Raman Microscope System Research Articles

SERRS. In situ substrate formation and improved detection using microfluidics.

Surface-enhanced resonance Raman scattering (SERRS) of a model derivative of TNT was detected using a microflow cell designed within the framework of the lab-on-a-chip concept, using only the analyte and readily available reagents. The SERRS substrate, silver colloid, was prepared in situ, on-chip, by borohydride reduction of silver nitrate. The silver colloid was imaged within the chip using a white light microscope in either transmission or, due to the high reflectivity of the colloid, reflection mode. A fine stream of colloid approximately 30 microm in width was formed in a 250-microm-wide channel at the point where the colloid preparation reagents met. The chip was designed to produce a concentrated stream of colloid within a laminar regime, such that particles did not readily disperse into the fluid. One result of this was to reduce the effective volume of analysis. Attempts to deliberately disrupt this stream with microstructured pillars, fabricated in the fluidic channels, were unsuccessful. The chip was also designed to have the appropriate dimensions for detection using a modern Raman microscope system, which collects scattering from a very small volume. A dye derived from TNT was used as a model analyte. Quantitative behavior was obtained over 4 orders of magnitude with a detection limit of 10 fmol. This performance is between 1 and 2 orders of magnitude better than that achieved using a macroflow SERRS cell. The technique has the added advantage that both reagent consumption and effluent production are greatly reduced, leading to reduced operating costs and a decreased environmental impact

Lattice dynamics and elastic properties of zinc-blende MgS

Magnesium sulphide (MgS) normally crystallizes in the rocksalt structure; using a recent development in molecular beam epitaxy, it is now possible to obtain MgS in the zinc-blende structure grown on GaAs. A Raman microscope system with ultraviolet excitation at 244 nm has been used to obtain the Raman spectra of this material, revealing strong signals due to overtones of the LO and TO phonons in the backscattering geometry at room temperature. The strength of the signals implies that the excitation energy (5.08 eV) is close to resonance with the MgS band gap. Calculations of the frequency of the zone-center TO and LO phonons of this structure via ab initio methods are in excellent agreement with the experimental observations. The calculated and measured phonon frequencies were 433 and $425 {\mathrm{cm}}^{\ensuremath{-}1}$ (LO) and 335 and $327 {\mathrm{cm}}^{\ensuremath{-}1}$ (TO), respectively. Values for the lattice parameter and the elastic constants ${c}_{11}$ and ${c}_{12}$ of zinc-blende MgS were also obtained.

Raman Microprobe Spectroscopy of Halloysite

AbstractThe Raman spectra of a tubular halloysite originating from Matauri Bay, New Zealand, have been obtained using a Renishaw 1000 Raman microscope system. The Raman microprobe enables the Raman spectra of crystals as small as 0.8 μm diameter to be obtained over the complete wavelength range and allows spectral variations along the different crystal axes to be studied. Three bands in the hydroxyl stretching region were observed at 3616.5, 3623.4 and 3629.7 cm-1 and are attributed to the inner hydroxyls of the shared lower plane of the octahedral sheet of the halloysite. Two bands at 3698.2 and 3705 cm−1 were obtained for the outer hydroxyls of the unshared outer octahedral plane. The relative intensity of the 3629.7 cm−1 band varied according to the tube orientation. Lattice vibrations of the halloysite were also found to be orientation-dependent.

Comparison of X-ray patterns and Raman spectra of n= 2 and 3 Aurivillius phases by principal component analysis

Eight series of n= 2 and 3 Aurivillius phases with structures derived from the original Bi2An–1BnO3n+3 structure by fractional substitution in the (Bi2O2)2+ sheets as well as in the perovskite-type blocks (An–1BnO3n+1)2– have been prepared by solid-state reaction. Raman spectra of all 45 samples are shown and the origin of the vibrational modes discussed. Plots of the first two principal components of principal component analysis (PCA) of the X-ray data and Raman data for all the samples as well as within the n= 2 and 3 subsets are presented. The structural and compositional information contained in the Raman spectra and in the X-ray patterns is preserved in the PCA. Differences between the PCA results of the X-ray data and the Raman data are caused by the different sensitivities of the two techniques towards the various properties changed by the fractional substitutions. The availability of fast data acquisition and the quality of the PCA results suggest that a Raman microscope system in connection with a multivariate data analysis technique based on PCA can be a powerful tool for in situ quality control of devices based on these materials.

