Adsorption Geometry of 4-Cyanopyridine on Ag Electrode by SERS

The adsorption of 4-cyanopyridine (PyCN) on Ag electrode has been studied by surface-enhanced Raman scattering. The Raman band of the CN group is at 2240 or 2100 cm^?1; it appears in various ranges of potential. When a series of potentials was applied stepwise to the electrode, the growing and vanishing of both bands was monitored by an optical multichannel analyzer with a time resolution 1 s or less. Some information about the kinetics of the adsorption and desorption of CN group and about the adsorption geometry of PyCN on the electrode was obtained.     

密度泛函理论研究银上吸附对巯基吡啶的SERS化学增强效应

基于密度泛函理论计算和拉曼光谱理论分析,我们研究了对巯基吡啶(4MPY)分子的拉曼光谱和其在银上的表面增强拉曼光谱(SERS),并进一步探讨了SERS与界面吸附结构、异构化、质子化和氢键作用以及低能激发态的关系。首先,我们对两种分子异构体的相对稳定性和拉曼光谱进行了理论分析。在此基础上,进而研究了该分子与不同银簇作用时的拉曼光谱,结果表明,4MPY以巯基硫与银簇作用形成强的Ag―S键,导致拉曼光谱的线型不依赖于所选银簇的大小。接着我们考虑了吡啶氮端作用的两种情况。(1)当4MPY-银簇复合物同时以吡啶氮与水簇或水合质子簇形成氢键时,结果表明吡啶环的部分振动频率随氢键和质子化发生蓝移。(2)当考虑吡啶氮与银簇作用时,吡啶环三角畸变振动发生蓝移。上述情况不仅解释了实验观测的振动频率变化,而且表明了化学环境改变对相对拉曼强度的影响。最后,我们计算了当对巯基吡啶分子以单端或双端与银簇作用,在考虑激发光与低能激发态的能量匹配时,拉曼光谱强度与低能激发态的关系。计算结果表明,在双端吸附构型下,与吡啶氮成键的银簇受激发产生电荷转移态,不仅导致吡啶环v_(12)、v_1和v_(8a)振动的拉曼信号增强,而且选择性地增强吡啶环C―H面内对称弯曲振动v9a的拉曼信号。     

花状银微纳米结构的合成及SERS性质

通过简便的水溶液方法制备出一种新颖的由纳米片组成的花状银微纳米结构, 采用XRD, SEM, TEM, HRTEM和SAED等手段进行了表征. 考察了反应体系pH值对产物形貌的影响, 并对花状银微纳米结构的形成机理进行了初步探讨. 所制得的微纳米结构由许多纵横交错的纳米片组成. 实验结果表明, 制备的银微纳米结构作为表面增强拉曼散射(Surface-enhanced Raman Scattering, SERS)的基底具有很强的活性.     

SERS study of the interaction of thiourea with a copper electrode in sulphuric acid solution

The electrochemical interaction of thiourea with a copper electrode in sulphuric acid solution was investigated using Fourier transform Raman and in situ surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra of thiourea at a copper electrode were obtained in solutions containing greater than 5 ppm thiourea; the spectra obtained were consistent with adsorption of the molecule on the copper electrode via the sulphur atom. The SERS spectra provide evidence of complex formation involving thiourea and sulphate species at the electrode surface.     

Facile Synthesis of C3N4/Ag Composite Nanosheets as SERS Substrate for Monitoring the Catalytic Degradation of Methylene Blue

The C₃N₄/Ag composite nanosheets were facilely prepared via an in situ reduction processand Ag nanoparticles were well dispersed on the surface of C₃N₄ nanosheets. The unique two-dimensional structure and strong interactions between C₃N₄ nanosheetsand Ag nanoparticles contributed the good surface-enhanced Raman scattering(SERS) property due to the electromagnetic field enhancement. In addition, the as-prepared C₃N₄/Ag composite nanosheets could be used as catalysts or photocatalyst for the degradation of methylene blue(MB) in the presence of NaBH₄ or under visible light. Therefore, a facile SERS monitoring of the catalytic and photocatalytic degradation process of MB and the determination of the reaction kinetics were developed.     

