Fourier Transform Raman Spectrometer Research Articles

Effect of white tea extract incorporated calcium silicate cements on flexural strength and collagen degradation of dentin

ABSTRACT Aim: The aim of the study was to comparatively evaluate the effect of white tea extract-incorporated mineral trioxide aggregate (MTA) and Biodentine (BD) on collagen degradation and flexural strength of coronal dentin. Methods: Two hundred and fifty dentin beams (10 mm × 2 mm × 2 mm) were obtained from the mid-coronal portion of caries-free human 3rd molars. They were randomly assigned to five experimental groups (n = 50). Group 1-control group (No experimental materials placed); Group 2-MTA; Group 3-MTA with 10% white tea extract (WMTA); Group 4-BD; and Group 5-BD with 10% white tea extract (WBD). All experimental materials were mixed and then spread onto the prepared dentin beams. Each group was further divided into five subgroups with each 10 samples according to aging periods of 24 h, 1, 3, 6 months, and 1 year as A, B, C, D, and E, respectively. The dentin beams were placed in contact with a set calcium silicate cement block in silicone molds, with only one side of each beam exposed to the cement at 37°C in a 100% relative humidity chamber. At each designated time period, the beams were copiously rinsed with deionized water and tested for flexural strength and collagen degradation using a universal testing machine and Fourier Transform-Raman spectrometer, respectively. Flexural strength results were statistically analyzed using one-way ANOVA, followed by post hoc adjustment with Tukey’s test for pair-wise comparisons with P < 0.05. Results: Collagen degradation was more in Group 2, followed by 4, 3, and 5. All the groups showed a gradual reduction in flexural strength over 1 year. Group 2 showed the highest reduction in flexural strength over 1 year. Group 5 showed the least reduction in flexural strength. Conclusion: BD and white tea-incorporated BD showed less collagen degradation and better flexural strength than MTA and white tea-incorporated MTA, respectively.

Detection of aspirin traces in blood by means of surface‐enhanced Raman scattering spectroscopy

AbstractAspirin being freely available as an over the counter drug has a high overdose risk and can cause severe health symptoms. The methods used in clinics for the detection of such drugs (pharmaceuticals) in bodily fluids are mostly based on liquid chromatography and mass spectroscopy. These methods are known to be precise; however, they both require long and laborious sample preparation; thus, it takes time to acquire the required information. Because in the case of an overdose, the time has high importance, and faster methods would be beneficial. This work presents an application of a Surface‐enhanced Raman scattering (SERS) spectroscopic method for the detection of salicylic acid as a metabolite of aspirin in the blood serum of the patient under examination. In this research, the various colloidal solutions were employed for the preparation of SERS active substrates. The choice of the most efficient colloidal solution and the challenges of collecting SERS spectra of whole blood or its components are discussed. The spectra of both the model and the real‐life blood samples containing metabolite of aspirin were collected with a Fourier transform Raman spectrometer. The analysis of the collected spectra revealed that label‐free SERS can be used for the detection of salicylic acid with concentration down to 3 mM in blood serum corresponding to consumption of at least eight standard pills of aspirin (equivalent to mild toxicity). The proposed diagnostic method could be applied faster than the standard methods and could allow sensitive and fast diagnosis of aspirin consumption in the human blood.

One‐mirror, one‐grating spatial heterodyne spectrometer for remote‐sensing Raman spectroscopy

AbstractRecently, we evaluated a new type of Fourier transform Raman spectrometer, the spatial heterodyne Raman spectrometer (SHRS), which provides high‐resolution Raman spectra without the need for an entrance slit. An SHRS is a variant of a Michelson interferometer in which the mirrors in the arms of a Michelson interferometer are replaced by two stationary diffraction gratings. Instead of sampling path length differences temporally, as in the case of a Michelson interferometer, SHRS samples path length differences spatially at a two‐dimensional array detector. Applying a Fourier transform to the resulting interferogram recovers the desired spectrum. In the modified SHRS (mSHRS) instrument used in the present work, one of the diffraction gratings has been replaced by a stationary λ/10 mirror. This modification has a few effects. First, the detector records a greater number of photons, as spectral light is not lost into unused diffraction orders in the mirror arm of mSHRS. Second, the free spectral range (wavelength coverage) is doubled, whereas the spectral resolution is cut in half. In this work, the authors present remote‐sensing Raman spectra of minerals, organics, and biomarkers using this mSHRS for the first time.

