High-wavenumber FT-Raman spectroscopy for in vivo and ex vivo measurements of breast cancer

The identification of normal and cancer breast tissue of rats was investigated using high-frequency (HF) FT-Raman spectroscopy with a near-infrared excitation source on in vivo and ex vivo measurements. Significant differences in the Raman intensities of prominent Raman bands of lipids and proteins structures (2,800?C3,100?cm^?1) as well as in the broad band of water (3,100?C3,550?cm^?1) were observed in mean normal and cancer tissue spectra. The multivariate statistical analysis methods of principal components analysis (PCA) and linear discriminant analysis (LDA) were performed on all high-frequency Raman spectra of normal and cancer tissues. LDA results with the leave-one-out cross-validation option yielded a discrimination accuracy of 77.2, 83.3, and 100% for in vivo transcutaneous, in vivo skin-removed, and ex vivo biopsy HF Raman spectra. Despite the lower discrimination value for the in vivo transcutaneous measurements, which could be explained by the breathing movement and skin influences, our results showed good accuracy in discriminating between normal and cancer breast tissue samples. To support this, the calculated integration areas from the receiver-operating characteristic (ROC) curve yielded 0.86, 0.94, and 1.0 for in vivo transcutaneous, in vivo skin-removed, and ex vivo biopsy measurements, respectively. The feasibility of using HF Raman spectroscopy as a clinical diagnostic tool for breast cancer detection and monitoring is due to no interfering contribution from the optical fiber in the HF Raman region, the shorter acquisition time due to a more intense signal in the HF Raman region, and the ability to distinguish between normal and cancerous tissues.     

Surface-enhanced Raman scattering of 4-aminobenzenethiol on silver nanoparticles substrate

Active surface-enhanced Raman scattering (SERS) silver nanoparticles substrate was prepared by multiple depositions of Ag nanoparticles on glass slides. The substrate is based on five depositions of Ag nanoparticles on 3-aminopropyl-trimetoxisilane (APTMS) modified glass slides, using APTMS sol–gel as linker molecules between silver layers. The SERS performance of the substrate was investigated using 4-aminobenzenethiol (4-ABT) as Raman probe molecule. The spectral analyses reveal a 4-ABT Raman signal enhancement of band intensities, which allow the detection of this compound in different solutions. The average SERS intensity decreases significantly in 4-ABT diluted solutions (from 10⁻⁴ to 10⁻⁶ mol L⁻¹), but the compound may still be detected with high signal/noise ratio. The obtained results demonstrate that the Ag nanoparticles sensor has a great potential as SERS substrate.     

Surface enhanced Raman scattering at Ag electrodes in non-aqueous pyridine solutions

The surface enhanced Raman scattering (SERS) of interfacial pyridine and Br⁻ species at Ag electrodes from neat pyridine solutions containing tetra-n-butylammonium bromide is presented. The potential dependence of the SERS peak frequencies, bandwidths, and relative intensities is reported and interpreted in terms of pyridine reorientation in the double layer. A band at 221 cm⁻¹ is observed at certain potentials and is assigned to the AgN stretch for Ag surface pyridine species.     

Spatially resolved surface enhanced Raman spectroscopy: Feasibility,intensity dependence on sampling area and attomole mass sensitivity

Spatially resolved surface enhanced Raman scattering (SR SERS) from μm sized sampling areas has been observed in the electrochemical environment for the first time. Analysis of the equation for SR SERS intensity reveals that the detected signal should be area independent. This is demonstrated experimentally for the aqueous pyridine/Ag model system using 200 kW cm⁻² peak laser irradiance. The mass detection limits for SR SERS are found to be on the order of 10⁵ molecules or 0.17 attomoles!     

