Spectroscopic analysis of L-histidine adsorbed on gold and silver nanoparticle surfaces investigated by surface-enhanced Raman scattering

The adsorption of l-histidine on gold (Au) and silver (Ag) nanoparticle surfaces has been comparatively analyzed by means of surface-enhanced Raman scattering (SERS). The SERS spectra of l-histidine on Ag were found to be quite different from those on Au, indicating dissimilar adsorption structures depending on metal substrates. Most peaks of l-histidine on Ag appeared to be due to coordination via the carboxylate (COO(-)) group with an imidazole ring of fairly upright geometry, whereas on Au it was assumed to adsorb with a rather flat geometry. A density functional theory (DFT) calculation was performed at the level of B3LYP/LANL2DZ to estimate the energetic stability of the binding of the imidazole ring and the carboxylate group of l-histidine with the Ag and Au atoms, respectively. Based on the DFT calculation, the carboxylate group of l-histidine was predicted to bind more favorably to Ag than to Au, and this was in line with our SERS spectral analysis.     

Raman, surface enhanced Raman spectroscopy, and DFT calculations: a powerful approach for the identification and characterization of 5-fluorouracil anticarcinogenic drug species

The normal Raman and SERS spectra of 5-fluorouracil (5-FU) in water solution and attached to a biological artificial model (a silver colloid) at different pH values were recorded and discussed. The DFT calculation results helped us to establish for the first time the most stable resonance structure for each of the tautomeric forms (i.e., two enol and two enolate forms) and to interpret the Raman and SERS spectra. At alkaline pH, both deprotonated forms of 5-FU were found to be present in solution and to adsorb on the Ag surface in a perpendicular orientation or an orientation not significantly tilted from the surface normal. The N3-deprotonated form seems to be the dominant tautomer in the adsorbed state, more probably attached through the O7 atom. At acid pH values, the N3-deprotonated form was again found to be the mainly chemisorbed species adopting a similar orientation. The combination of these two approaches (i.e., the theoretical and experimental one) proved to be a viable candidate for inclusion in a rapid, sensitive biological method of detecting and studying such essential anticarcinogenic species or biological threats in different conditions.     

Surface enhanced Raman scattering investigation of the halide anion effect on the adsorption of 1,2,3-triazole on silver and gold colloidal nanoparticles

The halide anion effect on the adsorption of 1,2,3-triazole on Ag and Au colloidal nanoparticles has been investigated by means of surface enhanced Raman scattering (SERS), UV-visible absorption spectroscopy, and scanning electron microscopy. To interpret the SERS spectra, the vibrational spectra of 1,2,3-triazole were assigned with the help of density functional theoretical (DFT) calculations of the two tautomers of 1,2,3-triazole, both free and bound to Ag and Au adatoms. Upon addition of halide anions, both tautomers interact with the Ag surface through one nitrogen atom. Analogous behavior is observed in the case of basified Au colloids, whereas at the usual pH of these hydrosols (approximately 6) the adsorption of 1,2,3-triazole is the same of that observed in halide-free colloids.     

First Principles Calculations Toward Understanding SERS of 2,2′-Bipyridyl Adsorbed on Au,Ag, and Au–Ag Nanoalloy

First principles electrodyanmics and quantum chemical simulations are performed to gain insights into the underlying mechanisms of the surface enhanced Raman spectra of 22BPY adsorbed on pure Au and Ag as well as on Au–Ag alloy nanodiscs. Experimental SERS spectra from Au and Ag nanodiscs show similar peaks, whereas those from Au–Ag alloy reveal new spectral features. The physical enhancement factors due to surface nano-texture were considered by numerical FDTD simulations of light intensity distribution for the nano-textured Au, Ag, and Au–Ag alloy and compared with experimental results. For the chemical insights of the enhancement, the DFT calculations with the dispersion interaction were performed using Au₂₀, Ag₂₀, and Au₁₀Ag₁₀ clusters of a pyramidal structure for SERS modeling. Binding of 22BPY to the clusters was simulated by considering possible arrangements of vertex and planar physical as well as chemical adsorption models. The DFT results indicate that 22BPY prefers a coplanar adsorption on a (111) face with trans-conformation having close energy difference to cis-conformation. Binding to pure Au cluster is stronger than to pure Ag or Au–Ag alloy clusters and adsorption onto the alloy surface can deform the surface. The computed Raman spectra are compared with experimental data and assignments for pure Au and Ag models are well matching, indicating the need of dispersion interaction to reproduce strong Raman signal at around 800 cm^–1. This work provides insight into 3D character of SERS on nanorough surfaces due to different binding energies and bond length of nanoalloys. © 2018 Wiley Periodicals, Inc.     