Standoff spatial heterodyne Raman spectrometer for mineralogical analysis

Raman spectroscopy is ideally suited for planetary exploration because of its ability to unambiguously identify minerals, organic compounds, and biomarkers. Traditionally, Raman spectra were acquired with grating‐based dispersive spectrometers that require tens of micrometer‐sized entrance slits and thus limited light throughput. Recently, we have evaluated a new type of Fourier transform Raman spectrometer, the spatial heterodyne Raman spectrometer that provides high spectral resolution in a compact system without limiting light throughput. In this work, we present time‐resolved Raman spectra of carbonate, sulfate, and silicate minerals, including low Raman scattering efficiency olivine and feldspar minerals, in the 100–1260 cm−1 Raman fingerprint region with spatial heterodyne Raman spectrometer using 1.5‐cm‐diameter pulsed 532.078‐nm Nd:YAG laser beam. Copyright © 2017 John Wiley & Sons, Ltd.

The Research of Spatial Heterodyne Raman Spectroscopy with Standoff Detection

Spatial heterodyne Raman spectroscopy (SHRS) is a new type of Raman spectroscopic detection technique with characteristics of high optical throughout, high spectral resolution, and no moving parts. SHRS is very suitable for the planetary exploration missions, which can be used to the analysis of minerals and find the biomarkers maybe exist on the surface of planetary. The authors have applied the technique to the standoff Raman spectroscopic detection, analyzed the main characteristics, including spectral resolution, bandpass and signal to noise (SNR), of standoff SHRS and proved it through experiments. The basic theory of standoff SHRS has been described briefly while a breadboard has been designed, built and calibrated. On the basis, the Raman spectra of some inorganic solids, organic liquids and some natural minerals have been achieved at a distance of 10 m, the SNR of the breadboard has been estimated. Due to the poor adjustment and the defects of the optical elements, the breadboard is far away from an ideal system. But the results show that the SNR is better than 5 for most of the main Raman peaks of the samples, which can meet the basic requirement of clear positive detection of typical Raman peaks and the feasibility of standoff SHRS has been proved. SHRS can overcome the main defects of dispersive grating Raman spectrometers and Fourier transform Raman spectrometers and it has a great application prospect on the detection and analysis of the planetary surface. The work of the authors can prove the potentiality of SHRS on standoff detection and can provide reference for the engineering realization of standoff SHRS.

Effects of Catalyst on Carbon Nanotubes Synthesized by Thermal Chemical Vapor Deposition Method

The effects of cobalt, nickel and iron catalyst on carbon nanotubes (CNTs) were examined with scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractrometer (XRD) and Fourier transform Raman spectrometer (FT-Raman). The samples were prepared by the thermal chemical vapor deposition (CVD) method at 780 °C under pressure of acetylene gas (C2H2) at 0.5 bar. The average diameter of CNTs grown on Co, Fe and Ni catalyst obtained from SEM image is 100, 90, 70 nm, respectively. The crystallinity and the yield of CNTs synthesized from Ni catalyst were higher than that from Fe or Co catalyst. The Raman peak of radial breathing mode (RBM) region and the TEM images highlighted the hollow tubes of the CNTs. The results indicated that the diameter, the yield and the crystallinity for synthesis of carbon nanotubes were manipulated by the selection of the catalyst.

Impact of the distance of light curing on the degree of conversion and microhardness of a composite resin

Objective. This study evaluated the impact of the distance between the light guide tip of the curing unit and material surface on the degree of conversion and Knoop microhardness of a composite resin. Materials and methods. Circular samples were carried out of a methacrylate micro-hybrid resin-based composite and light cured at 0, 2 and 4 mm distance. Monomer conversion rate was measured using a Fourier-transform Raman spectrometer and Knoop hardness number was obtained using a microhardness tester on the top and bottom surfaces. Data were statistically analyzed by analysis of variance and Tukey’s test (α = 0.05). Results. Overall, the increase of curing distance reduced the microhardness (p ≤ 0.05), but did not influence the carbon double bond conversion rate (p > 0.05) of the composite resin tested; and the top surface showed better properties compared to the bottom (p ≤ 0.05). Conclusions. The light curing at distance can reduce mechanical properties and could affect long-term durability of the composite restorations. Thus, the use of a curing device with high irradiance is recommended.