Surface-enhanced raman scattering from poly(4-vinyl pyridine)

Surface-enhanced Raman scattering (SERS) has been observed for poly(4-vinyl pyridine) absorbed onto silver island films. Bands near 1219 and 1613 cm^?1, which are weak in normal Raman spectra of PVP, are strong in SERS spectra, and the band near 1020 cm^?1, which is the strongest band in the normal spectra, is relatively weak in SERS. The strongest bands in the SERS spectra all belong to the same symmetry species as α_ZZ, implying that the pyridine moieties are adsorbed through the nitrogen atoms with a vertical conformation. The ring breathing mode of the pyridine rings is observed near 1020 cm^?1, a frequency characteristic of pyridinium ions or coordinated pyridine, providing further evidence for adsorption through the nitrogen atoms. Silver catalyzed photooxidation, which can lead to the appearance of artifacts in SERS spectra, particularly of polymers, can be reduced by overcoating SERS samples with thin films of polymers such as poly(methyl methacrylate) that have low Raman scattering cross sections.     

Surface-enhanced Raman scattering of pyridine and benzene in non-aqueous electrochemical systems of alcoholic solvents

We have studied surface-enhanced Raman scattering from the following non-aqueous electrochemical systems: 0.05 M pyridine/0.1 M LiCl/methanol/Ag electrode, 0.05 M pyridine/0.1 M LiCl/ethanol/Ag electrode, and 0.05 M benzene/0.1 M LiCl/ethanol/Ag electrode. Each SERS band of pyridine is found to show two distinctive steps to reach the maximum peak intensity after the reduction potential is applied, which seems to be related to the formation of adatomic silver particle clusters. SERS spectra of benzene show three bands at 995, 986 and 993 cm⁻¹, the potential dependence of which was studied in detail to confirm chemisorption effects.     

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.     

F.t.i.r. and Raman spectra of triphenylphosphine,triphenylarsine, triphenylstibine,and dibenzylsulphide

The f.t.i.r. and Raman spectra of triphenylphosphine, triphenylarsine, triphenylstibine, and dibenzylsulphide in the solid state at ca 80 K have been recorded over the ranges 3500-40 cm⁻¹ (infra-red, 1 cm⁻¹ resolution) and 1650-30 cm⁻¹ (Raman, 2 cm⁻¹ resolution). The data, particularly those in the low wavenumber region, are more extensive, more complete, and of higher quality than those obtained in previous studies. Detailed band assignments are given.     

Raman Optical Activity of Glucose and Sorbose in Extended Wavenumber Range

Raman optical activity (ROA) is pursued as a promising method for structural analyses of sugars in aqueous solutions. In the present study, experimental Raman and ROA spectra of glucose and sorbose obtained in an extended range (50–4000 cm⁻¹) are interpreted using molecular dynamics and density functional theory, with the emphasis on CH stretching modes. A reasonable theoretical basis for spectral interpretation was obtained already at the harmonic level. Anharmonic corrections led to minor shifts of band positions (up to 25 cm⁻¹) below 2000 cm⁻¹, while the CH stretching bands shifted more, by ∼180 cm⁻¹, and better reproduced the experiment. However, the anharmonicities could be included on a relatively low approximation level only, and they did not always improve the harmonic band shapes. The dependence on the structure and conformation shows that the CH stretching ROA spectral pattern is a sensitive marker useful in saccharide structure studies.     

Surface-enhanced Raman scattering sensing of trace fenthion coupled with stable silver colloids and OH stretching band of water as an internal standard

The detection of trace fenthion using surface-enhanced Raman scattering (SERS) was proposed via the OH stretching band of water serving as an internal standard. The adsorption process of fenthion on the silver nanoparticle aggregates was characterized by UV-Visible absorption spectrometry and the optimal adsorption time was about 20 min. The OH stretching band of H₂O molecule presented around 3100–3500 cm^–1 in SERS spectrum was identified by density functional theory and it was not interfered with other characteristic peaks of fenthion. The linearity was obtained from the concentrations divided by the ratio of the benzene ring stretching area around 1073 cm^–1 and the internal standard of OH stretching area from 3100 to 3500 cm^–1, while the detection limit was calculated as 0.46 µM. The proposed SERS detection method was used in analyzing lake water sample with the recovery of 94–99%.     

