Estimating resonance enhancement of Raman scattering by metal adatom-adsorbate complexes

Publications on surface-enhanced Raman scattering (SERS) in metal sols are perused. The discrepancy between extinction spectra for freshly formed sols and the SERS excitation spectra is found to be connected with different temperature modes used in different procedures for obtaining sols, the temperature difference leading to different concentrations of metal adatoms on sol particles. Once the presence of adatoms is accounted for, the nature of “hot” sol particles, which ensure the observation of values of the SERS enhancement coefficient G?10¹⁴?10¹⁵, can be explained and the reasons for the scarcity of such particles can be established. On compact hot sol particles, rigorous calculations of electromagnetic enhancement G _em in most cases yield G _em≤ 10¹⁴. That is why combining the coefficient σ_b of gigantic amplification of background, which is caused by electron RS in metal and which is connected with the existence of adatoms, with the coefficient σ_si of SERS enhancement in a metal-metal adatom-adsorbate adsorption complex gives σ_bσ_si ≥ 10⁸.     

静电纺纳米复合纤维柔性表面增强拉曼散射传感基底的研究进展

表面增强拉曼散射(Surface enhanced Raman scattering,SERS)是一种分子检测光谱技术,借助SERS基底,可对生物、化学等复杂体系中的痕量分子进行分析。 其中静电纺纳米纤维SERS基底由于具有高比表面积、可透气透水、柔韧可折叠弯曲等特点,在复杂体系中提取、过滤、浓缩痕量分子等应用场景中,其表面结构具有其他刚性SERS基底不可比拟的优势。然而,静电纺纳米纤维SERS基底的发展却受到制备方法的限制,存在检测灵敏度较低、制备过程复杂等问题。 因此,目前的研究工作主要集中在新型制备方法及工艺的开发。 本文综述了静电纺纳米金银复合纤维SERS基底的几种常用制备方法,包括直接混合纺丝法、化学吸附法、静电吸附法、物理沉积法和原位化学还原法,并总结了静电纺纳米纤维SERS基底在复杂体系中提取、过滤、浓缩待测分子的应用,最后对静电纺纳米复合纤维SERS基底的发展进行了展望。     

吡啶-氯化钾水溶液/n型硫化镉电极界面上的表面增强喇曼散射

本文研究了在吡啶-KC1水溶液中吡啶吸附在n-CdS电极上的表面增强喇曼散射(SERS)。在光照下,CdS电极经过正极化予处理数分钟,就能观察到吡啶吸附在CdS电极上的很强的SERS谱。其特征峰是1010和1036cm^-1与纯吡啶的喇曼特征峰991,1030cm^-1相比有了明显位移。又SERS谱随着吡啶浓度的增加而增强。外加电位对SERS也有一定影响,其曲线形状与CdS的I～V曲线很相似。对这些实验结果,本文用n型CdS电极的光电化学特性进行了初步的考察和讨论。     

等离子体金属纳米结构在SERS传感及可穿戴应力传感中的应用

等离子体金属(金、银)纳米结构因其特有的理化性能,被广泛应用于表面增强拉曼散射(Surface-enhanced Raman scattering,SERS)传感及可穿戴应力传感领域.其中,SERS是一种应用贵金属纳米材料增强拉曼散射信号的检测技术,该技术灵敏度高、特异性强,已被广泛用于生物医学、环境监测、食品药品检测...     

Surface-enhanced Raman scattering: realization of localized surface plasmon resonance using unique substrates and methods