过渡金属表面α-吡啶基的振动光谱学判据

基于簇模型采用密度泛函理论在B3LYP/6-311+G^**/LANL2DZ(metal)基组水平上计算了吡啶及α-吡啶基吸附于Pt、Pd、Rh、Ni四种金属表面的红外和拉曼光谱. 通过详细地分析和比较计算结果与文献报道的实验谱图, 提出了以N端吸附的吡啶分子和α-吡啶基这两种表面物种各自存在的谱学判据. 计算结果表明在以上四种金属表面, α-吡啶基的拉曼活性比吡啶的小, 而特征谱峰的红外强度与吡啶相当. 该结果表明红外光谱是检测金属表面α-吡啶基的有效手段, 也解释了采用表面增强拉曼光谱和红外光谱研究吡啶吸附在金属表面得出不同结构的原因.     

Bifunctional AgCl/Ag composites for SERS monitoring and low temperature visible light photocatalysis degradation of pollutant

With the assistance of Polyvinylpyrrolidone (PVP), AgCl/Ag composites were fabricated in N, N-Dimethylformamide (DMF) solvent via a photoactivated route. The size of AgCl particles was in the range of 500 nm to 1 μm and the Ag particle's diameter was about 10–20 nm. Different from those core–shell structures reported before, the Ag nanoparticles were dispersed uniformly both on the surface and in the body of AgCl particles. The generation of such kind of composites was resulted from the reducing ability of DMF and light irradiation during the formation of AgCl particles. The as-obtained AgCl/Ag composites presented great activity for both surface-enhanced Raman scattering (SERS) detection and visible light photocatalytic degradation of organic dyes. Additionally, the AgCl/Ag composites could maintain high photocatalytic activity even though the ambient temperature was as low as 15 °C and recycle photocatalysis experiments indicated that the photocatalyst exhibited higher stability. Such kind of AgCl/Ag composites holds great potential for environmental monitoring devices and pollutant treatments.     

Optical fibre SERS sensors

Surface-enhanced Raman scattering (SERS) has established itself as an important analytical technique. However, efforts to transfer the technology from the laboratory to the production line, clinic or field have been frustrated by the lack of robust affordable substrates and the complexity of interfacing between sample and spectrometer. Prompted by the success of optical fibre systems for implementing normal Raman scattering spectroscopy in remote locations and biomedical applications, attention has now shifted to the development of SERS-active optical fibres. Other workers have attempted to develop SERS probes with extended interaction lengths and both far-field and near-field SERS imaging techniques for high-resolution chemical mapping of surfaces. This review discusses the development of these technologies and presents the current state of the art. Although recent developments show great promise, some outstanding challenges and opportunities remain to be addressed.     

SnO2纳米粒子作为SERS基底的研究

采用溶胶-水热法制备了不同尺寸的SnO2纳米粒子, 并将其作为表面增强拉曼散射(Surface-enhanced Raman scattering, SERS)活性基底, 重点探讨了表面缺陷能级与SERS性能的关系. 观察到4-巯基苯甲酸(4-MBA)吸附在150 ℃水热合成的SnO2纳米粒子上的SERS 信号最强, 随着在空气中煅烧温度的升高, SERS信号逐渐减弱. 分别用透射电子显微镜、 紫外-可见光谱、 荧光光谱、 X射线衍射和X射线光电子能谱对SnO2纳米粒子进行了表征. 结果表明, SnO2纳米粒子的表面氧空位和缺陷等表面性质在增强拉曼散射性能中发挥着重要的作用, 表面氧空位和缺陷等含量越高其SERS信号就越强.     

银纳米枝的合成及表面增强拉曼效应

利用硝酸银与铜之间发生置换反应原理, 在铜箔上得到了有序的银纳米枝结构, 用十二烷基磺酸钠(SDS)为表面活性剂, 通过调控前驱体硝酸银的浓度, 可在铜箔上得到不同密度的银纳米枝. 表面拉曼增强实验结果表明, 当分别以对巯基苯胺(4-ATP)、腺嘌呤和罗丹明G6为探针分子时, 有序的银纳米枝结构比无序的银纳米粒子具有更好的拉曼增强活性; 且随银纳米枝密度的增加, 表面拉曼增强活性有所提高. 该有序的银纳米枝结构是较好的表面增强拉曼(SERS)活性基底, 在有机分子和生物分子的SERS检测方面将具有一定的应用前景.     

理论研究Ag/MPH/TiO2体系的SERS光谱化学增强机理

采用密度泛函理论研究了Ag/对巯基苯酚(MPH)/TiO₂体系的表面增强拉曼散射(SERS)光谱化学增强机理. 分别研究了Ag₁₃/MPH和Ag₁₃/MPH/TiO₂复合物在514.5 nm激发波长下的拉曼光谱, 发现由于TiO₂的引入, 发生了非完全对称振动模式峰选择性增强的现象. 通过对电荷转移复合物基态和激发态的指认, 发现当激发波长大于MPH-TiO₂电荷转移复合物的光学吸收阈值(635 nm)时, 该体系内将发生从Ag到MPH-TiO₂部分的光诱导电荷转移现象. SERS光谱中b₂模式的选择性增强, 来源于相应振动模式与电荷转移跃迁的耦合(Herzberg-Teller机制). 我们的理论结果不仅支持了实验现象, 并且明确界定了电荷转移复合物, 对于该体系存在的光依赖SERS现象提供了一个清晰的理论阐述.     

Theoretical Investigation on SERS of Pyridine Adsorbed on Cn Clusters Induced by Charge Transfer: A Hint that SERS Could be Applied on Many Materials

The SERS spectra of pyridine–C_n (n=1–6) complexes are investigated theoretically. The obtained enhancement factors of about 10²–10³ in the pre‐resonance Raman spectrum calculations are attributed to charge‐transfer transitions from the carbon clusters to pyridine, where a good match of band structures between substrates and probe molecules is essential.     

Surface-enhanced Raman scattering (SERS) for probing internal cellular structure and dynamics

Surface-enhanced Raman scattering (SERS) provides vibrational information about molecules that are located within several nanometers of the surface of a metallic nanoparticle. This review describes the various challenges and successes of applying SERS inside living cells in order to gain information about the internal structure and dynamic processes occurring in the intracellular matrix. In particular, the challenges associated with the introduction of metal nanoparticles into cells are described, as well as the complexity of interpreting SERS spectra from within complex biological environments. Strategies for understanding and improving the specificity of SERS in vivo are also presented.

Synthesis of size tunable monodispersed silver nanoparticles and the effect of size on SERS enhancement

Spherical and monodispersed silver nanoparticles (AgNPs) are ideal for fundamental research as the contribution from size and shape can be accounted for in the experimental design. In this paper a seeded growth method is presented, whereby varying the concentration of sodium borohydride-reduced silver nanoparticle seeds, different sizes of stable spherical nanoparticles with a low polydispersity nanoparticles are produced using hydroquinone as a selective reducing agent. The surface-enhanced Raman scattering (SERS) enhancement factor for each nanoparticle size produced (17, 26, 50, and 65 nm) was then assessed using three different analytes, rhodamine 6G (R6G), malachite green oxalate (MGO) and thiophenol (TP). The enhancement factor gives an indication of the Raman enhancement effect by the nanoparticle. Using non-aggregated conditions and two different laser excitation wavelength (633 nm and 785 nm) it is shown that an increase in particle size results in an increased enhancement for each analyte used.     

钯纳米颗粒形貌控制合成及其SPR／SERS性质

在水溶液中分别以十六烷基三甲基溴化铵（CTAB）和CTAB／柠檬酸钠混合剂为包覆剂合成钯纳米颗粒,并研究其形貌演变．钯纳米颗粒在成核阶段会形成具有不同孪晶结构的晶核,在生长阶段又会选择性的放大某一组晶面,这两个因素导致了钯纳米颗粒形貌的多样性．在合成中CTAB既会影响钯纳米颗粒的成核,也会影响颗粒晶面的选择性生长．通过改变CTAB和还原剂的量可以调控钯纳米颗粒的形貌．溶液中CTAB和还原剂浓度的改变,非常明显地影响合成产物中不同形貌钯纳米颗粒的产率．通过向溶液中引入柠檬酸离子调控纳米颗粒的成核与生长过程,首次合成出了星状钯二十面体和截面为五角星形的钯纳米棒．这些不同形貌的钯纳米颗粒有着不同的表面等离子体共振和表面增强拉曼散射性质．     