Application of surface-enhanced Raman spectroscopy to mechanistic electrochemistry: Oxidation of iodide at gold electrodes

The electrooxidation of dilute (1 mM) iodide at the gold-aqueous interface has been examined by rotating disk voltammetry combined with surface-enhanced Raman spectroscopy (SERS) in order to identify the surface species formed and hence to shed light on the electrooxidation mechanism. Marked changes in the SER spectra occur upon shifting the electrode potential through the region where faradaic current flows, the characteristic 123 and 158 cm⁻¹ bands associated with adsorbed iodide being supplemented and eventually supplanted by bands at 110, 145 and 160–175 cm⁻¹, the latter two being especially intense. The new bands are assigned to higher polyiodides and molecular iodine. The latter species appears to be the major interfacial product associated with faradaic current flow. Iodide forms an irreversibly adsorbed and electroinactive layer at gold in the absence of solution iodide, as evidenced by the survival of the 123 and 158 cm⁻¹ SERS bands even at far positive potentials under these conditions. The results obtained for dilute iodide solutions are compared and contrasted with those obtained at higher iodide concentrations. For the latter conditions, the observed “surface” Raman spectra arise from resonance enhancement of the thick insoluble iodine films and solution triiodide formed in the convective diffusion layer rather than from SERS of species present in the double layer. Criteria for distinguishing between these two possibilities for systems involving such electrogenerated species are described.     

Enhanced Raman spectroscopy coupled to chemometrics for identification and quantification of acetylcholinesterase inhibitors

In this work, we present a new complete method using Surface Enhanced Raman Spectroscopy (SERS) and chemometrics for the qualitative and quantitative detection of pesticides by measuring the acetylcholinesterase (ACHE) activity. The Raman SERS is not only used for measuring the ACHE activity, but also for the direct detection of pesticides individually and for their identification. Gold nanoparticles (AuNPs) were used as dynamic SERS substrates for sensitive monitoring of ACHE activity in the presence of very low levels of organophosphate and carbamate pesticides, chemical warfare agents that are known to be ACHE inhibitors. The lowest detectable level for paraoxon was determined at 4.0 × 10⁻¹⁴ M and 1.9 × 10⁻⁹ M for carbaryl. The use of the enzyme allowed limits of detection for both pesticides that were much lower than the limits obtained by direct SERS analysis of the pesticides. The system shows a linear relationship between the intensity band at 639 cm⁻¹ and pesticide concentration. These results suggest that this biosensor could be used in the future for the non-selective detection of all ACHE inhibitors at very low concentrations with possible identification of the inhibitor.     

Development of a Fiber Optic Probe to Measure NIR Raman Spectra of Cervical Tissue In Vivo

The goal of this study was to develop a compact fiber optic probe to measure near infrared Raman spectra of human cervical tissue in vivo for the clinical diagnosis of cervical precancers. A Raman spectrometer and fiber optic probe were designed, constructed and tested. The probe was first tested using standards with known Raman spectra, and then the probe was used to acquire Raman spectra from normal and precancerous cervical tissue in vivo. Raman spectra of cervical tissue could be acquired in vivo in 90 s using incident powers comparable to the threshold limit values for laser exposure of the skin. Although some silica signal obscured tissue Raman bands below 900 cm^-1, Raman features from cervical tissue could clearly be discerned with an acceptable signal-to-noise ratio above 900 cm^-1. The success of the Raman probe described here indicates that near infrared Raman spectra can be measured in vivo from cervical tissues. Increasing the power of the excitation source could reduce the integration time to below 20 s.     

