Raman Intensity Changes Research Articles

Theoretical Study of Raman Intensities of p-Nitroaniline in Different Solvent Conditions by Using a Reference Interaction Site Model Self-Consistent Field Explicitly Including Constrained Spatial Electron Density Distribution.

Raman spectroscopy is one of the most powerful tools to understand and characterize the states and structures of systems in several environments. To obtain highly accurate changes in Raman intensities of systems in solution, theoretical treatment, which can deal with not only the states and structures of systems but also the environment around molecules, proves to be significant. Hence, in this study, we developed the calculation of changes in Raman intensities of systems in different solvent conditions by using the reference interaction site model self-consistent field study explicitly including constrained spatial electron density distribution; this model is designed based on elements from both quantum mechanics and statistical mechanics. We showed that our calculation method could reproduce the changes in Raman intensities of p-nitroaniline (pNA) under different solvent conditions, including supercritical water, which has been observed in previous experimental studies. Based on the analysis of the calculation results, we observed that the ratio of the Raman intensity change of pNA in different solvent conditions is strongly correlated with the charge-transfer character of pNA.

Multilayered Bioorthogonal SERS Nanoprobes Selectively Aggregating in Human Fluids: A Smart Optical Assay for β-Amyloid Peptide Quantification.

Alzheimer's disease (AD) is a debilitating neurological condition characterized by cognitive decline, memory loss, and behavioral skill impairment, features that worsen with time. Early diagnosis will likely be the most effective therapy for Alzheimer's disease since it can ensure timely pharmacological treatments that can reduce the irreversible progression and delay the symptoms. Amyloid β-peptide 1-42 (Aβ (1-42)) is considered one of the key pathological AD biomarkers that is present in different biological fluids. However, Aβ (1-42) detection still relies on colorimetric and enzyme-linked immunoassays as the gold standard characterized by low accuracy or high costs, respectively. In this context, optical detection techniques based on surface-enhanced Raman spectroscopy (SERS) through advanced nanoconstructs are promising alternatives for the development of novel rapid and low-cost methods for the targeting of Aβ pathological biomarkers in fluids. Here, a multilayered nanoprobe constituted by bioorthogonal Raman reporters (RRs) embedded within two layers of gold nanoparticles (Au@RRs@AuNPs) has been developed and successfully validated for specific detection of Aβ (1-42) in the human cerebrospinal fluid (CSF) with sensitivity down to pg/mL. The smart double-layer configuration enables us to exploit the outer gold NP surfaces for selective absorption of targeted peptide whose concentration controls the aggregation behavior of Au@RRs@AuNPs, proportionally reflected in Raman intensity changes, providing high specificity and sensitivity and representing a significant step ahead of the state of the art on SERS for clinical analyses.

Sensing of KCl, NaCl, and Pyocyanin with a MOF-Decorated Electrospun Nitrocellulose Matrix

Wearable sensors can provide important insight into a patient’s health status by monitoring the concentration of specific biomarkers in body fluids. Compared to biofluids such as blood or cerebrospinal fluid, which require an invasive acquisition process, other body fluids such as sweat or exhaled air can be easily collected using patches or masks, sufficient for the detection of metabolic and pathological changes. However, the successful integration of an efficient biosensor into textiles or polymer substrates is a challenge if flexibility and functionality are not to be compromised. Here, we demonstrate the integration of nanoporous metal–organic framework (MOF) particles with nitrocellulose (NC) fibrous layers using an electrospinning approach and validate the efficiency of our MOF@NC structure as biosensors. The chemical response of this hybrid nanomaterial upon exposure to different ionic sweat biomarkers such as NaCl and KCl as well as pyocyanin, a biomarker for the nosocomial pathogen Pseudomonas aeruginosa, was investigated using Raman spectroscopy. A change of the Raman intensity at distinct peaks of our MOF-containing architecture occurs after treatment of the material with the analyte solutions. Furthermore, we observed the sensitivities for pyocyanin at the normalized Raman intensity change to be up to −1120 au μm–1, about 4 orders of magnitude larger than for NaCl and KCl. The independence of our architecture from the type of MOF and the possibility of using different MOFs with individual chemistry make this approach a promising platform for versatile and adaptable sensing of biomarkers with high sensitivity and selectivity.

