Adsorption and reduction reactions of anthraquinone derivatives on gold electrodes studied with electrochemical surface‐enhanced Raman spectroscopy

Electrochemical surface‐enhanced Raman spectroscopy (EC‐SERS), combined with cyclic voltammetry, and the density functional theoretical (DFT) method were used to investigate self‐assembled monolayer (SAM) adsorption and reduction processes. Here, we choose the system of interest, being thiolacetyl‐terminated 2‐phenylene ethynylene‐substituted anthraquinone molecule (2‐AQ) on gold electrodes in buffered aqueous and aprotic solutions. In the buffered aqueous solution, the results of cyclic voltammetry and EC‐SERS measurements, as well as DFT calculations, indicate that the adsorbed molecules pass through a two‐electron two‐proton reduction reaction with cathodic polarization. In particular, the latter two methods confirmed the structural changes of SAMs during the process of redox reaction, 2‐AQ + 2e + 2H⁺ → 2‐AQH₂, where 2‐AQ and 2‐AQH₂ are the oxidized and reduced forms, respectively. In aprotic solutions (acetonitile), a stepwise reaction mechanism was proposed on the basis of the results of EC‐SERS and DFT calculations. The first reduction peak should be a half reaction process 2‐AQ + e → 2‐AQ⁻, where 2‐AQ⁻ is a single electron reduced form. Compared with that of 2‐AQ SAMs in the buffered aqueous solution, the results of EC‐SERS and DFT calculations in aprotic solution suggested that the solvent effect significantly influences the redox process of 2‐AQ in electrochemical interfaces. Copyright © 2012 John Wiley & Sons, Ltd.     

表面增强拉曼光谱和电化学方法研究中性条件下咪唑对镍电极的缓蚀作用

利用表面增强拉曼光谱技术(SERS)研究了咪唑在镍电极表面的吸附机理和吸附方式,并分别比较了镍电极在加入咪唑前后溶液中的循环伏安曲线和极化曲线,计算了其缓蚀效率。结果表明,在镍电极表面,咪唑起到了较好的缓蚀效果;在研究电位区间内所得的SERS谱图中,面内振动峰占据了主导地位,咪唑是以垂直略带倾斜的方式吸附在镍电极表面的;而N—H面内弯曲振动峰(1 173 cm-1)的出现和pH值接近中性的研究体系证明了咪唑是以中性咪唑分子的形式存在;低波数区N—Ni伸缩振动峰(214 cm-1)的出现进一步验证了咪唑通过N原子与镍电极表面略带倾斜的吸附方式。     

Surface enhanced Raman scattering of organic sample powders spread over vacuum-evaporated silver thin film

Surface enhanced Raman scattering (SERS) from samples prepared by spreading para-nitrobenzoic acid (PNBA) and adenosine powders over silver thin films was achieved. The SERS intensities of the ionized PNBA on the silver film increase with increased applied pressure through a cover-glass and reach a maximum at 0.6 MPa. In contrast, the signals caused by adenosine remain nearly unchanged under applied pressures of 0-0.6 MPa. Beyond 0.6 MPa, the signals attributable to samples decrease in intensity. Atomic force microprobe images reveal that nanometer-scale surface morphology is changed by 0.8 MPa pressure, suggesting that the decrease in SERS intensity is related to pressure-induced morphological changes. Results obtained in this study indicate that SERS spectra are obtainable easily, without solvents, under ambient conditions using dispersion of the sample powder.     

银颗粒表面尿嘧啶分子的SERS实验研究——KCl对尿嘧啶分子吸附状态的影响

利用表面增强喇曼散射(SERS)在灰银胶体系中研究了KCl对尿嘧啶分子吸附状态的影响,并将实验结果与Oh等人在黄银胶体系中的实验结果进行了详细比较.对这一实验现象进行了定性解释.     

A surface-enhanced Raman scattering study of CTAB adsorption on copper

Surface-enhanced Raman spectroscopy (SERS) has been used to study, in situ, the adsorption of cetyltrimethylammonium bromide (CTAB) on copper. The data obtained allow the determination of CTAB's adsorption rate from aqueous solution and are consistent with physisorption or weak chemisorption via the quaternary ammonium group. The use of “surface selection rules” to derive orientation information is examined.     

对硝基苯甲酸在水溶液和银胶中的紫外拉曼光谱(英文)

本文给出了紫外激发下的PNBA水溶液的拉曼光谱图,并对图中峰位做了相应的归属认证。本文还报道了PNBA在银胶中的表面非增强拉曼散射现象,并分析了导致该现象可能的原因     

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.     

咪唑在银电极上吸附行为的SERS研究

咪唑在银电极上吸附行为的ＳＥＲＳ研究徐知三，张传飞，旷富贵，王小华，刘海林（武汉大学分析测试中心武汉４３００１２）（武汉大学环境科学系武汉４３００７２）ＳｔｕｄｙｏｎＴｈｅＡｄｓｏｔｐｔｉｏｎＢｅｈａｖｉｏｕｒｏｆＩｍｉｄａｚｏｌｅｏｎＳｉｌｖｅｒＥ...     

非水体系中吡啶和乙腈在铂电极上竞争吸附的表面增强拉曼光谱研究

继非水体系中CO在过渡金属表面吸附的表面增强拉曼光谱（SERS）研究之后，本文是又一篇关于非水体系中过渡金属表面SERS研究的文章。从拉曼谱峰的变化结果发现，吡啶在Pt电极表面是强烈的化学吸附，并且由于其吸附的量和吸附取向随电位在不断地变化，与水体系中吡啶（Py)在Pt电极表面的吸附相比较，SERS谱峰除了强度较低之外，在可研究的电位区间、谱峰位置以及其随电位变化等方面都存在着不同，这缘于结构较为复杂的有机溶剂分子在电极表面组成了更为复杂的界面结构，造成固／液界面的电迁移等电极动力学过程发生了变化，为了说明这一现象，文中还采用强吸附离子I^-进行研究，得到相似的结果。     

DFT study and quantitative detection by surface‐enhanced Raman scattering (SERS) of ethyl carbamate

Ethyl carbamate (EC), a potentially toxic compound, is found in alcoholic beverages and fermented foodstuff. A combined experimental and theoretical study of Raman on EC is reported in this work for the first time. The Raman bands observed for EC in solid phase are characteristic for the carbonyl group, C―C, C―H and N―H stretching and deformation vibrations. These spectral features coupled with a pKa study allowed establishing the neutral species of EC present in the aqueous solutions experimentally tested at different concentrations. In addition, by performing a density functional theory study in the gas phase, the calculated geometry, the harmonic vibrational modes, and the Raman scattering activities of EC were found to be in good agreement with our experimental data and helped establish the surface‐enhanced Raman scattering (SERS) behavior and EC adsorption geometry on the silver surfaces. The Raman peak at 1006 cm⁻¹, assigned to the υ_s(CC) + ω(CH) modes, the strongest and best reproducible peak in the SERS spectra, was used for a quantitative evaluation of EC. The limit of detection, which corresponds to a signal‐to‐noise ratio equal to 3, was found to be 2 × 10⁻⁷ M (17.8 µg l⁻¹). SERS spectra obtained by using hydroxylamine hydrochloride‐reduced silver nanoparticles provide a fast and reproducible qualitative and quantitative determination of EC in aqueous solution. Copyright © 2013 John Wiley & Sons, Ltd.     

乙醇相银溶胶中2—氨基苯并咪唑的SERS光谱研究

由于水相中拉曼谱带强度测定困难,本文利用乙醇883.8cm~(-1)作内标,研究了乙醇相银溶胶中SERS峰强与浓度的关系,发现随着2-氨基苯并咪唑浓度的改变,SERS峰强并不与浓度成正比,不同浓度溶液中1237cm~(-1)面内振动的改变显示了2-氨基苯并咪唑吸附取向的变化。     

Potential‐induced Raman behavior of individual (R)‐di‐2‐naphthylprolinol molecules on a Ag‐modified Ag electrode

The applicability of surface‐enhanced Raman spectroscopy is demonstrated to probe the adsorption behavior of individual molecules on a Ag electrode. High‐quality SERS spectra of (R)‐di‐2‐naphthylprolinol (DNP) were obtained from ultradilute solutions (10⁻¹² M ) on the Ag‐nanoparticle‐modified Ag electrode, which is attributed to the high electromagnetic (EM) effect of the SERS‐active system as well as to the strong adsorption and interaction of DNP molecules with Ag. The stable SERS spectra present remarkable potential dependence, which gives evidence for the behavior of individual DNP molecules on the Ag surface. Based on statistical analysis for the probability of DNP molecules located in ‘hot spots’, we propose an SERS mechanism for individual molecules in the electrode system, in combination with the hot‐spot model and orientation of the probe molecules. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering study of human serum on PVA?Ag nanofilm prepared by using electrostatic self‐assembly

Polyvinyl alcohol (PVA)‐protected silver nanoarchitecture (PVA Ag nanofilm) on the surface of the glass substrate was prepared by using electrostatic self‐assembly at a proper voltage. The two‐dimensional morphology of the PVA Ag nanofilm has been examined by scanning electron microscopy (SEM). The surface‐enhanced Raman scattering (SERS) spectra of human serum (HS) on PVA Ag nanofilms were recorded. The results show that the Raman scattering of HS can be enhanced efficiently based on these PVA Ag nanofilms. However, it also can be seen that the effect of sodium citrate (SC) acting as anticoagulant on the SERS spectrum of HS is unnegligible, which has not been discussed adequately in the previous reports. To discuss the effect of SC on the SERS spectrum of HS, we have studied the normal Raman spectra of solid SC and the SERS spectra of 1.0 × 10⁻³ mol/l aqueous solution of SC adsorbed on the PVA–Ag nanofilms. Meanwhile, Raman wavenumbers of the SC molecule were calculated by using the method of DFT‐B3LYP/6‐31G*, and the dominant assignations of the calculated wavenumbers were performed. It was found that the density functional theory (DFT) calculation of SC Raman spectrum matches well with the experimental results. With the perfect reproducibility and high SERS activity, this method will be useful in the development of HS detection methods. Copyright © 2010 John Wiley & Sons, Ltd.     

CTAB对四-(4-N-甲基吡啶)卟啉SERS谱的影响

研究了阳离子表面活性剂十六烷基三甲基溴化铵 (CTAB)对四 ( 4 N 甲基吡啶 )卟啉 (H2 TMPyP)及其银配合物 (AgTMPyP)在Ag胶中的表面增强拉曼散射 (SERS)谱的影响 .SERS光谱表明 ,吸附于Ag胶粒的H2 TMPyP与衬底银原子结合形成AgTMPyP ,加入CTAB后 ,部分AgTMPyP表面络合物还原为H2 TMPyP .相似的去金属化反应也出现在AgTMPyP/Ag胶 /CTAB体系中 .CTAB的加入使SERS谱带强度明显增加 .AgTMPyP的去金属化被认为是由于CTAB的存在使Ag胶颗粒表面附近微环境发生改变     

Surface‐enhanced Raman scattering sensing on black silicon

Reactive ion etching was used to fabricate black‐Si over the entire surface area of 4‐inch Si wafers. After 20 min of the plasma treatment, surface reflection well below 2% was achieved over the 300–1000 nm spectral range. The spikes of the black‐Si substrates were coated by gold, resulting in an island film for surface‐enhanced Raman scattering (SERS) sensing. A detection limit of 1 × 10^?6 M (at count rate > 10² s^?1 . mW^?1) was achieved for rhodamine 6G in aqueous solution when drop cast onto a ～ 100‐nm‐thick Au coating. The sensitivity increases for thicker coatings. A mixed mobile‐on‐immobile platform for SERS sensing is introduced by using dog‐bone Au nanoparticles on the Au/black‐Si substrate. The SERS intensity shows a non‐linear dependence on the solid angle (numerical aperture of excitation/collection optics) for a thick gold coating that exhibits a 10 times higher enhancement. This shows promise for augmented sensitivity in SERS applications.     

Adsorption of 2‐amino‐5‐cyanopyridine on a gold surface as probed by surface‐enhanced Raman spectroscopy

The adsorption of 2‐amino‐5‐cyanopyridine (2‐ACP) was investigated in solution at different pH values by i n situ surface‐enhanced Raman scattering (SERS) spectroscopy combined with the electrochemical method. The assignments of the main bands were first performed on the basis of the spectral features of similar compounds and with the help of density functional theory calculations. The results revealed that the adsorption and the interfacial structure of 2‐ACP on the Au electrode depended on the applied potential and the pH values of the solution. In the natural solution, 2‐ACP was adsorbed on the surface with a vertical orientation by the CN group from − 0.4 to − 1.0 V, whereas in the − 0.4 to 0.8 V range, the N atom of the pyridine ring was bound to the surface. A transition region for the reorientation of the two adsorption modes was observed from − 0.8 to − 0.4 V. A flat configuration was preferred at an extremely negative potential. A similar surface adsorption behavior was observed in the alkali environment, while the Stark effect slope decreased because of the adsorption of OH⁻. Due to the protonation of N atom in the acidic solution, the potential region for the coexistence of two configurations ranged from − 0.4 to 0.2 V. Additionally, a similar adsorption configuration was proposed on the Au colloids at various pH values. The results revealed that the adsorption behavior became more complex on colloidal surfaces than that on a rigid electrode surface. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Enrichment of surfactant from its aqueous solution using ultrasonic atomization

Dilute aqueous solutions of dodecyl-benzenesulfonic acid sodium salt (DBS-Na) and polyoxyethylenenonylphenyl ethers (PONPEs) were ultrasonically atomized. The surfactants were concentrated in collected mist droplets. The enrichment ratio increased with decreasing surfactant concentration. Depending on the surfactant’s molecular weight and affinity to water, different enrichment ratio was observed in the range of low feed concentrations. For anionic surfactant, DBS-Na, the enrichment ratio was significantly improved by KCl addition and a peak appeared on the plot of the ratio against KCl concentration. Addition of NaCl or CaCl₂ · 2H₂O to the surfactant solution also enhanced the enrichment ratio; however, the effect was relatively small. Such behaviors of the ratio were interpreted as enhanced interfacial adsorption of the surfactant and a lack of supply of surfactant monomers from liquid bulk because of slow breaking of surfactant micelles. Time required for collecting an amount of mist was also observed. Among the three salt systems, the time for KCl system was twice as long as others. This fact suggested that the formation of smaller droplets in KCl system.     

关于氯离子对银胶体系SERS效应的进一步增强机理

在一些情况下添加氯离子能引起表面增强拉曼散射的进一步增强,本文提出了SERS效应中氯离子在银胶粒子和分子之间搭桥,从而促成吸附并引进一步增强的观点。设计了实验,验证了该观点的正确性。