Surface-enhanced Raman Scattering from Molecules Adsorbed on Mixed Silver/Gold Nanoparticle Surfaces

Introduction Since the first discovery of Surface-Enhanced Raman Scattering(SERS) from pyridine molecules adsorbed at roughened silver electrodes in 1974 by Fleischmann et al.[1],the research of SERS has made tremendous progress in applications of it to various fields of science and technology[2-8].     

Au/Ag核-壳结构纳米粒子的制备及其SERS效应

随着大量有关表面增强拉曼散射 (SERS)的实验和理论研究的开展 ,金属纳米粒子作为一类重要的 SERS增强介质 ,已引起了人们浓厚的研究兴趣 [1] .而 Au和 Ag作为最常用的活性基底物质 ,更是研究的热点 [2 ,3 ] .最近 ,美国印第安那大学的 Nie等 [4 ] 在单个银纳米粒子上 ,观察到高达 1 0 14 ～ 1 0 15的SERS因子 .同时 ,他们的另外一项工作表明银纳米粒子的形状和大小对 SERS活性有很大影响 [5] .但是 ,由于 Ag溶胶制备的重复性较差 ,且粒度分布不均匀 ,通过控制银颗粒大小而调控 SERS活性是相当困难的[6] .与 Ag相比 ,Au在可见光…     

金纳米粒子修饰的氨基硅胶整体柱的制备及超灵敏表面增强拉曼散射检测

采用溶胶-凝胶法结合超分子模板技术, 以四乙氧基硅烷(TEOS)和3-氨丙基三乙氧基硅烷(APTES)作为反应前体, 以十六烷基三甲基溴化铵(CTMAB)为超分子模板, 简单快速地制备了一种新型氨基硅胶整体柱, 通过氨基将金纳米粒子组装在整体柱材料孔表面并用于表面增强拉曼散射(SERS)光谱分析. 以对巯基苯胺(PATP)和结晶紫(CV)为拉曼探针, 考察了金纳米粒子修饰的氨基硅胶整体柱用作SERS活性基底的性能. 结果表明, 该整体柱基底具有良好的SERS增强效应, 可检测到的PATP和CV的最低浓度分别为10^-9和10^-11 mol/L. 与金溶胶SERS基底相比, 本文制备的整体柱基底的检测灵敏度显著提高, 并具有良好的信号均一性, 是一种具有现场痕量检测应用潜力的SERS活性基底.     

Comparison of Surface-enhanced Raman Scattering Spectra of Two Kinds of Silver Nanoplate Films

Surface-enhanced Raman scattering(SERS) spectra of different silver nanoplate self-assembled films at different excitation wavelengths were fairly compared. Shape conversion from silver nanoprisms to nanodisks on slides was in situ carried out. The SERS spectra of 4-mercaptopyridine(4-MPY) on these anisotropic silver nanoparticle self-assembled films present that strong enhancement appeared when the excitation line and the surface plasmon resonance(SPR) band of silver substrate overlapped. In this model, the influence of the crystal planes of silver nanoplates on SERS enhancement could be ignored because the basal planes were nearly unchanged in two kinds of silver nanoplate self-assembled films.     

复合SERS基底的构建及性质

通过自组装方法以对巯基苯胺(PATP)为偶联分子, 在石英基片上构筑了多种形貌的银钠米粒子单层结构和三明治结构. 研究了组装膜在不同激发线下表面增强拉曼散射(SERS)的增强差异. 研究结果表明, 单层基底和三明治基底中偶联分子的SERS信号因银纳米粒子间的电磁场耦合而显著增强, 且在三明治结构中增强更加明显. 对复合SERS基底增强因子进行计算可知, 复合SERS基底的表面等离子体共振(SPR)峰与激发线的匹配程度越好, 其增强因子越大. 在三明治结构中更易发生PATP分子转变为对巯基偶氮苯(DMAB)分子的激光诱导催化偶联反应. 另外, 该激光诱导催化偶联反应与激发波长密切相关.     

Highly Sensitive Silver Nanorod Arrays for Rapid Surface Enhanced Raman Scattering Detection of Acetamiprid Pesticides

The determination of pesticide residue on agricultural products is increasingly important.Exposure to pesticides can cause severe acute reactions in humans, including aplastic anemia and leukemia.In this work, we developed a rapid and sensitive method to detect acetamiprid pesticide residue based on surface-enhanced Raman scattering.Silver nanorod (AgNR) arrays were fabricated by oblique angle deposition technology and were used as SERS substrates.Prior to detection, the AgNR arrays were cleaned with nitric acid solution or a mixture of methanol and acetone.Compared to the unwashed AgNR arrays, the AgNR arrays washed with methanol and acetone shows a signal enhancement 1000 times greater than the unwashed AgNR array due to the effective removal of the impurities on its surface.The limit of detection of acetamiprid was determined to be 0.05 mg/L.In addition, the molecular structure of acetamiprid was simulated and the corresponding vibration modes of the characteristic bands of acetamiprid were calculated by density function theory.To demonstrate its practical application, the AgNRs array substrates were applied successfully to the rapid identification of acetamiprid residue on a cucumber's surface.These results confirmed possibility of utilizing the AgNRs SERS substrates as a new method for highly sensitive pesticide residue detection.     