Classification of Systemic Lupus Erythematosus Using Raman Spectroscopy of Blood and Automated Computational Detection Methods: A Novel Tool for Future Diagnostic Testing.

The aim of this study was to explore the proof of concept for using Raman spectroscopy as a diagnostic platform in the setting of systemic lupus erythematosus (SLE). We sought to identify unique Raman signatures in serum blood samples to successfully segregate SLE patients from healthy controls (HC). In addition, a retrospective audit was undertaken to assess the clinical utility of current testing platforms used to detect anti-double stranded DNA (dsDNA) antibodies (n = 600). We examined 234 Raman spectra to investigate key variances between SLE patients (n = 8) and HC (n = 4). Multi-variant analysis and classification model construction was achieved using principal component analysis (PCA), PCA-linear discriminant analysis and partial least squares-discriminant analysis (PLS-DA). We achieved the successful segregation of Raman spectra from SLE patients and healthy controls (p-value < 0.0001). Classification models built using PLS-DA demonstrated outstanding performance characteristics with 99% accuracy, 100% sensitivity and 99% specificity. Twelve statistically significant (p-value < 0.001) wavenumbers were identified as potential diagnostic spectral markers. Molecular assignments related to proteins and DNA demonstrated significant Raman intensity changes between SLE and HC groups. These wavenumbers may serve as future biomarkers and offer further insight into the pathogenesis of SLE. Our audit confirmed previously reported inconsistencies between two key methodologies used to detect anti-dsDNA, highlighting the need for improved laboratory testing for SLE. Raman spectroscopy has demonstrated powerful performance characteristics in this proof-of-concept study, setting the foundations for future translation into the clinical setting.

Observation of the Pockels Effect in Ionic Liquids and Insights into the Length Scale of Potential-Induced Ordering.

Ionic liquids (ILs) under electric fields play essential roles in the electrochemical utilization of ILs. Recently, long-range organization of ILs in the vicinity of charged (and even neutral) surfaces has been revealed, but experimental evidence for such an ordering is still limited and its spatial length scale remains controversial. Here, we use confocal Raman microspectroscopy to investigate the effect of an applied electric potential on the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and its analogues in a space-resolved manner. Much to our surprise, the observed Raman difference spectra of the ILs obtained with and without an applied potential exhibit uniform intensity changes independent of vibrational modes of cations and anions, a finding in sharp contrast with the electric field effects on molecular liquids that we have previously observed. We interpret this unexpected finding in terms of the Pockels effect that occurs as a result of a potential-induced ordering of the IL near an IL-electrode interface. The refractive index changes due to the applied potential are estimated using the experimental Raman intensity changes. The results allow us to deduce that the length scale of the ordering in the ILs is tens to hundreds of nanometers, extending more than would be expected for the electrical double layer but not as far as a micrometer scale.

Examining the effect of exposure time on the erosive potential of sour candy

This study aimed to evaluate the erosive potential of sour candy at a different time of exposure within a laboratory-based setting. Fifty human anterior tooth samples were randomly assigned into three groups, namely: sour candy, regular candy A, and deionized water (n=15). Each tooth sample was exposed to a solution containing the sample groups at different time intervals. Vickers hardness tester was used to measure the surface hardness pre- and postexposure. The mean surface hardness value measured was compared using a paired sample test (α =.05). Raman spectroscopy was used to study the change in the enamel structure in all sample groups. A significant difference in the surface hardness value was measured pre and post-exposure in all the sample groups (P<0.01). The samples exposed to sour candy had the highest tooth surface loss. In terms of the time of exposure, it was found that prolonged exposure had a significant effect on the surface hardness (P<0.01). The Raman intensity change confirmed that samples exposed to sour candy, after 2 hrs of exposure, had the highest loss of structural integrity. The study conclude that sour candies are very erosive and its impact enhances with time.