Surface-enhanced Raman scattering and adsorption studies of morphine on silver island film

In this work, surface-enhanced Raman spectroscopy (SERS), infrared adsorption (IR), normal Raman (NR) scattering as well as density functional theory (DFT) computational methods have been employed to investigate the adsorption and orientation of morphine on silver surface. The structure of morphine and its vibrational spectra were determined at B3LYP/6-31G(d) level, and the results were used in the assignment of the vibrational spectra. The calculated data showed fairly good agreement with both corresponding experimentally observed spectra. These results, along with the application of surface selection rules of SERS, suggest that the molecules had a charge transfer adsorption on Ag island film and both planes of its ‘T’ type structure had a rather perpendicular orientation to the substrate mainly via the lone-pair electrons of the oxygens.     

Reversible adsorption change of 2‐amino‐4,5‐imidazoledicarbonitrile on Ag electrode surfaces by potential‐dependent surface‐enhanced Raman scattering

The potential‐induced adsorption change of 2‐amino‐4,5‐imidazoledicarbonitrile (AIDCN) on Ag electrode surfaces has been examined by surface‐enhanced Raman scattering (SERS) in an applied potential range between ?1.0 and 0.2 V. Upon adsorption, AIDCN has a substantial interaction with the Ag metal surfaces via its two nitrile groups. The CN stretching peaks at ～2200 cm^?1 appeared to be more intensified and redshifted at a negative potential. The deconvolution peak analysis of the CN bands at various voltages suggests that there should be a change in binding modes of AIDCN on Ag surfaces. This potential‐dependent orientation change appeared to be reversible. The density functional theory (DFT) calculation of AIDCN on Ag cluster atoms is used to explain its potential‐dependent adsorption. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface-enhanced Raman scattering of 4,4′-bipyridine on silver by density functional theory calculations

Surface-enhanced Raman scattering (SERS) of 4,4′-bipyridine (BPy) on silver foil substrate was measured using the 488, 514.5, and 1064 nm excitation lines. Density functional theory (DFT) methods were used to calculate the structure and vibrational spectra of Ag–BPy, Ag₃–BPy and Ag₄–BPy complexes with B3LYP/6-31++G(d,p)(C,H,N)/Lanl2dz(Ag) basis set. The Raman bands of BPy were assigned on the basis of the calculation of potential energy distribution. The calculated spectra of Ag–BPy and Ag₄–BPy complexes were much closer to the experimental results of BPy adsorbed on silver surface than that of Ag₃–BPy complexes. The vibrational frequencies that are sensitive to the planar or non-planar structure of BPy and to the dihedral angle of two pyridyl rings were discussed. The DFT results showed that the angles between two pyridyl rings for Ag–BPy and Ag₄–BPy were skewed by about 38.44° and 37.1°, respectively. The energy gaps of the HOMO and LUMO from DFT were 415–912 nm for BPy–Ag complexes. The relative intensities of SERS bands changed with different excitation laser lines. Thus, a chemical enhancement mechanism should play an important role in the SERS of BPy on silver substrate.     

尿嘧啶在银电极表面吸附状态的研究

综合分析了尿嘧啶在银电极表面不同条件的表面增强激光Ｒａｍａｎ光谱（ＳＥＲＳ）,利用扩展的Ｈüｃｋｅｌ分子轨道法（ＥＨＭＯ）对尿嘧啶分子在银电极表面的吸附状态进行了计算．结果表明：最稳定的吸附构型能较成功地阐明尿嘧啶吸附在银表面的ＳＥＲＳ谱;尿嘧啶在银表面主要是以Ｎ（３）去质子化的形式吸附;尿嘧啶在银表面的吸附取向是由其浓度和银表面电位共同决定;在较低浓度和较高电位时,Ｎ（３）去质子化的尿嘧啶离子在银表面主要是通过Ｃ（２）及整个嘧啶环上的π电子体系与银表面的相互作用平躺地吸附;在较高浓度和较低电位时,吸附取向发生改变,即主要是通过Ｎ（３）与Ｏ（１０）以及Ｎ（３）与Ｏ（８）垂直地共同吸附在银表面上     

Raman spectroscopy of gold nanoparticle conjugates of cosmetic ingredient kinetin

We performed a feasibility test of the cosmetic ingredient kinetin (KT)-gold nanoparticle (AuNP) conjugates by means of vibrational Raman spectroscopy and quantum mechanical calculations. The adsorptions of KT on AuNP surfaces were examined by absorption spectra and surface-enhanced Raman scattering (SERS). The size of KT at the initial concentrations of 10⁻⁵ M with the AuNP composites was measured to be 22 nm. Density functional theory (DFT) calculations were performed to estimate the energetic stabilities of KT on an Au cluster atom. The two tautomeric forms of 9H-amino and 7H-amino in KT are predicted to have similar energies on Au. The N3-coordinating geometries in both 9H-amino and 7H-amino forms of KT are predicted to be most stable on an Au cluster. Vibrational analysis also suggested that the two tautomers of KT should coexist in the adsorbed state on Au. The concentration-dependent SERS spectra of KT indicated that 5 × 10⁻⁵ M exhibited the highest SERS signals.     

苯胺在银和金电极上的表面增强拉曼光谱

聚苯胺作为性能较好的导电高聚物有很大的应用潜力,有关其聚合和导电机理的研究受到广泛重视。表面增强拉曼光谱(SERS)能现场(in situ)检测表面吸附分子、提     

Raman spectral study of metal-cytosine complexes: a density functional theoretical (DFT) approach

The fluctuation of surface-enhanced Raman scattering (SERS) spectra has been an obstacle to the analysis of the adsorbate on the metal surface. In this paper, we aim at using the density functional theory (DFT) to study the fluctuant Raman spectra of the cytosine molecule which interacts with a coinage metal atom or cation via N1 and N3 sites. The results show that the adsorption site strongly influences the Raman spectral property of cytosine molecule, especially the relative intensity of some bands. In addition, the SERS spectra of cytosine which is adsorbed on the gold, silver, and copper electrodes are measured, and the possible orientation and adsorption site of the cytosine molecule adsorbed on metal electrodes surface are proposed with the help of DFT simulations.     

Surface-enhanced Raman scattering of 4,4′-bipyridine on gold nanoparticle surfaces

The adsorption structure and mechanism of 4,4′-bipyridine (BiPy) on gold nanoparticle surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). The aromatic ring of BiPy appeared to assume a perpendicular orientation with respect to the gold surface from the presence of the ν(CH) band at ∼3060 cm⁻¹. The SERS intensities of several vibrational modes of BiPy on Au were found to vary as the bulk concentration. The SERS intensities for BiPy on Au could be ascribed to both the electromagnetic (EM) and charge transfer (CT) enhancement mechanism.     

金银纳米粒子的复合组装及表面增强拉曼光谱研究

采用自组装技术在硅基底上进行金银纳米粒子的混合组装, 通过控制组装溶液中金银溶胶的体积比而控制基底上金银纳米粒子的密度. SEM结果显示金银呈亚单层均匀分布, 以吡啶为探针分子, 在不同波长的激发光下研究了纯金、银以及混合组装时的SERS效应. 利用金银在不同激发线下增强效应的不同以及探针分子吸附在金银纳米粒子表面主要谱峰相对强度差别的特点, 通过一系列校正以及差谱方法研究了金银共存时SERS效应的变化, 并分离出混合体系中金的增强行为, 结果表明在金银同时组装时吡啶的SERS谱峰特征主要表现为银纳米粒子的行为, 分离出的金SERS光谱特征接近银的行为, 说明金银纳米粒子之间产生了一定的耦合作用.     

The pH dependent Raman spectroscopic study of caffeine

First of all the surface enhanced Raman spectroscopy (SERS) and normal Raman spectra of caffeine aqueous solution were obtained at different pH values. In order to obtain the detailed vibrational assignments of the Raman spectroscopy, the geometry of caffeine molecule was optimized by density functional theory (DFT) calculation. By comparing the SERS of caffeine with its normal spectra at different pH values; it is concluded that pH value can dramatically affect the SERS of caffeine, but barely affect the normal Raman spectrum of caffeine aqueous solution. It can essentially affect the reorientation of caffeine molecule to the Ag colloid surface, but cannot impact the vibration of functional groups and chemical bonds in caffeine molecule.     

Surface-enhanced Raman scattering investigation of the adsorption of 2-mercaptobenzoxazole on smooth copper surfaces doped with silver colloidal nanoparticles

The adsorption of 2-mercaptobenzoxazole on copper has been investigated by means of surface-enhanced Raman scattering (SERS) by doping smooth copper surfaces with silver colloidal nanoparticles. The metal surfaces have been characterized by means of atomic force microscopy measurements. The compound adsorbs on the Cu/Ag surfaces in its ionized thiolic form, adopting a tilted orientation with respect to the metal surface. The anion is chemisorbed through the sulfur and nitrogen atoms on the smooth copper surface, and the silver colloidal nanoparticles only enhance the Raman signal due to the electromagnetic mechanism. SERS data have been interpreted with the help of DFT calculations on models of the ligand bound to copper adclusters.     

Surface-enhanced Raman scattering of EDOT and PEDOT on silver and gold nanoparticles

Surface-enhanced Raman scattering (SERS) spectra of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and its monomer 3,4-ethylenedioxythiophene (EDOT) on Ag and Au nanoparticles presenting different morphologies and stabilizing agents have been obtained using the excitation radiation at 633 nm. The SERS spectra of the monomer and polymer are strongly dependent both on the metal and capping agent of the substrate. SERS spectra of EDOT on Au nanospheres indicates that adsorption occurs with the thiophene ring perpendicular to the metal surface. In contrast, polymerization takes place on the silver surface of Ag nanospheres. EDOT adsorption on Ag nanoprisms with polyvinylpyrrolidone (PVP) as capping agent occurs similarly to that observed on gold. Surface-enhanced resonance Raman scattering (SERRS) spectra of PEDOT on gold nanostars that present a thick layer of PVP show no chemical interaction of PEDOT with the metal surface; however, when PEDOT is adsorbed on citrate stabilized gold nanospheres, the SERRS spectra suggest that thiophene rings are perpendicular to the surface. Oxidation of PEDOT also is observed on Ag nanospheres. The investigation of the interface between PEDOT and metal surface is crucial for the development in polymer-based optoelectronic devices since this interface plays a crucial role in their stability and performance.     

TiO2电极表面氰基吡啶吸附的电化学SERS光谱

采用基于核壳纳米粒子的壳层隔绝纳米粒子增强拉曼(SHINERS)以及Au纳米粒子增强技术, 对比研究了4-氰基吡啶(4-CNPy)在TiO2表面的吸附行为. 结果表明, 采用2种技术所获得的光谱存在明显的差别. 利用前者得到了4-CNPy在TiO2电极上随电极电位变化的吸附方式. 在电位为0时, 分子以吡啶环上的N垂直吸附; 随电位负移, 部分分子变为倾斜吸附, 且在电位为-1.0 V时倾斜角度变大. 在正电位区间, 分子始终以吡啶环上的N垂直吸附. 而采用Au纳米粒子滴加在TiO2电极上的方式, 则得到吸附在TiO2, Au及TiO2/Au复合结构上的总光谱信息.     

Adsorption change of cyclohexyl acetylene on gold nanoparticle surfaces

The conformational changes of cyclohexyl acetylene (CHAL) on gold nanoparticle surfaces were investigated by means of concentration- and temperature-dependent surface-enhanced Raman scattering (SERS). Depending on concentrations and temperatures, the spectral changes of the acetylene ν(C≡C) stretching vibration on gold nanoparticles appeared to be more conspicuous than those of cyclohexyl ring modes. The density functional theory (DFT) calculation was performed at the level of B3LYP/6-31G++(d,p) to compare the energetic stability and vibrational frequencies of the various conformers of cyclohexanethiol (CHT) and CHAL. The DFT calculations were also carried out at the level of B3LYP/LACVP** on the CHAL molecule adsorbed on Au clusters at several sites to explain the spectral changes of the acetylene ν(C≡C) stretching vibration.     

Density functional theory (DFT) and DRIFTS investigations of the formation and adsorption of enolic species on the Ag/Al2O3 surface

Molecular structure and vibrational frequencies of the novel surface enolic species intermediate on Ag/Al2O3 have been investigated by means of density functional theory (DFT) calculations and in situ infrared spectroscopy. The geometrical structures and vibrational frequencies were obtained at the B3P86 levels of DFT and compared with the corresponding experimental values. Theoretical calculations show that the calculated IR spectra are in good agreement with the experimental spectroscopic results. In addition, the adsorption energy of enolic species on the Ag/Al2O3 catalyst surface was also evaluated. The reaction mechanism from C2H5OH to enolic species on Ag/Al2O3 catalyst was proposed.     

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(H2TMPyP)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H2TMPyP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H2TMPyP.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.