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Discrimination between enantiomers is achieved by tip-enhanced Raman scattering (TERS) using a silver tip that is chemically modified by an achiral para-mercaptopyridine (pMPY) probe molecule. Differences in the relative intensities of the pMPY spectra were monitored for three pairs of enantiomers containing hydroxy (-OH) and/or amino (-NH2 ) groups. The N: or N+ -H functionality of the pMPY-modified tip participates in hydrogen-bond interactions with a particular molecular orientation of each chiral isomer. The asymmetric arrangement of silver atoms at the apex of the tip induces an asymmetric electric field, which causes the tip to become a chiral center. Differences in the charge-transfer (CT) states of the metal-achiral probe system in conjunction with the asymmetric electric field produce different enhancements in the Raman signals of the two enantiomers. The near-field effect of the asymmetric electric field, which depends on the number of analyte functional groups capable of hydrogen-bond formation, improves the degree of discrimination.

An intensive analysis of far-infrared (far-IR), low-frequency Raman, and wide angle X-ray diffraction (WAXD) data has been performed by two-dimensional correlation spectroscopy (2D-COS) as a function of the blend ratio of poly(3-hydroxybutyrate)/poly(4-vinylphenol) (PHB/PVPh). Homospectral 2D-COS revealed that a weak band at 128 cm(−1) in the far-IR spectra appeared more clearly in the 2D correlation spectra. Heterospectral 2D-COS (far-IR/low-frequency Raman and far-IR/WAXD) provided very important results that were hardly detected in the conventional 2D-COS. A far-IR peak at 130 cm(−1) in the heterospectral 2D-COS had negative correlations with the peaks in the low-frequency Raman spectra at 81, 100, and 110 cm(−1) and WAXD profile 8.78 and 11.01°. These results indicated that those peaks have different origins; the 130 cm(−)1 peak comes from the intermolecular C=O···H–O hydrogen bond between PHB and PVPh, while those for low-frequency Raman and WAXD peaks are the features of PHB crystalline structure.

The purpose of this review is to demonstrate advances, challenges and perspectives of quantum chemical approaches in molecular spectroscopy of the condensed phase. Molecular spectroscopy, particularly vibrational spectroscopy and electronic spectroscopy, has been used extensively for a wide range of areas of chemical sciences and materials science as well as nano- and biosciences because it provides valuable information about structure, functions, and reactions of molecules. In the meantime, quantum chemical approaches play crucial roles in the spectral analysis. They also yield important knowledge about molecular and electronic structures as well as electronic transitions. The combination of spectroscopic approaches and quantum chemical calculations is a powerful tool for science, in general. Thus, our article, which treats various spectroscopy and quantum chemical approaches, should have strong implications in the wider scientific community. This review covers a wide area of molecular spectroscopy from far-ultraviolet (FUV, 120–200 nm) to far-infrared (FIR, 400–10 cm−1)/terahertz and Raman spectroscopy. As quantum chemical approaches, we introduce several anharmonic approaches such as vibrational self-consistent field (VSCF) and the combination of periodic harmonic calculations with anharmonic corrections based on finite models, grid-based techniques like the Numerov approach, the Cartesian coordinate tensor transfer (CCT) method, Symmetry-Adapted Cluster Configuration-Interaction (SAC-CI), and the ZINDO (Semi-empirical calculations at Zerner's Intermediate Neglect of Differential Overlap). One can use anharmonic approaches and grid-based approaches for both infrared (IR) and near-infrared (NIR) spectroscopy, while CCT methods are employed for Raman, Raman optical activity (ROA), FIR/terahertz and low-frequency Raman spectroscopy. Therefore, this review overviews cross relations between molecular spectroscopy and quantum chemical approaches, and provides various kinds of close-reality advanced spectral simulation for condensed phases.

This study aims at exploring the potential of ATR-far-ultraviolet (FUV) spectroscopy in investigating electronic structure and transitions of various kinds of biological molecules. For this purpose, ATR-FUV spectra were measured for several kinds of proteins with the different secondary structures, several kinds of carbohydrates, nucleic acids, and lipids. Band assignments have been made for all kinds of biological molecules investigated based on our previous ATR-FUV studies on n-alkanes, alcohols, esters, and amides. For example, the proteins show a characteristic band near 200 nm due to π-π* transition of amide groups. The position of this band varies a little with the secondary structure of proteins but its intensity changes significantly depending on the secondary structure and solutions. All the carbohydrates studied yielded a band near 170 nm due to n-Rydberg transition of ether. In addition, acetylcarbohydrates give an additional band near 190 nm originating from π-π* transition of amide at 2’ carbon. The present study has demonstrated that ATR-FUV spectroscopy is a new powerful technique in exploring electronic structure and transitions of biological molecules, in general. It is also possible to use ATR-FUV spectroscopy for quantitative and qualitative analysis of biological molecules. Moreover, it is of note that information regarding electronic transitions collected by ATR-FUV spectroscopy is useful for UV resonance Raman (UVRR) spectroscopy studies of biological molecules. A combined ATR-FUV spectroscopy and UVRR spectroscopy method may provide a novel analytical tool for molecular and electronic structure of biological molecules.