Fermi resonance: A new way to investigate the planarization of p-quaterphenyl under high pressure

High pressure Synchrony X-ray diffraction (XRD) and Raman measurement of p-quaterphenyl has been carried out up to 13 GPa. There is no first-order phase transition from the XRD measurement but there are noticeable changes induced by pressure in the structural and vibrational properties. By analysis the Raman intensity changes of I1280/I1220, the dihedral angle between phenyl rings is decreased to a constant value when the pressure increased to 4 GPa, while less information could be concluded on further compression. Fermi resonance doublets located at 1600 and 1610 cm−1 were analyzed which suggests p-quaterphenyl undergo another process of molecular planarization at 8 GPa, providing a new strategy to evaluate the coplanar characteristics in OPPs system.

In vitro remineralization of enamel white spot lesions with a carrier-based amorphous calcium phosphate delivery system.

To achieve in vitro remineralization of enamel white spot lesions (WSLs) via a mesoporous delivery system of amorphous calcium phosphate (ACP) precursors. Amine-functionalized expanded pore mesoporous silica (aMSN) was loaded with polyacrylic acid-stabilized amorphous calcium phosphate (PAA-ACP) to develop a carrier-based delivery system (PAA-ACP@aMSN). Thirty-six artificial WSLs samples were created and randomly assigned to three treatments: artificial saliva solution (negative control, n = 12), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) slurry (n = 12), and PAA-ACP@aMSN slurry (n = 12). Surface microhardness, Raman intensity, and color were measured before/after artificial demineralization and after remineralization treatments to evaluate the remineralization level of each sample. SEM images were taken on the surface and cross-section of samples to observe microstructure changes. The surface microhardness recovery ratio (%SMHRR), Raman intensity change ratio (%ICR), and color recovery ratio (%CRR) were not significantly different between CPP-ACP and PAA-ACP@aMSN groups (P > 0.05), but both of them had significantly higher %SMHRR, %ICR, and %CRR values than negative control (P < 0.01). SEM images showed that apparent enamel prism imprints and inter-prism gaps in negative control were masked by mineral deposition in the PAA-ACP@aMSN and CPP-ACP groups. PAA-ACP@aMSN has an ability to remineralize enamel WSLs. The carrier-based amorphous calcium phosphate delivery system has great potential to serve as a remineralizing agent for the treatment of WSLs.

Multiplex Immunochips for High-Accuracy Detection of AFP-L3% Based on Surface-Enhanced Raman Scattering: Implications for Early Liver Cancer Diagnosis.

α-Fetoprotein (AFP) is an important tumor biomarker. In particular, the overexpression of AFP-L3 is associated with hepatocellular carcinoma (HCC). Accordingly, several hospitals have begun to employ the ratio of AFP-L3 to the total AFP level (AFP-L3%) as new diagnostic evidence for HCC owing to its high diagnostic accuracy. However, current methods of detection for AFP and AFP-L3 are time-consuming, require multiple samples, and lack in sensitivity and specificity. Herein, we present a novel concept for the early diagnosis of HCC based on the combination of Raman frequency shift and intensity change, and developed surface-enhanced Raman scattering (SERS)-based immunochips via AFP-L3%. In the first step of the study, the frequency shift of 4-mercaptobenzoic acid (MBA) was applied for the quantitative determination of total AFP based on the AFP and anti-AFP interaction on MBA-modified silver chips. 5,5-Dithiobis(succinimidyl-2-nitrobenzoate) (DSNB)-modified immunogold was then incorporated with AFP-L3 antibodies for sandwich immunoreaction on the chips. As a result, we found that a typical Raman band intensity of DSNB presented an exponential linear relationship with the concentration of AFP-L3. Thus, the AFP-L3% can be calculated according to the concentrations of AFP-L3 and total AFP. The most important advantage of the proposed method is the combination of AFP-L3% and frequency shifts of SERS, which exhibits excellent reproducibility and high accuracy, and significantly simplifies the conventional detection procedure of AFP-L3%. Application of the proposed method with the serum of patients with HCC demonstrated its great potential in early liver cancer diagnosis.

Raman intensity and vibrational modes of armchair CNTs

Raman intensity changes and frequency patterns have been studied using the various armchair (n,n) to understand the variations of bond polarizability, in regard to changing diameters, lengths, and the number of atoms in the (n,n). The Raman intensity trends of the (n,n) are validated by those of Cn isomers. For frequency trends, similar frequency patterns and frequency inward shifts for the (n,n) are characterized. Also, VDOS trends of the (n,n) expressing Raman modes are interpreted. The decomposition of vibrational modes in the (n,n) into radial, longitudinal, and tangential mode is beneficially used to recognize the distinct characteristics of vibrational modes.