胞嘧啶吸附在粗糙金电极上的表面增强拉曼光谱

应用电化学伏安法和表面增强拉曼光谱(SERS)研究在-1.0 V~0 V电位区间内胞嘧啶于粗糙金电极表面的吸附行为.结果表明,在本实验的电位区间,胞嘧啶是以其N3位垂直吸附在粗糙金电极表面的.在负电位区间环呼吸振动模的强度出现极大值,与其它振动模强度相比,作者认为电磁场的增强和电荷转移均使该谱峰的拉曼信号增强.胞嘧啶的环呼吸振动频率随着电位负移而红移,这意味着它与金电极的成键作用减弱.同时也表明SERS谱可用于研究生物分子在金属电极表面的吸附行为.     

Highly sensitive SERS monitoring of catalytic reaction by bifunctional Ag-Pd triangular nanoplates

Surface-enhanced Raman spectroscopy (SERS) can attain the “fingerprint” information of molecules from their vibrational transitions for detecting chemical species and thus displays extraordinary application value in studying chemical reaction mechanism catalyzed by noble metal nanoparticles in recent years. Herein, we successfully fabricated bifunctional Ag-Pd triangular nanoplates with integration of catalytic and SERS activities, using Ag triangular nanoplates as templates and Na₂PdCl₄ as Pd precursor in the presence of ascorbic acid acting as reducing agent and polyvinylpyrrolidone serving as stabilizing agent. We found slowly titrating Na₂PdCl₄ solution, compared with the one-shot injection during reaction, can strongly restrain the galvanic replacement reaction and maintain the Ag content, therefore retaining the plasmonic and SERS properties of Ag-Pd triangular nanoplates. By easily adjusting the amount of Na₂PdCl₄, we can optimize the SERS and catalytic activities of Ag-Pd triangular nanoplates. The optimal Ag-Pd triangular nanoplates with dual functionalities are used to follow the catalytic reduction process of 4-nitrothiophenol in the presence of NaBH₄ by SERS. The results reveal 4-nitrothiophenol is directly transformed to 4-aminothiophenol through a one-step route. Thereby, the prepared Ag-Pd triangular nanoplates are effective and suitable for sensitively investigating the catalytic reaction process by in situ SERS.     

单壁碳纳米管在不同材质基片银膜上的表面增强拉曼光谱

在玻璃、白宝石和石英基片上,利用化学沉积法和溶胶法制备了纳米结构活性银膜,系统地研究了两种不同方法制备的单壁碳纳米管(SWNT)的表面增强拉曼光谱(SERS)的G带和D带.同一样品的G带,在不同基片上的峰移量不同,在白宝石基片上移动更大,峰强更高,可以更敏感地反映SERS效应.D带的峰形随基片不同而改变.金属性管的含量较高的样品,其D带光谱的峰移较半导体性管含量较高的样品更显著,表明金属性碳纳米管与SERS活性银膜的界面相互作用更强.     

苯在铑电极上吸附的表面增强拉曼散射光谱研究

利用成熟的电极处理方法成功地获得了苯在粗糙铑电极上电化学吸附的拉曼谱图.详细探讨了电极电位、电解质等因素对苯的电化学吸附的影响.结果表明,苯分子吸附到粗糙铑电极上后,表面拉曼谱图与纯苯本体谱图的差别很大,说明吸附后的苯分子在几何及电子结构上发生了巨大变化.苯分子可能以1,3-环己二烯的结构吸附于铑电极表面.     

利用壳层厚度调节核壳Au@Pd纳米粒子的SERS活性

设计合成了一种尺寸可控, 且外壳上无“针孔”的核壳钯包金(Au@Pd)纳米粒子, 通过改变核的尺寸和外壳的厚度来调控其光学性质, 并用TEM、HRTEM、UV-Vis和SERS等手段对其进行了表征. 通过研究Au@Pd纳米粒子的SERS活性随Pd壳层厚度变化的规律, 发现薄壳Au@Pd纳米粒子远远优于Pd金属本身的SERS活性, 其原因主要是内层金核电磁场增强的长程效应.