Vibrational spectroscopic and DFT calculation studies of 2-amino-7-bromo-5-oxo-[1]benzopyrano [2,3-b]pyridine-3 carbonitrile

The vibrational spectra of 2-amino-7-bromo-5-oxo-[1]benzopyrano [2,3-b]pyridine-3 carbonitrile were recorded using fourier transform-infrared and fourier transform-Raman spectrometer. The optimized structural parameters, vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals, thermodynamic properties, temperature dependence of thermodynamic parameters, first order hyperpolarizability and natural bond orbital calculations of the molecule were performed using the Gaussian 09 program. The vibrational frequencies were assigned on the basis of potential energy distribution calculation using the VEDA 4.0 program. The calculated first order hyperpolarizability of ABOBPC molecule was obtained as 6.908×10−30 issue, which was 10.5 times greater than urea. The nonlinear optical activity of the molecule was also confirmed by the frontier molecular orbitals and natural bond orbital analysis. The frontier molecular orbitals analysis shows that the lower energy gap of the molecule, which leads to the higher value of first order hyperpolarizability. The natural bond orbital analysis indicates that the nonlinear optical activity of the molecule arises due to the π→π∗ transitions. The Mulliken atomic charge distribution confirms the presence of intramolecular charge transfer within the molecule. The reactive site of the molecule was predicted from the molecular electrostatic potential contour map. The values of thermo dynamic parameters were increasing with increasing temperature.

Structure and Vibrational Modes of As-S-Se Glasses: Raman Scattering and Ab Initio Calculations

Samples of As18SxSe82-x glasses were prepared by conventional melt-quenching techniques with As, S and Se of 99.99% purity. Raman spectra of samples were obtained by a Fourier transform Raman spectrometer. In addition, all calculations based on Hartree-Fork theory have been used to investigate the Raman-active modes of AsSnSe3-n clusters. It can be found that the calculated data of basic cluster models are in excellent agreement with observed Raman spectra. We give an explanation about the Raman shift of main vibrational modes in AsSnSe3-n clusters.

The Fungal Phytochrome FphA from Aspergillus nidulans

The red light-sensing photoreceptor FphA from Aspergillus nidulans is involved in the regulation of developmental processes in response to light. Here we present extended biochemical and spectroscopic characterization of recombinant FphA using a synthetic gene with host-adapted codon usage. The recombinant photosensory domain FphAN753 was shown to display all features of a bona fide phytochrome. It covalently binds biliverdin as chromophore and undergoes red/far-red light-inducible photoconversion with both parent states being protonated. The large N-terminal variable extension of FphA exerts a stabilizing effect on the active Pfr state. Upon substitution of the highly conserved histidine 504, involved in the hydrogen-bonding network of the protein moiety and the chromophore, chromophore attachment and photoreversibility were completely impaired. FphA is a functional sensor histidine kinase with a strong red-light-dependent autophosphorylation activity. Furthermore, intermolecular trans-phosphorylation to the response regulator domain of a second monomer could be demonstrated. Interestingly, co-incubation of FphA and FphA variants led to enhanced autophosphorylation, including the "inactive" Pr form. The latter observed phenomenon might suggest that auto- and trans-phosphorylation activity is modulated by additional interaction partners leading to variable phosphorylation events that trigger a specific output response.

Optimization of Chemical Vapor Deposition Synthesis Conditions for Multiwall Carbon Nanotube by Statistical Analysis of Experiment

The optimization of chemical vapor deposition synthesis conditions for multiwall carbon nanotubes (MWCNTs) was experimentally investigated. Carbon nanotubes were grown on cobalt substrate thicknesses of 20, 100 and 1000 nm at 700 and 900 0C with 2 replications. The configuration and morphology of the carbon nanotubes were investigated by scanning electron microscope and Fourier transform raman spectrometer, respectively. The tendency of the parameters was evaluated by statistical design of experiment. Observations on samples produced under our optimised production process, showed that a large number of MWCNTs bundles were produced. Diameter of MWCNTs bundles ranges between 30 and 100 nm throughout the samples. From the variance analysis of the Raman spectra we observe that the thickness of cobalt and temperature of synthesis are highly significant in which the coherence length and innermost diameter increase for either the thickness increases or the temperature decreases.

Raman Spectra from Pesticides on the Surface of Fruits

Raman spectra of several vegetables and fruits were studied by micro-Raman spectrometer (514.5 nm) and Near-infrared Fourier Transform Raman spectrometer (FTRaman). It is shown that at 514.5 nm excitation, most of the spectra are from that of carotene with some very strong fluorescence in some cases. While at 1064 nm wavelength excitation, the spectra from the different samples demonstrate different characteristic Raman spectra without fluorescence. We discuss the spectroscopic difference by the two excitation wavelengths, and the application of Raman spectra for detection of pesticides left on the surface of vegetables and fruits. Raman spectra of fruits and pesticides were successfully recorded, and using the FT-Raman spectra the pesticides left on the surface of the fruits can be detected conveniently.

Fiber optic near-infrared Raman spectroscopy for clinical noninvasive determination of water content in diseased skin and assessment of cutaneous edema

Currently, measuring Raman spectra of tissues of living patients online and in real time, collecting the spectra in a very short measurement time, and allowing diagnosis immediately after the spectrum is recorded from any body region, are specific advantages that fiber optic near-infrared Raman spectroscopy (NIR RS) might represent for in vivo clinical applications in dermatology. We discuss various methodological aspects and state of the art of fiber optic NIR RS in clinical and experimental dermatology to outline its present advantages and disadvantages for measuring skin in vivo, particularly its water content. Fiber optic NIR Fourier transform (FT) RS has been introduced to dermatological diagnostics to obtain information regarding the molecular composition of the skin up to several hundred micrometers below the skin surface in a relatively fast nondestructive manner. This has been especially important for probing for in vivo assessment of cutaneous (intradermal) edema in patients patch test reactions. Fiber optic NIR FT Raman spectrometers still require further technological developments and optimization, extremely accurate water concentration determination and its intensity calculation in skin tissue, and for clinical applications, a reduction of measurement time and their size. Another promising option could be the possibility of applying mobile and compact fiber optic charge-coupled device (CCD)-based equipment in clinical dermatology.

On-line monitoring of airborne chemistry in levitated nanodroplets: in situ synthesis and application of SERS-active Ag-Sols for trace analysis by FT-Raman spectroscopy.

We report a new strategy for on-line monitoring of chemical reactions in ultrasonically levitated, nanoliter-sized droplets by Raman spectroscopy. A flow-through microdispenser connected to an automated flow injection system was used to dose picoliter droplets into the node of an ultrasonic trap. Taking advantage of the flow-through characteristics of the microdispenser and the versatility of the automated flow system, a well-defined sequence of reagents could be injected via the microdispenser into the levitated droplet placed in the focus of the collection optics of the Fourier transform Raman spectrometer. In that way, chemical reactions could be carried out and monitored on-line. The developed system was used for fast, reproducible, in situ synthesis of a highly active surface enhanced Raman scattering (SERS) sol resulting from the reduction of silver nitrate with hydroxylamine hydrochloride in basic conditions. With this chemical system, SERS substrate preparation could be achieved at room temperature and in short time. The in situ prepared silver sol was used for trace analysis of several organic test molecules that were injected into the levitated SERS-active droplet again using the microdispenser. The concentration dependence of the SERS spectra was studied using 9-aminoacridine, revealing that down to the femtogram region high-quality SERS spectra could be obtained. Additionally, SERS spectra of 6-mercaptopurine, thiamine, and acridine were recorded in the levitated drop as well.

AOTF Raman spectrometer for remote detection of explosives

A spectrometer based on acousto-optic tunable filters is developed for use in measuring Raman spectra as part of a detection system that is low-cost, reliable, and field-portable. The system is coupled with a fiber optic bundle to carry the excitation laser light to the sample and to collect the Raman scattered light. Spectra of the explosives trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX) and nitroguanidine (NQ) were obtained in very short times and are in good agreement with those taken with conventional Fourier transform Raman spectrometers. Spectra of mixtures of explosives were also obtained and show no overlap of their characteristic Raman bands.

Raman Spectroscopy with a Single-Frequency, High-Power, Broad-Area Laser Diode

A high-power, broad-area laser diode was used as an incident light source in a Raman spectrometer. The laser was forced to lase in a very narrow frequency range (⩽ 400 MHz) by the use of a Metcalf–Littman arrangement. All side bands and light-emitting diode (LED) modes were suppressed; their intensities are lower than the noise of recorded rotational spectra. The incident wavelength was tuned to coincide with the D1 transition of 85Rb. Due to this choice, the elastically scattered light (Rayleigh component) can be eliminated by a Rb cell in front of the spectrometer. The usefulness of this arrangement is demonstrated for CO2, N2, and air. Because of the suppression of the dominating Rayleigh intensity, this setup is ideally suited for a Fourier transform Raman spectrometer.

Raman Spectral Estimation via Fast Orthogonal Search

A Fourier transform (FT) spectrometer measures the autocorrelation (interferogram) of radiation emitted from a source and estimates the optical power spectral density through application of the discrete Fourier transform (DFT) to the recorded interferogram. Although a widely used method, FT spectrometry suffers because its frequency resolution is limited to the sampling rate divided by the number of time-series data points. A large number of points are therefore required to resolve an optical spectrum properly. In this paper, it is shown that a noise-resistant technique known as fast orthogonal search (FOS) can be used to achieve accurate optical spectrum estimation. Further, it is shown that frequency accuracy comparable to the DFT applied to the full interferogram can be obtained with FOS even if the original interferogram is contaminated with noise and then reduced by a factor of up to 10 by irregularly spaced sampling. The FOS application presented here is for the estimation of Raman spectra from interferograms acquired with an FT Raman spectrometer.

Fourier transform surface-enhanced Raman scattering of C 70 on a roughened silver surface

The surface-enhanced Raman (SER) spectrum of C 70 measured on an electrochemically-roughened silver surface using a Fourier transform Raman spectrometer with near infrared excitation is reported. The spectrum is very similar to the normal Raman spectrum of C 70, indicating little or no interaction between the C 70 molecules and the silver surface. A detection limit of about 11 ng of C 70 was found. Comparison with previously reported SERS results for C 70 showed significant differences for near infrared excitation. In particular, the band near 455 cm −1 was very intense for near infrared excitation but weak for visible excitation, and the band 1564 cm −1 was, conversely, weak for near infrared excitation but very intense when visible excitation was used.

Determination of Octane Numbers and Reid Vapor Pressure of Commercial Petroleum Fuels Using FT-Raman Spectroscopy and Partial Least-Squares Regression Analysis

A Fourier transform Raman spectrometer was used to collect the Raman spectra of 208 commercial petroleum fuels. The individual motor and research octane numbers (MON and RON, respectively) were determined experimentally using the industry standard ASTM knock engine method. Partial least-squares regression analysis was used to build regression models which correlate the Raman spectra of 175 of the fuels with the experimentally determined values for MON, RON, and pump octane number (the average of MON and RON) of the fuels. Each of the models was validated using leave-one-out validation. The standard errors of validation are 0.415, 0.535, and 0.410 octane units for MON, RON, and pump octane number, respectively. By comparing the standard error of validation to the standard deviation for the experimentally determined octane numbers, it is evident that the accuracy of the Raman determined values is limited by the accuracy of the training set used in creating the models. The Raman regression models were used to predict the octane numbers for the fuels which were not used to build the models. The results compare favorably with the leave-one-outvalidation. Also, it is demonstrated that the experimentally determined Reid vapor pressures are highly correlated with the Raman spectra of the fuel samples and can be predicted with a standard error of 0.568 psi.

Design and Characterization of a Visible-Light Fourier Transform Raman Spectrometer

We demonstrate the feasibility of Fourier transform (FT) Raman spectroscopy with visible wavelength excitation through design, construction, and characterization of a visible-light FT-Raman spectrometer. Our motivation to explore this approach stemmed from the need for a versatile Raman spectrometer for use in a confocal scanning laser Raman microscope we built. We discuss the spectrometer design features which contribute to efficient and reliable microscope operation and evaluate the spectrometer performance on the basis of a series of measurements chosen because of their impact on confocal microscope function. The measurements include the acquisition of representative Raman spectra from both solids and liquids, a demonstration of the independence of resolving power from input aperture diameter, the measurement of the absolute spectrometer optical efficiency curve, and an evaluation of the short- and long-term spectrometer noise processes.