Surface-enhanced Raman scattering (SERS) enhancement and the reproducibility of the SERS signal strongly reflect the quality and nature of the SERS substrates because of diverse localized surface plasmon resonance (LSPR) excitations excited at interstitials or sharp edges. LSPR excitations are the most important ingredients for achieving huge enhancements in the SERS process. In this report, we introduce several gold and silver nanoparticle-based SERS-active substrates developed solely by us and use these substrates to investigate the influence of LSPR excitations on SERS. SERS-active gold substrates were fabricated by immobilizing colloidal gold nanoparticles on glass slides without using any surfactants or electrolytes, whereas most of the SERS-active substrates that use colloidal gold/silver nanoparticles are not free of surfactant. Isolated aggregates, chain-like elongated aggregates and two-dimensional (2D) nanostructures were found to consist mostly of monolayers rather than agglomerations. With reference to correlated LSPR and SERS, combined experiments were carried out on a single platform at the same spatial position. The isolated aggregates mostly show a broadened and shifted SPR peak, whereas a weak blue-shifted peak is observed near 430 nm in addition to broadened peaks centered at 635 and 720 nm in the red spectral region in the chain-like elongated aggregates. In the case of 2D nanostructures, several SPR peaks are observed in diverse frequency regions. The characteristics of LSPR and SERS for the same gold nanoaggregates lead to a good correlation between SPR and SERS images. The elongated gold nanostructures show a higher enhancement of the Raman signal than the the isolated and 2D samples. In the case of SERS-active silver substrates for protein detection, a new approach has been adopted, in contrast to the conventional fabrication method. Colloidal silver nanoparticles are immobilized on the protein functionalized glass slides, and further SERS measurements are carried out based on LSPR excitations. A new strategy for the detection of biomolecules, particularly glutathione, under aqueous conditions is proposed. Finally, supramolecular J-aggregates of ionic dyes incorporated with silver colloidal aggregates are characterized by SERS measurements and correlated to finite-difference time-domain analysis with reference to LSPR excitations. Figure SPR and SERS images for isolated, elongated and two-dimensional gold nanostructures     

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.     

Silver–platinum core–shell nanoparticles for surface-enhanced Raman spectroscopy

Core–shell Ag@Pt nanoparticles have been synthesised by the means of seed-growth reaction including reduction of PtCl₄²⁻ with silver and replacing Ag atoms with Pt. Surface-enhanced Raman scattering (SERS) spectra of pyridine (which gives slightly different spectra when interacting with various metals) adsorbed on synthesised Ag@Pt clusters were measured. SERS measurements have revealed that deposition of the platinum layer causes near elimination of the spectral interferences from pyridine directly interacting with the silver core. The average SERS enhancement factor for pyridine adsorbed on the Ag@Pt clusters was estimated as equal to about 10³–10⁴, significantly higher than the SERS enhancement factor achievable on the pure platinum nanostructures. Using the silver core (instead of the previously used gold cores) allows for measurement of strong SERS spectra on the Pt covered nanostructures for the wider range of the excitation radiation. This procedure of platinum deposition was tested with various silver nanoparticles – produced with borohydride, citrate and citrate/borohydride methods – which substantially differ in size distribution. The application of formed Ag@Pt structures for obtaining intense Raman spectra for molecules adsorbed on only slightly modified platinum surfaces is discussed.     

Direct evidence of chemical effect of surface-enhanced Raman scattering observed on electrochemically prepared rough gold substrates

In this study, polypyrrole (PPy) films were electrochemically deposited on gold substrates roughened by an electrochemical triangular-wave oxidation-reduction cycles (ORC) in an aqueous solution containing 0.1N KCl. Then the substrates were heated from 25 to 50 °C and the corresponding SERS performances of PPy were observed in situ. The results indicate that the SERS enhancement capabilities of substrates are gradually raised from 25 °C to a maximum at 40 °C and monotonically decreased from 40 to 50 °C. These SERS enhancement capabilities ascribed to the charge transfers from PPy to Au, which are responsible for the chemical effects of SERS mechanisms, are successfully observed via SERS and high resolution X-ray photoelectron spectroscopy (HRXPS) analyses. The variation in content of the oxidized PPy peak of the double peaks in the range of 1000-1150 cm⁻¹ in SERS spectrum obtained on an Au substrate at different temperatures is consistent with its corresponding variation in the SERS intensity of PPy. The variation in content of the oxidized nitrogen of PPy deposited on an Au substrate at different temperatures revealed from an HRXPS analysis also confirms this consistence.     

Density functional theory and surface-enhanced Raman spectroscopy studies on endocrine-disrupting chemical,dimethyl phthalate

A method to monitor endocrine-disrupting chemical contamination phthalate esters (PAEs) by surface-enhanced Raman scattering (SERS) spectroscopy has been investigated. The molecular structure and assignment of the vibrations of dimethyl phthalate (DMP), forming short chains in PAEs, has been studied by density functional theory (DFT) calculations. The structure of DMP with the dihedral angles of 1C-6C-11C-13O and 4C-5C-18C-20O being 133.78° and −24.00°, respectively, has the lowest energy. Theoretical vibrational frequencies using B3LYP/6-31 + G(d) (after scaling) show excellent agreement with the experimental normal Raman spectrum. In the region 200–1800 cm⁻¹, SERS spectra of DMP were measured using ordered gold nanosubstrates. All except the weak signals in the normal Raman spectrum of DMP were successfully enhanced. These results demonstrate that SERS technology could be developed as a rapid method for screening of DMP.     

