investigated using surface‐enhanced Raman spectroscopy. Besides, this study will generate information which is valuable in the development of label‐free DNA detection for chemical probing in living cell. Copyright © 2013 John Wiley & Sons, Ltd.     

Ultrathin silver‐coated gold nanoparticles as suitable substrate for surface‐enhanced Raman scattering

Surface‐enhanced Raman scattering (SERS) is an extremely powerful tool for the analysis of the composition of bimetallic nanoparticle (BNP) surfaces because of the different adsorption schemes adopted by several molecules on different metals, such as Au and Ag. The preparation of BNPs normally implies a change in the plasmonic properties of the core metal. However, for technological applications it could be interesting to synthesize core–shell structures preserving these original plasmonic properties. In this work, we present a facile method for coating colloidal gold nanoparticles (NPs) in solution with a very thin shell of silver. The resulting bimetallic Au@Ag system maintains the optical properties of gold but shows the chemical surface affinity of silver. The effectiveness of the coating method, as well as the progressive silver enrichment of the outermost part of the Au NPs, has been monitored through the SERS spectra of several species (chloride, luteolin, thiophenol and lucigenin), which show different behaviors on gold and silver surfaces. A growth mechanism of the Ag shell is proposed on the basis of the spectroscopic and microscopic data consisting in the formation and deposit of Ag clusters on the Au NP surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Al2O3薄膜/纳米Ag颗粒复合结构的光吸收谱及增强Raman散射光谱研究

Al₂O₃介质薄膜与纳米Ag颗粒构成的复合结构,被应用于表面增强Raman散射探测实验中,其中Al₂O₃介质薄膜对纳米Ag颗粒的吸收谱及增强Raman散射光谱的影响被特别关注.该复合结构的光学特性表征出纳米Ag颗粒的偶极振荡特性.从光吸收谱中可以看到,其共振吸收谱随Al₂O₃介质薄膜厚度增加而在整个谱域上发生红移,表明纳米Ag颗粒的周围介电常数随Al₂O₃介质薄膜厚度的增加而增大.采用罗丹明6G作为探针原子,6个Raman特征峰的平均增益值作为表征表面增强Raman散射衬底增益程度的量度.实验结果表明,Al₂O₃介质薄膜层的引入提高了纳米Ag颗粒的衬底介电常数,并引起了散射共振的增强,从而使表面增强Raman散射强度提高. 关键词： 纳米Ag薄膜 共振吸收 表面增强Raman散射 介电常数     

Surface enhanced Raman scattering of 2-cyanopyridine adsorbed on silver colloidal particles

Surface-enhanced Raman scattering (SERS) spectra of 2-cyanopyridine (2 CP) adsorbed on silver colloidal particles have been investigated. The prominent SERS bands are observed at 556, 612, 778, 1002, 1060, 1072, 1150 and 1240 cm⁻¹. The absolute enhancement factor of the Raman signals in SERS studies has been estimated to be of the order of 10²–10⁵ for various bands. The 2CP molecules have been ascribed to adsorb on colloidal particles in standing up fashion.     

Raman scattering of L‐tryptophan enhanced by surface plasmon of silver nanoparticles: vibrational assignment and structural determination

Vibrational bands of L ‐tryptophan which was adsorbed on Ag nanoparticles (∼10 nm in diameter) have been investigated in the spectral range of 200–1700 cm⁻¹ using surface‐enhanced Raman scattering (SERS) spectroscopy. Compared with the normal Raman scattering (NRS) of L ‐tryptophan in either 0.5 M aqueous solution (NRS‐AS) or solid powder (NRS‐SP), the intensified signals by SERS have made the SERS investigation at a lower molecular concentration (5 × 10⁻⁴ M ) possible. Ab initio calculations at the B3LYP/6‐311G level have been carried out to predict the optimal structure and vibrational wavenumbers for the zwitterionic form of L ‐tryptophan. Facilitated with the theoretical prediction, the observed vibrational modes of L ‐tryptophan in the NRS‐AS, NRS‐SP, and SERS spectra have been analyzed. In the spectroscopic observations, there are no significant changes for the vibrational bands of the indole ring in either NRS‐AS, NRS‐SP, or SERS. In contrast, spectral intensities involving the vibrations of carboxylate and amino groups are weak in NRS‐AS and NRS‐SP, but strong in SERS. The intensity enhancement in the SERS spectrum can reach 10³–10⁴‐fold magnification. On the basis of spectroscopic analysis, the carboxylate and amino groups of L ‐tryptophan are determined to be the preferential terminal groups to attach onto the surfaces of Ag nanoparticles in the SERS measurement. Copyright © 2008 John Wiley & Sons, Ltd.     