The influence of size effect on interface phonons in core-shell quantum dot: a resonant Raman study

In this paper, the interface phonons in a core-shell quantum dot are theoretically studied by a resonant Raman scattering (RRS) process. Fröhlich electron–phonon interaction is considered in the framework of the dielectric continuum approach. The Raman peaks are found to be sensitive to the size of strongly confined shell. The shift of the Raman resonant peaks is a consequence of the change of observed dispersion of the phonon frequency. The Raman intensity changes in the system with shell thickness, originating from the competition between the spacial distribution of electron wave function and the number of phonons joining in the RRS process. The analysis of the Raman spectra gives a physical explanation to the size-selective nature of the Raman process and some experimental results.

Low Temperature Growth and Optical Properties of Zinc Oxide Nanostructure Prepared by Two-Step Solution-Based Deposition Method

ZnO thin films with typical c-axis (0 0 2) orientation were successfully deposited on glass substrates by two-step deposition method; mist-atomization and solution-immersion. The samples were annealed at selected temperature range of 350-500 ᵒC. The prepared samples then analyzed by Raman spectroscopy and photoluminescence (PL) spectroscopy. The optical properties of the samples were studied. The results of different annealing temperatures are also compared to investigate the optical and physical properties of each sample. Photoluminescence (PL) spectra showed low intensity in UV emission and high intensity in the visible emission, which indicates a good surface morphology of the ZnO nanorod. The Raman intensity changes in all sample were also tested.

Synthesis and Photoresponse of Large GaSe Atomic Layers

We report the direct growth of large, atomically thin GaSe single crystals on insulating substrates by vapor phase mass transport. A correlation is identified between the number of layers and a Raman shift and intensity change. We found obvious contrast of the resistance of the material in the dark and when illuminated with visible light. In the photoconductivity measurement we observed a low dark current. The on-off ratio measured with a 405 nm at 0.5 mW/mm(2) light source is in the order of 10(3); the photoresponsivity is 17 mA/W, and the quantum efficiency is 5.2%, suggesting possibility for photodetector and sensor applications. The photocurrent spectrum of few-layer GaSe shows an intense blue shift of the excitation edge and expanded band gap compared with bulk material.

Single-Walled Carbon Nanotubes Probing the Denaturation of Lysozyme.

Resonance Raman spectroscopy measurements of lysozyme-bound single-walled carbon nanotubes have been made during different stages of the chemically and thermally induced misfolding and of the denaturation process of nanotube-bound lysozymes. Changes to the Raman intensity of single-walled carbon nanotubes (SWNTs) have been observed during the denaturation of lysozyme. The Raman intensity changes are attributed to excitonic transition energy (Eii ) shifts of the SWNTs during the denaturation of lysozyme. The Eii shift of SWNTs was confirmed by photoluminescence measurements.

Pressure-induced depolarization and resonance in Raman scattering of single-crystalline boron carbide

We report polarized and resonant Raman scattering of single-crystal boron carbide $({\text{B}}_{4}\text{C})$ at high pressures. Significant intensity enhancements of 270 and $1086\text{ }{\text{cm}}^{\ensuremath{-}1}$ Raman bands of ${\text{B}}_{4}\text{C}$ have been observed at quasihydrostatic pressures higher than $\ensuremath{\sim}20\text{ }\text{GPa}$. The pressure-induced intensity change of the $1086\text{ }{\text{cm}}^{\ensuremath{-}1}$ band is mainly due to the resonance between excitation energy and electronic transition, whereas the intensity change of $270\text{ }{\text{cm}}^{\ensuremath{-}1}$ band is caused by the depolarization effect. Importantly, the first-order phase transition has not been found at high quasihydrostatic pressures and all the Raman intensity changes along with the corresponding high-pressure lattice distortion can be recovered during unloading.

Simple transformation of spectra to effectively reduce quantification errors in FT-Raman multivariate analysis of complex systems

Raman spectroscopy enables fast and reliable quantification of multi-component systems including pharmaceuticals. However, some experimental factors, such as changes in the exciting and scattering geometries, the position of the sample and the power of the exciting beam, can noticeably influence the accuracy and precision of this type of analysis. To avoid large analysis errors different techniques are applied. Among them, the ones known best are the internal or external standard method, standard normal variate (SNV) normalisation of spectra and multiplicative signal correction (MSC). Here we propose another simple and effective normalisation procedure, resulting in quantification errors below 1%, which originates from the fact that important experimental factors influencing Raman intensity change it in a multiplicative way (e.g., the power of the exciting beam or the sampling volume). FT-Raman spectra of a model 4-component mixture composed of cyclohexane, isooctane, toluene and p-xylene were normalised by I mean, the mean value of intensity calculated over the entire spectrum (MVN). From that we constructed a partial least squares (PLS) model that enabled more reliable quantification of components of the system in question as compared to PLS models based on SNV-normalised and MSC-corrected spectra. This procedure is extremely useful, for example, in the case of quantitative analysis based on FT-Raman measurements with changing incident laser power and the exciting or scattering geometry.

Resonant Raman Spectroscopy of Individual Strained Single-Wall Carbon Nanotubes

Resonance Raman spectra of individual strained ultralong single-wall carbon nanotubes (SWNTs) are studied. Torsional and uniaxial strains are introduced by atomic force microscopy manipulation. Torsional strain strongly affects the Raman spectra, inducing a large downshift in the E2 symmetry mode in the G+ band, but a slight upshift for the rest of the G modes and also an upshift in the radial breathing mode (RBM). Whereas uniaxial strain has no effect on the frequency of either the E2 symmetry mode in the G+ band or the RBM, it downshifts the rest of the G modes. The Raman intensity change reflects the effect of these strains on the SWNT electronic band structure.

Initial Excited-State Structural Dynamics of Thymine Are Coincident with the Expected Photochemical Dynamics

To explore the excited-state structural dynamics of thymine, a DNA nucleobase, we measured the resonance Raman spectra of thymine in aqueous solution at wavelengths throughout the lowest-energy absorption band. Self-consistent analysis of the resulting resonance Raman excitation profiles and absorption spectrum using a time-dependent wave packet formalism yielded the excited-state structural dynamics. The photochemically relevant C=C stretching and C-H deformation vibrational modes were found to exhibit maximum resonance Raman intensity and structural change upon photoexcitation for thymine, suggesting that the initial dynamics of thymine lie along the photochemical reaction coordinate.

A new quantitative Raman measurement scheme using Teflon as a novel intensity correction standard as well as the sample container

AbstractA novel and reliable quantitative Raman measurement scheme has been proposed for the analyses of ethanol and isopropanol solutions. Teflon tubing was employed as an effective intensity correction standard as well as the sample cell. This allowed for the synchronous collection of the mixed Raman spectrum from the Teflon standard and the sample without any extra optical configuration. A non‐overlapping Teflon band was used as the standard peak to correct the Raman intensity changes resulting from laser power variations. In addition to the use of Teflon tubing,a wide area illumination (WAI) scheme was employed, which made the laser illumination into a circle of 6 mm diameter (area: 28.7 mm2), to cover a wide sample area. The WAI scheme improved the reliability of the Raman measurement by significantly increasing the reproducibility of the sampling owing to a decreased sensitivity to sample placement with respect to the focal plane as well as a wider sample coverage area. The resulting Raman spectra were more reproducible and more representative of the correct sample composition. Overall, a superior prediction performance was achieved using the WAI scheme compared to the conventional Raman collection method. The proposed system has great potential for use in the quantitative analysis of diverse liquid samples with good reproducibility. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Low frequency Raman scattering of amorphous [formula omitted

Amorphous Ge 1−x S x (0.0⩽x⩽0.62) films were prepared by a laser ablation method, and their low frequency Raman scattering spectra were measured at 20 K. Two distinct vibration regimes were observed in the spectra. In the regime at higher frequencies, the power-law dependence of the reduced Raman intensity ( I∝ ω t ) changes with an increase in x for x>0.2 in such a way that t increases from 1.4 to 1.7 as x increases from 0.2 to 0.62. By applying a fracton model, the fractal dimension is found to decrease with an increase in x over the range 0.2⩽ x⩽0.62.