Electrodeposition of dendritic gold/silver nanaoparticles on disposable screen‐printed carbon electrode and its application of 4‐mercaptopyridine in in situ electrochemical surface‐enhanced Raman scattering

Column electrodes pretreated through oxidation–reduction cycles were traditionally used in electrochemical surface‐enhanced Raman scattering (SERS). In this study, a disposable screen‐printed carbon electrode was introduced into in situ electrochemical SERS through the electrodeposition of dendritic gold/silver nanoparticles (Au/AgNPs) onto the surface of the carbon working electrode to induce the SERS enhancement effect on the electrode. Scanning electron microscopy images showed that dendritic Au/AgNPs nanostructures could be fabricated under appropriate electrodeposition conditions and could present a minimum SERS factor of 4.25 × 10⁵. Furthermore, the absorbed behavior of 4‐mercaptopyridine was investigated under different potentials. The adsorption configuration was inferred to transform from ‘vertical’ to ‘lying‐flat’. The proposed new electrode combined with a portable Raman spectrometer could be useful in the identifying products or intermediates during electrochemical synthesis or electrochemical catalysis in in situ electrochemical SERS. Copyright © 2016 John Wiley & Sons, Ltd.     

Adsorption of l-histidine on copper surface as evidenced by surface-enhanced Raman scattering spectroscopy

The adsorption of l-histidine on a copper electrode from H₂O- and D₂O-based solutions is studied by means of surface-enhanced Raman scattering (SERS) spectroscopy. Different adsorption states of histidine are observed depending upon pH, potential, and the presence of the SO²⁻₄ and Cl⁻ ions. In acidic solutions of pH 1.2 the imidazole ring of the adsorbed histidine remains protonated and is not involved in the chemical coordination with the surface. The SO²⁻₄ and Cl⁻ ions compete with histidine for the adsorption sites. In solutions of pH 3.1 three different adsorption states of histidine are observed depending on the potential. Histidine adsorbs with the protonated imidazole ring oriented mainly perpendicularly to the surface at potentials more positive than −0.2 V. Transformation of that adsorption state occurs at more negative potentials. As this takes place, histidine adsorbs through the α-NH₂ group and the neutral imidazole ring. The Cl⁻ ions cause the protonation and detachment of the α-NH₂ group from the surface and the formation of the ion pair NH⁺₃ … Cl⁻ can be observed. In the neutral solution of pH 7.0 histidine adsorbs through the deprotonated nitrogen atom of the imidazole ring and the α-COO⁻ group at E ≥ −0.2 V. However, this adsorption state is transformed into the adsorption state in which the α-NH₂ group and/or neutral imidazole ring participate in the anchoring of histidine to the surface, once the potential becomes more negative. In alkaline solutions of pH 11.9 histidine is adsorbed on the copper surface through the neutral imidazole ring.     

Adsorption of -histidine on copper surface as evidenced by surface-enhanced Raman scattering spectroscopy

The adsorption of -histidine on a copper electrode from H₂O- and D₂O-based solutions is studied by means of surface-enhanced Raman scattering (SERS) spectroscopy. Different adsorption states of histidine are observed depending upon pH, potential, and the presence of the SO²⁻₄ and Cl⁻ ions. In acidic solutions of pH 1.2 the imidazole ring of the adsorbed histidine remains protonated and is not involved in the chemical coordination with the surface. The SO²⁻₄ and Cl⁻ ions compete with histidine for the adsorption sites. In solutions of pH 3.1 three different adsorption states of histidine are observed depending on the potential. Histidine adsorbs with the protonated imidazole ring oriented mainly perpendicularly to the surface at potentials more positive than −0.2 V. Transformation of that adsorption state occurs at more negative potentials. As this takes place, histidine adsorbs through the α-NH₂ group and the neutral imidazole ring. The Cl⁻ ions cause the protonation and detachment of the α-NH₂ group from the surface and the formation of the ion pair NH⁺₃ … Cl⁻ can be observed. In the neutral solution of pH 7.0 histidine adsorbs through the deprotonated nitrogen atom of the imidazole ring and the α-COO⁻ group at E ≥ −0.2 V. However, this adsorption state is transformed into the adsorption state in which the α-NH₂ group and/or neutral imidazole ring participate in the anchoring of histidine to the surface, once the potential becomes more negative. In alkaline solutions of pH 11.9 histidine is adsorbed on the copper surface through the neutral imidazole ring.     