Al2O3薄膜/纳米Ag颗粒复合结构的光吸收谱及增强Raman散射光谱研究

Al₂O₃介质薄膜与纳米Ag颗粒构成的复合结构,被应用于表面增强Raman散射探测实验中,其中Al₂O₃介质薄膜对纳米Ag颗粒的吸收谱及增强Raman散射光谱的影响被特别关注.该复合结构的光学特性表征出纳米Ag颗粒的偶极振荡特性.从光吸收谱中可以看到,其共振吸收谱随Al₂O₃介质薄膜厚度增加而在整个谱域上发生红移,表明纳米Ag颗粒的周围介电常数随Al₂O₃介质薄膜厚度的增加而增大.采用罗丹明6G作为探针原子,6个Raman特征峰的平均增益值作为表征表面增强Raman散射衬底增益程度的量度.实验结果表明,Al₂O₃介质薄膜层的引入提高了纳米Ag颗粒的衬底介电常数,并引起了散射共振的增强,从而使表面增强Raman散射强度提高.     

Surface‐enhanced Raman scattering on silver dendrite with different growth directions

A simple and cost‐effective strategy was developed to synthesize Ag dendrites via an aqueous chemical route based on spontaneous galvanic displacement between silver (I) ions and copper foil under hydrothermal condition. Ag dendrites with [100], [110], and [111] growth direction can be prepared by adjusting the content of polyvinyl pyrrolidone. The Ag dendrites exhibited fine and well reproducible surface‐enhanced Raman scattering effect using Rhodamine 6G as model molecule. There is a corresponding relation between the false color plot of Raman intensity and the dendrite morphology. Among the products, the Ag dendrites growing along [100] direction have the best surface enhancement ability, and a possible explanation was proposed. The results might open up new thinking on surface‐enhanced Raman scattering by proper crystal growth and design. Copyright © 2011 John Wiley & Sons, Ltd.     

非水体系中哌啶在银电极表面的表面增强喇曼散射

本文测定了哌啶在甲醇溶液中吸附在银电极表面的表面增强喇曼散射(SERS)光谱,及其随电位的变化,同时还测定了电极经不同氧化-还原循环(ORC)预处理时的SERS谱,对所得结果进行了分析比较,并进一步研究了非水体系和水体系SERS谱之间的关系.实验结果表明:哌啶在甲醇体系中比在水体系中SERS谱的增强因子要小,并且它们的SERS谱线随电位的变化也有一定的差别.     

Enhancement of Raman scattering of light by ultramarine microcrystals in presence of silver nanoparticles

Approximately 10²‐fold enhancement of Raman scattering by ultramarine microcrystals is reported by means of interaction with silver nanoparticles in films and powders. Theoretical modeling predicts the maximal 10¹⁰‐fold enhancement in close vicinity of a silver spherical nanoparticle (0.24 nm) with rapid decay of enhancement factor to 1 in the range of approximately 50 nm. Experimental enhancement factor is treated as overall effect within the small portion of every microcrystal in the close vicinity of silver nanoparticle(s). The results are considered as an important extension of traditional surface enhanced molecular Raman spectroscopy towards bigger inorganic probes. Copyright © 2012 John Wiley & Sons, Ltd.     

Microstructured polymer‐based substrates with broadband absorption for surface‐enhanced Raman scattering

Large area (3 × 3 cm²) substrates for surface‐enhanced Raman scattering were fabricated by combining femtosecond laser microstructuring and soft lithography techniques. The fabrication procedure is as follows: (i) femtosecond laser machining is used to create a silicon master copy, (ii) replicates from polydimethylsiloxane are made, and (iii) a 50‐nm‐thick gold film is deposited on the surface of the replicates. The resulting substrates exhibit strongly enhanced absorption in the spectral region of 350 ∼ 1000 nm and generate enhanced Raman signal with enhancement factor of the order of 10⁷ for 10^{‐ 6} M rhodamine 6G. The main advantages of our substrates are low cost, large active area, and possibility for mass replication. Copyright © 2013 John Wiley & Sons, Ltd.     

基于银胶纳米颗粒的痕量三硝基甲苯的表面增强拉曼光谱的实验研究

近年来对作为典型的硝基苯环类炸药的三硝基甲苯(TNT)的痕量检测受到越来越多的关注。将银胶纳米颗粒作为表面增强拉曼散射(SERS)基底,研究了10-6 mol.L-1的TNT的表面增强拉曼光谱的优化实验条件,重点研究了氯化钠溶液(NaCl)的含量以及碱性水解对TNT的表面增强拉曼光谱的影响。实验发现SERS样品中如果没有加入NaCl溶液,将观察不到TNT的SERS谱。加入的NaCl的含量必须在某一个范围之内才能观察到TNT的SERS谱,而且在这个范围之内,随着NaCl含量的增加,TNT的1 392cm-1处的拉曼峰出现先增大后减小的现象。对NaCl在TNT的SERS中的作用给予了理论解释。研究还发现TNT分子经过碱性水解后,与银纳米颗粒之间的吸附作用增强,其SERS谱的强度明显优于未经碱性水解的SERS结果。     

Surface‐enhanced Raman scattering of silylated graphite oxide sheets sandwiched between colloidal silver nanoparticles and silver piece

Graphite oxide (GO) was successfully silylated by 3‐mercaptopropyltrimethoxysilane. The surface‐enhanced Raman scattering spectrum of the silylated GO sheets sandwiched between colloidal silver nanoparticles and silver piece is presented. The Raman signal shows a 10⁴ enhancement compared to that of bulk GO. The large Raman enhancement is most likely a result of electromagnetic (EM) coupling between the colloidal silver nanoparticles (localized surface plasmon) and the silver piece (surface plasmon polariton), creating large localized EM fields at their interface, where the silylated GO sheets reside in this sandwich architecture. Copyright © 2009 John Wiley & Sons, Ltd.     

Improved surface-enhanced Raman scattering of patterned gold nanoparticles deposited on silicon nanoporous pillar arrays

Large-area silicon nanoporous pillar arrays (Si-NPA) uniformly coated with gold nanoparticles was synthesized, and surface-enhanced Raman scattering of rhodamine 6G adsorbed on these gold nanoparticles were studied and compared. It's found that Au/Si-NPA substrate has a significantly high Raman signal sensitivity and good homogeneity. These are attributed to gold nanoparticles with narrow particle-size distribution uniformly coated on the surface and to the enlarged specific surface area for adsorption of target molecules brought by the porous silicon pillars.     

Deposition of Ag nanoparticles on porous anodic alumina for surface enhanced Raman scattering substrate

Ag nanoparticles were exclusively deposited inside the pores of the porous anodic alumina (PAA) template through the deposition cycle including the incubation and the subsequent reduction of Ag(NH₃) . Both the density and size of the produced Ag nanoparticles increased as the deposition cycle number increased. A field‐emission scanning electron microscopeand an ultraviolet‐visible spectrometer were applied, respectively, to study the morphology and the extinction spectra of the Ag nanoparticles. The optimum deposition number was found from the scanning electron microscope (SEM) analysis. Surface enhanced Raman scattering (SERS) spectra of p‐aminothiophenol recorded on the Ag–PAA substrates prepared under increasing number of deposition cycles, manifested an enlarging trend of peak intensity. A point‐by‐point SERS mapping of p‐aminothiophenol on the Ag–PAA substrate was acquired to characterise the homogeneity of the substrate. Copyright © 2008 John Wiley & Sons, Ltd.     

A facile synthesis of branched silver nanowire structures and its applications in surface-enhanced Raman scattering

We report a facile method of preparing novel branched silvernanowire structures such as Y-shaped, K-shaped and other multi-branchednanowires. These branched nanostructures are synthesized by reducingsilver nitrate (AgNO₃) in polyethylene glycol(PEG) with polyvinglpyrrolidone (PVP) as capping agent. Statisticaldata indicate that for the “y” typed branched nanowire,the branches grow out from the side of the trunk nanowire in a preferentialorientation with an angle of 55? between the branch and the trunk.Transmission electron microscopy (TEM) studies indicate that the defectson silver nanowires could support the growth of branched nanowires.Conditions such as the molar ratio of PVP/AgNO₃, the reaction temperature, and the degree of polymerization of reducingagent and PVP play important roles in determining the yield of thesilver branches. Due to the rough surface, these branched nanostructurescan be used as efficient substrates for surface-enhanced Raman scatteringapplications.     

Surface‐enhanced Raman scattering of N‐acetylneuraminic acid on silver nanoparticle surface

N‐Acetylneuraminic acid (sialic acid, Neu5Ac) has recently gained interest as a potential marker for a variety of pathophysiological processes, although no Raman study has been reported for this important biomolecule. In this paper, the vibrational properties of Neu5Ac were studied by means of Raman, surface‐enhanced Raman scattering (SERS), and density functional theory calculations. By adsorption of Neu5Ac on silver nanoparticle surface, strongly enhanced Raman intensities are obtained, allowing easy measurement of small amounts of aqueous Neu5Ac (10 µl of a 10⁻⁷ m solution) utilizing low laser power and short exposure time. The mechanism of adsorption of Neu5Ac on the silver surface is discussed on the basis of the experimental and theoretical results. This study demonstrates that SERS can provide an effective tool for development of a label‐free, rapid, and sensitive optical platform for identification of Neu5Ac. Copyright © 2014 John Wiley & Sons, Ltd.     

Simple method to prepare size‐controllable gold nanoparticles in solutions and their applications on surface‐enhanced Raman scattering

We report here, for the first time, a simple method to prepare size‐controllable Au nanoparticles (NPs) in aqueous solutions from bulk Au substrates. First, chitosan (Ch)‐capped Au‐containing complexes were prepared by electrochemical oxidation–reduction cycles in 0.1 N NaCl and 1 g/l Ch solutions. Then the solutions were heated from room temperature to boiling at different heating rates to synthesize size‐controllable Au NPs. The particle sizes of the prepared Au(111) NPs could be controlled from 5 to 30 nm with an increase of the heating rate during preparation. Experimental results indicate that the prepared Au(111) NPs with diameters ranging from 10 to 30 nm can serve as surface‐enhanced Raman scattering active probes for molecules of rhodamine 6G. Copyright © 2010 John Wiley & Sons, Ltd.     

An effective surface-enhanced Raman scattering template based on gold nanoparticle/silicon nanowire arrays

A large-scale Si nanowire array （SiNWA） is fabricated with gold （Au） nanoparticles by simple metal-assisted chemical etching and metal reduction processes. The three-dimensional nanostructured Au/SiNWA is evaluated as an active substrate for surface-enhanced Raman scattering （SERS）. The results show that the detection limit for rhodamine 6G is as low as 10-7 M, and the Raman enhancement factor is as large as 105 with a relative standard deviation of less than 25%. After the calibration of the Raman peak intensifies of rhodamine 6G and thiram, organic molecules could be quantitatively detected. These results indicate that Au/SiNWA is a promising SERS-active substrate for the detection of biomolecules present in low concentrations. Our findings are an important advance in SERS substrates to allow fast and quantitative detection of trace organic contaminants.