基于Au/SiO2纳米粒子的结晶紫表面增强拉曼特性研究

采用自组装-化学镀法制备了以SiO2为核,Au为壳层的核壳结构纳米粒子(Au/SiO2),以生物染色剂结晶紫为探针分子,研究了Au/SiO2的表面增强拉曼散射(SERS)效应,并考察了Cl-对SERS增强效应的影响。实验表明,Cl-对SERS有明显的增强效果,这主要是由于Cl-的加入使得Au/SiO2发生团聚,产生大量"热点",从而使SERS增强效果进一步加强。以Au/SiO2(5×1010 mL-1)为活性基底,KCl(0.01 mol/L)为额外增强剂,在水溶液中实现了对结晶紫(CV)的痕量检出,最低检测浓度可达到5×10-10mol/L。     

Surface-enhanced Raman scattering on mercaptopyridine-capped CdS microclusters

We obtained the high-quality Raman spectra of 4-mercaptopyridine (4-Mpy) adsorbed on CdS microclusters. The Raman signals were enhanced relative to the same molecules in solution. We compared the Raman spectra of 4-Mpy molecules adsorbed on CdS microclusters and Ag substrate. The difference of 4-Mpy molecules adsorbed on semiconductor and metal substrate was revealed. The results demonstrated that adsorbed species on semiconductor CdS can be detected by SERS spectroscopy.     

Surface-enhanced Raman scattering detection of cholinesterase inhibitors

A new sensitive surface-enhanced Raman scattering (SERS) assay for detection of cholinesterase inhibitors such as organophosphorous pesticides using silver colloidal nanoparticles was developed and optimized. Acetylcholinesterase (AChE) mediated the hydrolysis of acetylthiocholine to produce thiocholine, which interacted with the silver nanoparticles to give a specific SERS spectrum. Variation in enzyme activity due to inhibition was measured from changes in intensity of a characteristic peak (772 cm⁻¹) of the SERS spectrum that was directly correlated with the concentration of produced thiocholine. The method was demonstrated for the detection of paraoxon as reference AChE inhibitor. Limit of detection of paraoxon for 5 min incubation at 25 °C was 1.8 × 10⁻⁸ M. This assay can be utilized for the detection of trace amounts of any AChE inhibitor.     

One-pot synthesis of silver colloid with body-heat for surface-enhanced Raman spectroscopy detections

In this study, a convenient method of preparing the substrate is proposed with one-pot synthesis of silver colloid under body heat, and the SERS detection uses the fresh substrate to avoid the drawback of substrates' short life of use. The synthesis of silver colloid is carried out in a 10 mL vial by using ascorbic acid as a reductant and trisodium citrate as a stabilizer. The vial is grasped with the palm of the experimenter for several minutes without shaking. The proposed method is simple, rapid, green energy and cost-effective. By adjusting the concentration of trisodium citrate, not only the particle size can be controlled from about 110 nm to 50 nm but also the homogeneity of nanoparticles can be improved. As a SERS substrate, the silver colloid has high batch reproducibility and showed good SERS activity. The relative standard deviation between different manufacturers is 5.51% when the substrate of silver colloid is used for the detection of rhodamine 6 G. Using the substrate, the lowest detection concentrations of rhodamine 6 G, crystal violet, enrofloxacin, melamine and leucomalachite green are 1.0×10~(-8), 6.1×10~(-8),1.4 × 10~(-6), 7.1 ×10~(-5) and 5.1 ×10~(-8) mol/L, respectively. Results demonstrate that the developed method has the advantage of convenience and high efficiency in the field preparation of reliable SERS substrate.     

Surface-enhanced femtosecond CARS spectroscopy (SE-CARS) on pyridine

Surface-enhanced Raman scattering (SERS) has become an integral part of spectroscopy. The inelastic scattering process is enhanced by several orders of magnitude when molecules are in close contact to nano-structured coin metals. However, the use of surface enhancement in combination with nonlinear spectroscopy is by far not as common as in linear spectroscopy even though a more drastic effect could be expected. In our work, we report the observations we made from the preliminary studies on surface enhancement mechanisms in combination with coherent anti-Stokes Raman scattering (CARS) using femtosecond laser pulses. Silver colloids were used as enhancement medium. Molecules, which show conventional SERS were selected for the experiments. Femtosecond CARS was performed on these molecular systems in the presence and absence of silver colloids. The scattered CARS signal was collected both in the forward and sideward directions. From the analysis of the results general observations were made about the factors affecting the performance of SE-CARS.     