Doping and metallic‐support effect evidenced on SERS spectra of polyaniline thin films

Surface‐enhanced Raman scattering (SERS) is a process with origins, electromagnetic and chemical. The electromagnetic enhancement consists of the excitation of surface plasmons in the metallic support of the thin film. With only the electromagnetic enhancement mechanism, the surface spectra should not differ from volume Raman spectra. However, between SERS and volume Raman spectra, there are differences resulting from the chemical reactions taking place at the polymer/metal interface, intermediated by solvent molecules, that finally depend on the types of polymers and metallic supports. Polyaniline (PAN) is an excellent material to emphasize the chemical component of SERS. This is due to its particular structure with a repeating unit that contains two entities at different weights—a reduced state and an oxidized state–that, in turn, react differently with a metallic substrate. SERS spectra depend on the oxidizing properties of the metal surface, which involves an intermediate compound of the types Ag₂O and Au₂O₃ when N‐methyl‐2‐pyrrolidinone is used as the solvent. This article presents new results concerning the surface chemical effects that produce variations of the PAN SERS spectra. The SERS spectra of the PAN emeraldine base (PAN‐EB) layered on Au support are characterized by a semiquinoid structure that we believe is induced on the intermediate compound Au₂O₃. In the presence of H₂SO₄, the SERS spectra change gradually as the degree of acid protonation doping increases. The SERS spectra of the fully protonated PAN‐EB are identical to those obtained on PAN emeraldine salt (PAN‐ES) synthesized by cyclic voltammetry in an acid medium and are invariable with the type of metallic support. The SERS spectra show that the emeraldine salt can be partially or totally deprotonated with water or NH₄OH. The deprotonation is complete for the Ag support and partial for the Au support. The SERS spectra of the fully protonated PAN‐EB are characterized by a double band with maxima at about 1330 and 1370 cm⁻¹. Although the generation process of positive charge on the macromolecular chain of PAN‐EB doped in the presence of (C₄H₉)₄NBF₄ is similar to that due to protonic acid doping, involving cation addition (C₄H or H⁺ ions, respectively) in SERS spectra, the complex band situated at about 1330–1370 cm⁻¹ no longer appears. The doping of PAN‐EB with FeCl₃ produces two polymer forms: a salt type characterized by a protonated structure similar to that found for PAN‐ES and a base type similar to the leucoemeraldine form. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2599–2609, 2000     

Surface-enhanced Raman scattering study of polymer on metals. III. Chemisorbed polybenzimidazole and its corrosion-inhibiting properties at high temperature

Chemisorption of polybenzimidazole on silver and copper etched with nitric acid has been observed by surface-enhanced Raman scattering (SERS). The polymer is found to react chemically with silver, forming a complexed film on the surface. The SERS spectra show that polybenzimidazole film inhibits oxidation of the metal at high temperature, unlike chemisorbed benzimidazole, benzotriazole, and poly(4-vinyl pyridine). © 1992 John Wiley & Sons, Inc.     

金与银电极表面甘氨酸分子吸附作用的SERS光谱研究

本文利用表面增强拉曼光谱(SERS)技术研究了甘氨酸在金与银基底表面的吸附作用特征。研究表明甘氨酸分子以COO-的不对称形式吸附于金电极表面,且NH2也是其可能的吸附位点;而在银电极表面,则主要是通过COO-的对称形式而吸附。在此基础上,进一步研究了电极电位与溶液酸碱性对吸附于粗糙化银电极表面甘氨酸分子吸附作用的影响。研究结果表明,甘氨酸分子中去质子化羧基的吸附作用受电位影响较小,而电位对-NH3+吸附作用的影响程度较大。另一方面,溶液pH值对银电极表面的甘氨酸分子吸附行为的影响也较为显著。随着溶液酸性减小羧基倾向于相对于电极表面平行吸附。这是由于随着溶液碱性增大氨基质子化程度的减小,有利于氨基在银电极表面吸附。这将改变分子的吸附构型使其更接近于电极表面。这些变化主要出现在pH值大于10的条件下。     