Vibrational spectroscopic study of syngenite formed during the treatment of liquid manure with sulphuric acid

Syngenite (K₂Ca(SO₄)₂·H₂O), formed during treatment of manure with sulphuric acid, was studied by infrared, near-infrared (NIR) and Raman spectroscopy. C_s site symmetry was determined for the two sulphate groups in syngenite (P2₁/m), so all bands are both infrared and Raman active. The split ν₁ (two Raman+two infrared bands) was observed at 981 and 1000 cm⁻¹. The split ν₂ (four Raman+four infrared bands) was observed in the Raman spectrum at 424, 441, 471 and 491 cm⁻¹. In the infrared spectrum, only one band was observed at 439 cm⁻¹. From the split ν₃ (six Raman+six infrared) bands three 298 K Raman bands were observed at 1117, 1138 and 1166 cm⁻¹. Cooling to 77 K resulted in four bands at 1119, 1136, 1144 and 1167 cm⁻¹. In the infrared spectrum, five bands were observed at 1110, 1125, 1136, 1148 and 1193 cm⁻¹. From the split ν₄ (six infrared+six Raman bands) four bands were observed in the infrared spectrum at 604, 617, 644 and 657 cm⁻¹. The 298 K Raman spectrum showed one band at 641 cm⁻¹, while at 77 K four bands were observed at 607, 621, 634 and 643 cm⁻¹. Crystal water is observed in the infrared spectrum by the OH-liberation mode at 754 cm⁻¹, OH-bending mode at 1631 cm⁻¹, OH-stretching modes at 3248 (symmetric) and 3377 cm⁻¹ (antisymmetric) and a combination band at 3510 cm⁻¹ of the H-bonded OH-mode plus the OH-stretching mode. The near-infrared spectrum gave information about the crystal water resulting in overtone and combination bands of OH-liberation, OH-bending and OH-stretching modes.     

On the occurrence of the central line (1025 cm) in the SERS spectra of pyridine adsorbed on silver hydrosols

The occurrence of a central line at 1025 cm⁻¹ between the surface-enhanced Raman scattering (SERS) bands of pyridine at 1008 and 1036 cm⁻¹ has been first detected in silver hydrosols. This band, which has no counterpart in the Raman spectrum of the free ligand, is observed in acidic aqueous suspension as corresponding to that observed in an electrochemical cell and attributed to adsorption of pyridinium cation. When pyridine is adsorbed on an aged colloid in an alkaline medium two different species are detected. A central band at about the same wave number occurs, attributable to pyridine bound to silver ion cluster on the metal surface, oxidised by ambient air.     

Structure of 4‐biphenylthiolate on Au nanoparticle surfaces studied by UV‐Vis absorption spectroscopy,transmission electron microscopy and surface‐enhanced Raman scattering

Structure of 4‐biphenylthiolate on Au nanoparticle surfaces has been studied by UV‐Vis absorption spectroscopy, transmission electron microscopy and surface‐enhanced Raman scattering (SERS). 4‐Biphenylthiolate is found to have a standing geometry on Au from the presence of the benzene ring CH stretching band identified at ～3060 cm^?1. The ν_8a band at 1597 cm^?1 in the ordinary Raman spectrum was found to split clearly into two features at 1599 and 1585 cm^?1. This result suggests that orientation of the phenyl rings in 4‐biphenylthiolate may be quite different and should not lie in the same plane on Au nanoparticle surfaces. On the basis of the electromagnetic enhancement factor, the dihedral angle could be estimated with a reported value of the tilt angle. Copyright © 2004 John Wiley & Sons, Ltd.     

Different level of fluorescence in Raman spectra of montmorillonites

The paper presents the study of selected montmorillonite standards by Raman spectroscopy and microscopy supported by elemental analysis, X-ray powder diffraction analysis and thermal analysis. Dispersive Raman spectroscopy with excitation lasers of 532 nm and 780 nm, dispersive Raman microscopy with excitation laser of 532 nm and 100× magnifying lens, and Fourier Transform-Raman spectroscopy with excitation laser of 1064 nm were used for the analysis of four montmorillonites (Kunipia-F, SWy-2, STx-1b and SAz-2). These mineral standards differed mainly in the type of interlayer cation and substitution of octahedral aluminium by magnesium or iron. A comparison of measured Raman spectra of montmorillonite with regard to their level of fluorescence and the presence of characteristic spectral bands was carried out. Almost all measured spectra of montmorillonites were significantly affected by fluorescence and only one sample was influenced by fluorescence slightly or not at all. In the spectra of tested montmorillonites, several characteristic Raman bands were found. The most intensive band at 96 cm⁻¹ belongs to deformation vibrations of interlayer cations. The band at 200 cm⁻¹ corresponds to deformation vibrations of the AlO₆ octahedron and at 710 cm⁻¹ can be assigned to deformation vibrations of the SiO₄ tetrahedron. The band at 3620 cm⁻¹ corresponds to the stretching vibration of structural OH groups in montmorillonites.     

Raman spectrum and secondary structure of the phage λ operator site OL1: evidence for multiple nucleoside conformations in an aqueous B-form DNA

The laser Raman spectrum of O_L1 has been obtained in the region 600–850 cm⁻¹ and the data have been interpreted in terms of different nucleoside conformations within the 17 base pair operator site. The O_L1 sequence, which is one of the tightest binding sites for the cI and Cro repressors of bacteriophage λ, displays several Raman conformation markers indicative of more than one backbone geometry for the same double-stranded DNA helix. Specific assignments for the Raman conformation markers are suggested by analogy with spectra of DNA single crystals and DNA fibers of known structure. Two Raman bands diagnostic of B-DNA backbone geometry are observed at 825 ± 3 and 838 ± 3 cm⁻¹, and may be due, respectively, to inequivalent conformations of GC and AT pairs. In addition, a weak band at 706 cm⁻¹ and a shoulder near 807 cm⁻¹ are consistent with a minor contribution from residues which assume the A-DNA backbone geometry or a structurally related configuration. The complex bandshape in the 650–700 cm⁻¹ interval, which is resolved into four peaks by Fourier deconvolution, is also consistent with the presence of multiple nucleoside conformers in O_L1 in physiological conditions.     

Vibrational spectra of halogen substituted cyclopropanes—V. Trans-1,2-dichlorocyclopropane

The i.r. spectra of gaseous trans-1,2-dichlorocyclopropane were measured from 4000 to 400 cm⁻¹ and to 200 cm⁻¹ in the liquid phase. The Raman spectrum of the liquid was obtained from 4000 to 50 cm⁻¹. An assignment of all 21 normal vibrations was proposed on the basis of i.r. vapour phase band contours, Raman depolarization ratios, expected group frequencies and comparison with closely related molecules. There is excellent agreement with the normal modes previously assigned for the cis and trans isomers of the chloro, bromo and iodo analogues. The data indicate little interaction between the two CHCl moieties.     

Vibrational spectra of isomeric pyridinic carboxylic acids in solid state and in solution and their SERS studies in silver sol

Raman spectroscopic studies of three isomeric pyridinic carboxylic acids, viz. picolinic, nicotinic and iso-nicotinic acid in solid state, in aqueous solution and in silver hydrosol, in the frequency range 900–1750 cm⁻¹, have been made. Assignments of the observed bands have been proposed in relation to the molecular forms present in solid state and in solution. Different degrees of intensity enhancements of the Raman bands in surface-enhanced Raman scattering (SERS) have been observed in all the three isomeric molecules. In iso-nicotinic acid, the intensity enhancement has been found to be minimum. Comparisons of Raman spectra in aqueous solution with those due to SERS in silver sol indicate that picolinic and nicotinic acid adsorb perpendicularly to the sol surface whereas in iso-nicotinic acid it occurs via donation of a π-electron of the aromatic ring, i.e. the plane of the ring lies parallel to the surface of the sol.