树枝状银微纳结构的表面增强拉曼散射效应研究

利用两电极电化学沉积法制备出一种树枝状银微纳结构基体.扫描电子显微镜(SEM)的表征结果证实所制备的银基体呈现出完整的树枝状结构,具有对称性的树枝和树干,且树叶清晰可见.实验结果表明,树枝状银微纳结构的表面增强拉曼散射(Surface-enhanced Raman scattering,SERS)可以检测到超低浓度的罗丹明6G(Rhodamine 6G,R6G,10-10 mol/L)光谱信号,即树枝状银微纳结构作为SERS基体表现出较好的灵敏性;当R6G的浓度在10-5~10-10 mol/L范围依次降低一个数量级时,谱带610 cm-1处的拉曼散射强度的相对标准偏差分别为12.1%,12.0%,11.7%,10.9%,13.2%和14.3%,表明所制备银基体的SERS"热点"(Hot spots)分布较均一,树枝状银微纳结构作为SERS基体具有较好的重现性;当低SERS活性的3-巯基丙酸(3-Mercaptopropionic acid,3MPA)的检测浓度为10-5 mol/L时,利用树枝状银基体能检测到3MPA的SERS光谱,说明所制备的银基体对低活性物质也具有较好的SERS灵敏性.     

Surface-enhanced Raman spectroscopy: benefits,trade-offs and future developments

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique with sensitivity down to the single molecule level that provides fine molecular fingerprints, allowing for direct identification of target analytes. Extensive theoretical and experimental research, together with continuous development of nanotechnology, has significantly broadened the scope of SERS and made it a hot research field in chemistry, physics, materials, biomedicine, and so on. However, SERS has not been developed into a routine analytical technique, and continuous efforts have been made to address the problems preventing its real-world application. The present minireview focuses on analyzing current and potential strategies to tackle problems and realize the SERS performance necessary for translation to practical applications.

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique with sensitivity down to the single molecule level that provides fine molecular fingerprints, allowing for direct identification of target analytes.     

双螺旋DNA在银和金电极上的现场付立叶表面增强拉曼光谱

采用Ｎｄ－ＹＡＧ激发器作激光光源的付立叶拉曼系统，研究了双螺旋ＤＮＡｄ（ＡＧ）８．ｄ（ＣＴ）８在银和金电极表面上的现场表面增强拉曼散射效应。结果发现在银电极表面上，该双螺肇ＤＮＡ出现ＳＥＲＳ信号的时间效应依赖于电极电势的大小。但是，高质量的ＳＥＲＳ谱表面无论在银或金电极表面上，该双螺旋ＤＮＡ均发生部分变性，而且还观察到该ＤＮＡ分子的ＳＥＲＳ谱随电极电势的变化而变化的现象。     

Surface-enhanced Raman scattering of 4-aminobenzenethiol on silver nanoparticles substrate

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.     

Surface-enhanced Raman spectra of pyridine and pyrazolide on silver colloids: chemical and electromagnetic effects

The surface-enhanced Raman spectra of pyridine and pyrazolide adsorbed on silver colloids are discussed with the help of a density functional theory calculation, based on a mixed functional. The ligand–surface interaction is modelled as an adduct of pyridine and pyrazolide with a single Ag atom or with a small Ag cluster. It is found that the model adduct satisfactorily reproduces the relative Raman intensities of adsorbed pyridine, while the same is not the case for pyrazolide. From the analysis of the excitation profiles the observed behaviour is correlated with the relative importance of the chemical and electromagnetic effects.Acknowledgementsensp;The authors gratefully thank the Italian Ministero dellIstruzione, Universita e Ricerca and the Consiglio Nazionale delle Ricerche for financial support to the Progetto Finalizzato Materiali Speciali II.Contribution to the Jacopo Tomasi Honorary Issue     

银纳米粒子在云母表面的二维组装及其表面增强拉曼效应

随着纳米技术的迅速发展 ,利用共价或非共价键作用将金属纳米粒子组装到固体基片上 ,因其方法简单、重复性好而成为研究热点 .目前 ,人们已经成功地利用带有— SH[1,2 ] ,—CN,— NH2 [3 ] 等基团的单层或多层膜作为偶联剂将 Au和 Ag等金属纳米粒子固定在玻璃、石英、硅、金等固体基片上 .但在许多情况下 ,偶联剂却成为一种干扰物质 .云母是一种重要的电子工业材料 ,并具有廉价、较易获得新鲜表面等特点 ,研究金属纳米粒子在云母表面的组装和排列无疑具有重要意义 .但是 ,迄今为止 ,在表面没有偶联剂修饰的条件下 ,以云母为基底的金属纳…     

Surface-enhanced Raman spectroscopy of water: Iniplications of the electromagnetic model

The electromagnetic model of surface-enhanced Raman scattering is used to show that in colloidal sols the failure to observe enhanced Raman signals from adsorbed water or even from a macroscopic layer of water near the surface is due not only to the small Raman cross section of water and the fact that any such enhanced signal is overwhelmed by that from the bulk water, but also because of the high wave number of the vibrational mode of water.