SERS and FDTD simulation of gold nanoparticles grafted on germanium wafer via galvanic displacement

Uniform and dense Au nanoparticles grown on Ge (Au/Ge) were fabricated by a facile galvanic displacement method and employed as surface‐enhanced Raman scattering (SERS) substrates. The substrates exhibited excellent reproducibility in the detection of rhodamine 6G aqueous solution with a relative standard deviation of <20%. The substrate showed a high Raman enhancement factor of 3.44 × 10⁶. This superior SERS sensitivity was numerical confirmed by the three‐dimensional finite‐difference time‐domain method, which demonstrated a stronger electric field intensity (|E/E₀|²) distribution around the Au nanoparticles grown on Ge. This facile and low‐cost prepared Au/Ge substrate with high SERS sensitivity and reproducibility might have potential applications in monitoring in situ reaction in aqueous solution. Copyright © 2014 John Wiley & Sons, Ltd.     

Improved surface-enhanced Raman scattering on optimum electrochemically roughened silver substrates

In this work, the effects of preparation conditions used in roughening silver substrates by electrochemical triangular-wave oxidation-reduction cycles (ORC) on surface-enhanced Raman scattering (SERS) were first investigated. The optimum roughening conditions for obtaining strongest SERS of Rhodamine 6G (R6G) are as follows. Ag electrodes were cycled in deoxygenated aqueous solutions containing 0.1 M NaCl from −0.3 to +0.2 V versus Ag/AgCl at 25 mV s⁻¹ for five scans. The SERS of R6G adsorbed on this optimum procedure-prepared roughened Ag substrate exhibits a higher intensity by one order of magnitude, as compared with that of R6G adsorbed on a normally roughened Ag substrate.     

Biomimetic preparation of core‐shell structured surface‐enhanced Raman scattering substrate with antifouling ability,good stability,and reliable quantitative capability

The fouling and stability are two most critical limiting factors for practical applications of surface‐enhanced Raman scattering (SERS)‐based microfluidic electrophoresis device. Herein, we present a novel biomimetic nanoengineering strategy to achieve a SERS substrate featuring antifouling ability, good stability, and reliable quantitative capability. Typically, by employing tea polyphenol as the reducing agent, the substrate made of silver core‐gold shell nanostructures in situ grown on silicon wafer surface is fabricated. The core‐shell nanostructures are further embedded with internal standard molecules. Remarkably, the fabricated substrate preserves distinct SERS effects, adaptable reproducibility, and reliable quantitative ability even if the substrate is incubated with 15% H₂O₂, 13% HNO₃, or 10⁸ CFU/mL bacteria, or suffered from 12‐day continuous vibration at 250 rpm/min in PBS buffer. As a proof‐of‐concept application, the DNA‐functionalized substrate is capable of precise quantification of Hg²⁺ with a limit of detection down to ca. 1 pM even in sewage water.     

A gold@silica core–shell nanoparticle-based surface-enhanced Raman scattering biosensor for label-free glucose detection

The gold nanostar@silica core–shell nanoparticles conjugated with glucose oxidase (GOx) enzyme molecules have been developed as the surface-enhanced Raman scattering (SERS) biosensor for label-free detection of glucose. The surface-immobilized GOx enzyme catalyzes the oxidation of glucose, producing hydrogen peroxide. Under laser excitation, the produced H₂O₂ molecules near the Au nanostar@silica nanoparticles generate a strong SERS signal, which is used to measure the glucose concentration. The SERS signal of nanostar@silica∼GOx nanoparticle-based sensing assay shows the dynamic response to the glucose concentration range from 25 μM to 25 mM in the aqueous solution with the limit of detection of 16 μM. The sensing assay does not show any interference when glucose co-exists with both ascorbic acid and uric acid. The sensor can be applied to a saliva sample.     

In-situ surface-enhanced Raman scattering and FT-Raman spectroscopy of black prints

The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective.