Structure of water at ionic liquid/Ag interface probed by surface enhanced Raman spectroscopy

The potential-dependent adsorption behavior of water and ionic liquid was probed by surface-enhanced Raman spectroscopy (SERS) at the Ag electrode surface in the ionic liquids containing water with different concentrations.The configuration of water at the ionic liquid/electrode interface and the relationship between the potential of zero charge (pzc) and the molar fraction of water were deduced through the changes in the vibrational frequency of OH stretching mode.A small Stark effect value was determined ...     

含水离子液体/金属界面结构的SERS研究

利用表面增强拉曼光谱(SERS)研究了不同含水量下离子液体及水分子在银电极上随电位变化吸附方式的改变,通过水的O-H伸缩振动谱峰频率变化特征,详细探究了水在离子液体/电极界面上的存在形式及作用方式以及体系零电荷电位与水含量的关系.水含量较低时O-H伸缩振动的Stark系数值较低,随水含量的增加O-H伸缩振动的谱峰位置逐渐向高波数方向移动,同时O-H伸缩振动的Stark系数也逐渐增大,1molL-1[BMIM]Br水溶液中达到76cm-1V-1,且体系的零电荷电位正移,这些差异与水在离子液体中所形成氢键的程度及水分子的存在形式密切相关,在水的含量较低时水与离子液体阳离子通过氢键作用而存在于界面层中,当水的含量增加时,水分子间氢键的作用增强,水与电极表面直接作用的可能性增大.     

Single-molecule surface enhanced resonance Raman spectroscopy of the enhanced green fluorescent protein

In the present contribution, we demonstrated that surface-enhanced resonance Raman scattering spectra from single green fluorescent proteins (GFPs) were obtained. The most important findings are the direct detection of the conversion between a deprotonated and a protonated form of the chromophore at the single-molecule level via the corresponding vibrational fingerprints, and the fact that the enhanced green fluorescent protein (EGFP) also shows a high surface enhanced resonance Raman scattering (SERRS) signal. Our findings show the potential of the technique to study structural dynamics of protein molecules at a single-molecule level.     

Ultrafast dynamics of myoglobin probed by time-resolved resonance Raman spectroscopy

Recent experimental work carried out in this laboratory on the ultrafast dynamics of myoglobin (Mb) is summarized with a stress on structural and vibrational energy relaxation. Studies on the structural relaxation of Mb following CO photolysis revealed that the structural change of heme itself, caused by CO photodissociation, is completed within the instrumental response time of the time-resolved resonance Raman apparatus used (approximately 2 ps). In contrast, changes in the intensity and frequency of the iron-histidine (Fe-His) stretching mode upon dissociation of the trans ligand were found to occur in the picosecond regime. The Fe-His band is absent for the CO-bound form, and its appearance upon photodissociation was not instantaneous, in contrast with that observed in the vibrational modes of heme, suggesting appreciable time evolution of the Fe displacement from the heme plane. The band position of the Fe-His stretching mode changed with a time constant of about 100 ps, indicating that tertiary structural changes of the protein occurred in a 100-ps range. Temporal changes of the anti-Stokes Raman intensity of the v4 and v7 bands demonstrated immediate generation of vibrationally excited heme upon the photodissociation and decay of the excited populations, whose time constants were 1.1 +/- 0.6 and 1.9 +/- 0.6 ps, respectively. In addition, the development of the time-resolved resonance Raman apparatus and prospects in this research field are described.     

Interaction of proflavine with DNA studied by colloid surface enhanced resonance Raman spectroscopy

The interaction of the mutagenic highly fluourescing proflavine (3,6-diaminoacridine: PF) dye with calf thymus DNA has been studied by Surface Enhanced Resonance Raman Scattering (SERRS). Since the Ag-colloids almost completely quenche the strong fluorescence it is possible to obtain excellent vibrational spectra in a wide frequency range providing valuable information about the intercalation. The intercalation does not affect the vibrational frequencies of the proflavine dye. On the other hand, intensity changes are observed in some of the ring- and NH₂-modes of proflavine upon intercalation. This Raman hypochromism is characteristic for ring stacking interactions and in the SERRS spetroscopy for an additional effects of the dye orientation to the surface.     

Non aggregated colloidal silver nanoparticles for surface enhanced resonance Raman spectroscopy

Silver nanoparticles with a tuneable λ max were produced as colloids by heterogeneous nucleation. The synthesis process is both fast and repeatable, producing stable PVA capped nanoparticles. The colloid's effectiveness in the SERRS system was investigated using Rhodamine 6G, R6G, Crystal Violet, CV, and Malachite Green, MG, as probe molecules. A clear sensing trend was observed, where the Raman signal emitted was significantly enhanced by the addition of silver nanoparticles. A build up of signal intensity is observed until an optimum ratio is achieved, followed by a decline in signal intensity as the concentration of nanoparticles is further increased. The sensing trend appeared to be dependant on the structure of these model molecules with similarly structured compounds exhibiting similar trends. Thus a maximum enhancement with the Ag: analyte molar ratio of ～ 5.56: 1, was seen for CV and MG whereas R6G had a maximum enhancement at the Ag: analyte molar ratio of ～ 2.25: 1.     

Gold particle interaction in regular arrays probed by surface enhanced Raman scattering

Lithographically designed two-dimensional arrays consisting of gold nanoparticles deposited on a smooth gold film are used as substrate to examine the SERS effect of the trans-1,2-bis (4-pyridyl) ethylene molecule. These arrays display two plasmon bands instead of the single one observed for the same arrays of particles but deposited on indium tin oxide coated glass. Laser excitation within the short wavelength band does not bring about any SERS spectrum, while excitation within the long wavelength band yields SERS spectra with a gain per molecule rising up to 10(8). The simultaneous investigation of extinction and Raman spectra of arrays exhibiting various topography parameters enables us to suggest an interpretation for both the occurrence of the two plasmon resonances and for the high Raman enhancement. We suggest to assign the short wavelength band to a plasmon wave propagating at the gold glass interface and the long wavelength one to an air/gold surface plasmon mode modified by particle-particle interaction.     

Stereochemical aspects of axial ligation in ferrous iron-porphyrins probed by resonance Raman spectroscopy

We report the concentration-dependent resonance Raman (RR) studies of the FEN_Im stretching modes in the photo-reduced iron-octaethyl porphyrin (Fe^IIOEP) and iron-protoporphyrin-IX dimethylester (Fe^IIPPDME) complexes with 2-methyl imidazole (2-MeIm) and 1,2-dimethyl imidazole (1,2-Me₂Im) as axial ligands. The FeN_Im stretching modes in both iron complexes have revealed two components due to the co-existence of the upright and tilted configurations of the FEN_Im bond with respect to the normal to the heme plane. The frequencies of the two components in both the complexes shift to higher side with an increase in concentration of 2-MeIm as axial ligand. With the more sterically hindered 1,2-Me₂Im as axial ligand, the (1,2-Me₂Im)Fe^II-OEP complex exists mainly with the tilted configuration of the FEN_Im bond while the upright configuration is the dominant species in the (1,2-Me₂Im)Fe^IIPPDME complex. From the comparative study, we infer that the vinyl groups in the protoporphyrin complex play a dominant role in non-bonded interactions with the sterically hindered axial ligands in stabilizing the specific configurations.     

Autoacetylation induced specific structural changes in histone acetyltransferase domain of p300: probed by surface enhanced Raman spectroscopy

Reversible acetylation of histone and non-histone proteins plays an important role in the regulation of gene expression and cellular homeostasis. A balance between acetylation and deacetylation of these proteins are maintained by histone acetyltransferases (HATs) and histone deacetylases (HDACs). Among different HATs, p300/CBP is the most widely studied chromatin modifying enzymes. p300 is involved in several physiological processes like cell growth, regulation of gene expression, development, and tumor suppressor, and therefore its dysfunction causes different diseases. The autoacetylation of p300 is one of the key regulators of its catalytic activity. Mechanistically, autoacetylation induced structural changes in the p300 HAT domain acts as a master switch. In this report, we have shown that the natural HAT inhibitor garcinol could potently inhibit the autoacetylation activity. Furthermore, for the first time, we demonstrate that indeed autoacetylation induces structural changes in p300 HAT domain, as probed by surface-enhanced Raman scattering. Presumably, SERS will be a very useful tool to find out the structural changes in the other self-modifying enzymes like kinases and methyltransferases.     

Semi-quantitative analysis of indigo by surface enhanced resonance Raman spectroscopy (SERRS) using silver colloids

In this paper we report for the first time semi-quantitative analysis of indigo using surface enhanced Raman spectroscopy (SERS) and surface enhance resonance Raman spectroscopy (SERRS). Indigo, a dye widely used today in the textile industry, has been used, historically, both as a dye and as a pigment; the latter in both paintings and in printed material. The molecule is uncharged and largely insoluble in most solvents. The application of SERS/SERRS to the semi-quantitative analysis of indigo has been examined using aggregated citrate-reduced silver colloids with appropriate modifications to experimental protocols to both obtain and maximise SERRS signal intensities. Good linear correlations are observed for the dependence of the intensities of the SERRS band at 1151 cm(-1) using laser exciting wavelengths of 514.5 nm (R=0.9985) and 632.8 nm (R=0.9963) on the indigo concentration over the range 10(-7)-10(-5) and 10(-8)-10(-5) mol dm(-3), respectively. Band intensities were normalised against an internal standard (silver sol band at 243 cm(-1)). Resonance Raman spectra (RRS) of aqueous solutions of indigo could not be collected because of its low solubility and the presence of strong fluorescence. It was, however, possible to obtain RS and RRS spectra of the solid at each laser excitation wavelength. The limits of detection (L.O.D.) of indigo by SERS and SERRS using 514.5 and 632.8 nm were 9 ppm at both exciting wavelengths. Signal enhancement by SERS and SERRS was highly pH dependent due to the formation of singly protonated and possibly doubly protonated forms of the molecule at acidic pH. The SERS and SERRS data provide evidence to suggest that an excess of monolayer coverage of the dye at the surface of silver colloids is observed at concentrations greater than 7.85x10(-6) mol dm(-3) for each exciting wavelength. The data reported herein also strongly suggest the presence of multiple species of the indigo molecule.     

Immunoassay for P38 MAPK using surface enhanced resonance Raman spectroscopy (SERRS)

A micro-bead sandwich assay for P38 mitogen-activated protein kinase using surface enhanced resonance Raman spectroscopy (SERRS) detection is reported. Monoclonal capture antibodies were immobilised on a solid phase of magnetic micro-beads with secondary detection using a rhodamine-labelled antibody. Quantitative SERRS detection of the secondary antibody was possible with a limit of detection of 9.5 x 10(-12) mol dm(-3). The sandwich assay was quantitative and sensitive to 6 ng ml(-1). The mechanism of the SERRS detection in the immunoassay was investigated. The addition of SERRS aggregating agents causes the dissociation of the immuno-complex from the magnetic beads. Scanning electron microscopy images indicate that the colloidal suspension rather than adsorbed silver nanoparticles on the beads provide the SERRS signals, that the aggregate size is partially controlled and that there is some inhomogeneity in the distribution of organic matter on the nanoscale.     

基于聚合物／金属纳米结构镶嵌型柔性基底的表面增强拉曼光谱技术

表面增强拉曼光谱（SERS）技术可极大增强传统拉曼光谱的信号强度,从而拓展拉曼光谱的应用范围．针对SERS技术在分析对象、分析环境的普适性和分析效率方面的限制,本文设计并发展了一种透明、柔性、自支撑SERS基底的制备、保存和使用方法．该基底由聚合物聚甲基丙烯酸甲酯（PMMA）和在其表面镶嵌的金属纳米结构组成,可以通过背入射法用于任意形貌样品表面的直接和在线检测．柔性SERS（Ag）基底在R6G水溶液表面的检测限小于1pmol／L．     

An optofluidic device for surface enhanced Raman spectroscopy

We have developed an optofluidic device that improves the sensitivity of surface enhanced Raman spectroscopy (SERS) when compared to other SERS approaches. This device has a pinched and step microchannel-nanochannel junction that can trap and assemble nanoparticles/target molecules into optically enhanced SERS active clusters by using capillary force. These SERS active clusters provide an electromagnetic enhancement factor of approximately 10(8). In addition, due to the continuous capillary flow that can transport nanoparticles/target molecules into the junction sites, the numbers of nanoparticles/target molecules and SERS active sites are increased. As a result, the detection limit of SERS for adenine molecules was better than 10 pM.     

DNA detection by dye labeled oligonucleotides using surface enhanced Raman spectroscopy

1. Download : Download high-res image (290KB)
2. Download : Download full-size image

     

Rapid monitoring of antibiotics using Raman and surface enhanced Raman spectroscopy

Comparatively few studies have explored the ability of Raman spectroscopy for the quantitative analysis of microbial secondary metabolites in fermentation broths. In this study we investigated the ability of Raman spectroscopy to differentiate between different penicillins and to quantify the level of penicillin in fermentation broths. However, the Raman signal is rather weak, therefore the Raman signal was enhanced using surface enhanced Raman spectroscopy (SERS) employing silver colloids. It was difficult by eye to differentiate between the five different penicillin molecules studied using Raman and SERS spectra, therefore the spectra were analysed by multivariate cluster analysis. Principal components analysis (PCA) clearly showed that SERS rather than the Raman spectra produced reproducible enough spectra to allow for the recovery of each of the different penicillins into their respective five groups. To highlight this further the first five principal components were used to construct a dendrogram using agglomerative clustering, and this again clearly showed that SERS can be used to identify which penicillin molecule was being analysed, despite their molecular similarities. With respect to the quantification of penicillin G it was shown that Raman spectroscopy could be used to quantify the amount of penicillin present in solution when relatively high levels of penicillin were analysed (>50 mM). By contrast, the SERS spectra showed reduced fluorescence, and improved signal to noise ratios from considerably lower concentrations of the antibiotic. This could prove to be advantageous in industry for monitoring low levels of penicillin in the early stages of antibiotic production. In addition, SERS may have advantages for quantifying low levels of high value, low yield, secondary metabolites in microbial processes.     

Intervalence involvement of bridging ligand vibrations in hexaruthenium mixed-valence clusters probed by resonance Raman spectroscopy

Resonance Raman spectroscopy, performed using spectroelectrochemistry and with excitation in the intervalence bands of three pyrazine-bridged, mixed-valence dimers of trinuclear ruthenium clusters, shows resonant enhancement of symmetric bridging ligand modes. The resonant enhancements and frequency shifts of these bridging ligand modes are observed as a function of varying electronic communication between charge sites, and they show that a three-state vibronic model which explicitly includes the participation of the bridging ligand is needed to explain the spectroscopic behavior of these near-delocalized complexes.     

DNA detection by surface enhanced resonance Raman scattering (SERRS)

This Education article outlines the different ways in which surface enhanced resonance Raman scattering (SERRS) can be used for the detection of DNA. The use of various different SERRS detection strategies that have allowed both sensitive and selective detection to be obtained is covered. Detection of DNA by SERRS involves the use of a dye with the DNA, whether as an intercalator or by direct covalent attachment. This generates strong SERRS signals that indicate the presence of the specific DNA sequence. The SERRS detection of DNA in different molecular biological assays is also discussed.     

Redox-linked protein dynamics of cytochrome c probed by time-resolved surface enhanced infrared absorption spectroscopy

Time-resolved surface enhanced infrared absorption (SEIRA) spectroscopy is employed to analyse the dynamics of the protein structural changes coupled to the electron transfer process of immobilised cytochrome c (Cyt-c). Upon electrostatic binding of Cyt-c to Au electrodes coated with self-assembled monolayers (SAMs) of carboxyl-terminated thiols, cyclic voltammetric measurements demonstrate a reversible redox process with a redox potential that is similar to that of Cyt-c in solution, and a non-exponential distance-dependence of the electron transfer rate as observed previously (D. H. Murgida and P. Hildebrandt, Chem. Soc. Rev. 2008, 37, 937). On the basis of characteristic redox-state-sensitive amide I bands, the protein structural changes triggered by the electron transfer are monitored by rapid scan and step scan SEIRA spectroscopy in combination with the potential jump technique. Whereas the temporal evolution of the conjugate bands at 1693 and 1673 cm(-1) displays the same rate constants as electron transfer, the time-dependent changes of the 1660-cm(-1) band are slower by about a factor of 2. The study demonstrates that time-resolved SEIRA spectroscopy provides further information about the dynamics and mechanism of interfacial processes of redox proteins, thereby complementing the results obtained from other surface-sensitive techniques. In comparison with previous surface enhanced resonance Raman spectroscopic findings, the present results are discussed in terms of the local electric field strengths at the Au/SAM/Cyt-c interface.     

On-chip ultra-thin layer chromatography and surface enhanced Raman spectroscopy

We demonstrate that silver nanorod (AgNR) array substrates can be used for on-chip separation and detection of chemical mixtures by combining ultra-thin layer chromatography (UTLC) and surface enhanced Raman spectroscopy (SERS). The UTLC-SERS plate consists of an AgNR array fabricated by oblique angle deposition. The capability of the AgNR substrates to separate the different compounds in a mixture was explored using a mixture of four dyes and a mixture of melamine and Rhodamine 6G at varied concentrations with different mobile phase solvents. After UTLC separation, spatially-resolved SERS spectra were collected along the mobile phase development direction and the intensities of specific SERS peaks from each component were used to generate chromatograms. The AgNR substrates demonstrate the potential for separating the test dyes with plate heights as low as 9.6 μm. The limits of detection are between 10(-5)-10(-6) M. Furthermore, we show that the coupling of UTLC with SERS improves the SERS detection specificity, as small amounts of target analytes can be separated from the interfering background components.     

Single molecule level detection of allophycocyanin by surface enhanced resonance Raman scattering

Single molecule level detection of the near-infrared fluorescent protein allophycocyanin (APC) has been achieved using surface enhanced resonance Raman scattering (SERRS). The detection limit using the peak height of the 440 cm(-1) band was 1 x 10(-13) mol l(-1), compared to 2 x 10(-12) mol l(-1) for the fluorescence peak at 660 nm.