Coupling FT Raman and FT SERS microscopy with TLC plates for in situ identification of chemical compounds

Direct analysis of sub-femtogram quantities of chemical compounds on thin layer chromatography plates has been made possible by associating Fourier transform Raman microspectroscopy with SERS spectroscopy. The interfacing elements of the FT Raman microscope system are discussed and optimised such that a lateral resolution on the micron scale is achieved in the sample plane. Micro-FT SERS results obtained from a model biological molecule indicate preservation of molecular conformation upon adsorption at the SERS active surface. With NIR radiation it is thus possible to analyse plates with or without fluorescence indicators.

Remote Raman spectroscopic studies of corrosion products formed on nuclear fuel claddings used in PWR and AGR systems

AbstractThe construction of a remote Raman microscope system with a variable microscope‐to‐spectrometer distance of up to 3 m is described. Oxidative surface corrosion products on zirconium alloy and stainless‐steel nuclear fuel claddings for pressurized water and advanced gas cooled reactor systems produced under various conditions were studied and the potential of the technique for in situ analysis is discussed. Under the conditions studied experimentally, the major corrosion products are found to be α‐ZrO2 and α‐Fe2O3 for the zirconium alloy and stainless‐steel claddings, respectively.

In Situ Detection and Identification of Trace Explosives by Raman Microscopy

Abstract The innovative design of the newly developed Renishaw Raman Microscope system and its application to the in situ detection and identification of plastic explosives contained in fingerprint samples are presented. Raman microscopy is a nondestructive inspection method. Our experimental results show that Raman spectra and Raman band images can be obtained from explosive particles as small as 1 µm3 in size or 1 picogram in mass. After exploring the full potential of the Raman microscopic technique, the aim of this research is to develop a real-time and field-deployable plastic explosive detection system.

Patterns of stress-induced phase transformation in MgO-stabilized zirconia ceramic revealed using micro-Raman imaging

An automated Raman microscope system has been used to collect mapped Raman data from a Goodfellow 3% MgO stabilized zirconia ceramic tile. The data have been transformed to produce images which show the relative concentrations and distributions of the monoclinic and tetragonal phases in the mapped areas. The images reveal concentrations of the monoclinic phase at grain boundaries. Regions surrounding indents in the tile created with a Vickers hardness tester, were also mapped to reveal the extent and pattern of stress-induced phase transformation. A Raman map was also generated from an area before and after indentation. Comparison of the Raman images with the optical white light images reveals a relationship between the pattern of grain boundaries on the sample and the distribution of transformed material.

Raman spectra of the model B-DNA oligomer d(CGCGAATTCGCG)2 and of the DNA in living salmon sperm show that both have very similar B-type conformations

Raman spectra were obtained from aqueous solutions of the deoxyoligonucleotide d(CGCGAATTCGCG)2 (I), which has been suggested as a model for B-type DNA conformation. These spectra were compared with the Raman spectra of the aqueous solutions of several DNAs of natural origin taken under identical solution conditions. Since the model sequence has a high percent GC (66%), the Raman spectrum was compared with the Raman spectrum of the DNA from Micrococcus lysodeikticus (72% GC), and the spectra of the two different DNAs were found to be rather similar in both 50 mM salt and 6 M salt solutions. Computer-aided band-shape analysis of the backbone vibrational region of the Raman spectra shows the existence of several bands corresponding to different furanose ring puckers. This appears to indicate a heterogeneity of furanose ring pucker in both the model dodecamer and the native DNA. Significant differences were found in the intensity of the conformational marker band at 810 cm-1, which indicates corresponding differences in furanose ring pucker heterogeneities in these two high GC content DNAs. The Raman spectrum of the dodecamer (I) was used to analyze the Raman spectrum of the DNA inside the head of living intact salmon sperm. Sperm spectra were taken with both our conventional Raman spectrograph and a newly developed intracavity laser Raman microscope system. Although the DNA in the sperm head is required by packing considerations to be in a highly compact and condensed state, the Raman spectra of the intact sperm are almost identical with that of the model dodecamer (I) if the difference in base composition is taken into account.(ABSTRACT TRUNCATED AT 250 WORDS)