A remarkable enhancement of Raman scattering is achieved by submicrometer-sized spherical ZnO superstructures. The secondary superstructures of ZnO particles with a uniform diameter in the range of 220-490 nm was formed by aggregating ca. 13 nm primary single crystallites. By engineering the superstructure size to induce Mie resonances, leading to an electromagnetic contribution to the SERS enhancement. Meanwhile, a highly efficient charge-transfer (CT) contribution derived from the primary structure of the ZnO nanocrystallites was able to enhance the SERS signals as well. The highest Raman enhancement factor of 105 was achieved for a non-resonant molecule by the synergistic effect of CT and Mie resonances. The Mie resonances scattered near-field effect investigated in the present study provides not only an important guide for designing novel SERS-active semiconductor substrates, but also a coherent framework for modelling the electromagnetic mechanism of SERS on semiconductors.

Far-infrared (FIR) and low-frequency Raman bands in the 90–400 cm–1 region of crystalline nylon 6 in α form were assigned based on comparisons of experimental spectra and quantum mechanical calcula...

The νCN band (νC≡N) is a sensitive probe of the state of molecules with nitrile groups. Hence, physicochemical properties of acetonitrile and its derivatives have been frequently investigated by means of vibrational (IR and Raman) spectroscopy. Near-infrared (NIR) spectroscopy combined with high-level quantum mechanical calculations offers deeper physical insight into the structure of liquid nitriles not available from the fundamental region. This results from unique information provided by the overtones of νCN. Here, we report an application of anharmonic vibrational calculations coupled with IR, NIR, and Raman spectroscopy for investigation of the structure of CH3CN, CD3CN, and CCl3CN in the liquid phase. The computational part was based on generalized vibrational second-order perturbation theory (GVPT2) applied on the density function theory (B3LYP, M06-2X, and B2PLYP) level to monomers as well as linear and cyclic dimers. The obtained data were refined by counterpoise-corrected MP2 calculations to mimic the aggregation in the liquid state. Our results evidence that the intensity variations between the fundamental, first and second overtones of the νCN band depend on the symmetry of aggregated species. The symmetry of the cyclic dimers in liquid nitriles was elucidated from the relative intensity of the 2νCN band. This work advances our understanding of the vibrational spectra of acetonitrile and its derivatives by providing detailed band assignment of IR, NIR, and Raman spectra. For the first time, we reported the position of the first and second overtones of the nitrile group.

Here, we aimed to identify biomarkers for mice oocyte maturation in metaphase II in vivo and in situ using Raman spectroscopy. Principal component analysis of 324 Raman data points of oocytes at Phase I, II, III, and IV showed that the phosphoric acid concentration uniformly increased in oocytes with higher developmental competence than in oocytes at other maturation stages, and proteins were more phosphorylated. The maturation phases were successfully predicted by linear discriminant analysis with high accuracy (90.7%) using phosphoric molecular information mentioned above. Furthermore, detections of higher concentration of unsaturated fatty acids in overmatured oocytes indicated that a decline in metabolic activity due to overmaturation induced a surplus of these lipid components. Upon assessing invasiveness by laser irradiation, about 50% irradiated oocytes progressed to morula and blastocyst stages in good conditions. Thus, Raman spectroscopy holds promise in evaluating oocyte maturation and quality based on molecular information in infertility treatment.

Surface-enhanced Raman scattering (SERS) is a supersensitive technique for monitoring catalytic reactions. However, building a SERS-kinetics model to investigate catalytic efficiency on the surface or interface of the catalyst remains a great challenge. In the present study, we successfully obtained an excellent semiconducting SERS substrate, reduced MnCo

Amyloid fibrils are protein aggregates with needle-like morphology and cross-β structure that are associated with amyloidoses and neurodegenerative diseases. It is recently suggested that amyloid polymorphism, i.e., structural diversity of amyloid fibrils, has a deep relationship with pathology, attracting a great deal of attention for understanding molecular mechanism of amyloid diseases. However, its prompt recognition is almost halted due to inadequate development of analytical methods for detecting polymorphism of amyloid fibrils sensitively and quickly. Here, we propose that iodine staining, a coloring reaction that occurs by complexing iodine with host compounds to form polyiodide ions, can be used as a method for distinguishing polymorphs of amyloid fibrils. When three polymorphs of insulin fibrils, NaCl fibrils, SDS fibrils, and no-salt fibrils, were prepared and iodine-stained, they exhibited different colors. Furthermore, each of these colors was inherited to daughter fibrils by seeding reactions. The colors were fundamentally represented as a sum of three absorption bands in visible region between 400-750 nm, and these bands showed different titration curves against iodine, suggesting that there are more than one specific binding sites for the formation of polyiodide ions. The analysis of resonance Raman spectra and polarization microscope suggested the formation of several polyiodide species composed of I 3 - and/or I 5 - on the grooves or the edges of the β-sheets. It was concluded that the production of different polyiodide species and conformations are the molecular origin of the variation in colors depending on the surface structure of amyloid fibrils.

In fertilized fish eggs, lipids are an energy reservoir for the embryo development and substrate for organogenesis. They occur in the cytoplasmic area and form lipid droplets (LDs), but also the yolk egg is composed of lipids and proteins. Insight on the LD formation and distribution and their interactions with other cellular organelles could provide information about the role based on the egg development. For non-destructive, macro-scale visualization of biochemical components of fish eggs, such as lipids proteins and water, near-infrared (NIR) imaging is the method of choice. Mid-infrared (MIR) and Raman spectroscopy imaging were used to provide details on chemical composition of LDs and other egg organelles. NIR imaging illustrated main compartments of the egg including membrane, LDs, yolk, relative protein, and lipid content in well-localized egg structures and their interactions with water molecules. In the yolk, a co-existence of lipids and proteins with carotenoids and carbohydrates was detected by Raman spectroscopy. Results showed a prominent decrease of unsaturated fatty acids, phospholipids, and triglycerides/cholesteryl esters content in the eggs due to the embryo development. An opposite trend of changes was observed by MIR spectroscopy for the glycogen, suggesting that consumption of lipids occurred with production of this carbohydrate. The comprehensive vibrational spectroscopic analysis based on NIR, MIR, and Raman imaging is a unique tool in studying in situ dynamic biological processes.

Protein research by near-infrared (NIR) spectroscopy stretches back more than 25 years, however, it has not been well established yet. One of the most difficult parts comes from the fact that the key bands for investigating protein secondary structure are the combination bands such as those due to a combination of N–H stretching vibration and amide II modes. This review provides some explanation of how one can correlate the combination modes with protein secondary structure using several examples. One of the most important advantages of NIR protein research is that one can explore a change in hydration as well as that in the protein secondary structure at the same time. It is rather difficult for IR and Raman spectroscopy to investigate them simultaneously. In this review, we outline characteristic features of NIR spectroscopy in protein research first, and then band assignments of NIR spectra of proteins are described. After that several examples of NIR studies of proteins are introduced. Finally, as examples of NIR imaging to protein research, recent studies on fish egg development are discussed.

The difference in Raman spectra for different excitation wavelengths (532 nm, 785 nm, and 1064 nm) was investigated to identify an appropriate wavelength for the quantitative analysis of carotenoids in tomatoes. For the 532 nm-excited Raman spectra, the intensity of the peak assigned to the carotenoid has no correlation with carotenoid concentration, and the peak shift reflects carotenoid composition changing from lycopene to β-carotene and lutein. Thus, 532 nm-excited Raman spectra are useful for the qualitative analysis of carotenoids. For the 785 nm- and 1064 nm-excited Raman spectra, the peak intensity of the carotenoid showed good correlation with carotenoid concentration; thus, regression models for carotenoid concentration were developed using these Raman spectra and partial least squares regression. A regression model designed using the 785 nm-excited Raman spectra showed a better result than the 532 nm- and 1064 nm-excited Raman spectra. Therefore, it can be concluded that 785 nm is the most suitable excitation wavelength for the quantitative analysis of carotenoid concentration in tomatoes.

We present a rapid switching system between a newly developed near-infrared (NIR) spectrometer and its imaging system to select the spot size of a diffuse reflectance (DR) probe. In a previous study, we developed a portable NIR imaging system, known as D-NIRs, which has significant advantages over other systems. Its high speed, high spectral resolution, and portability are particularly useful in the process of monitoring pharmaceutical tablets. However, the spectral accuracies relating to the changes in the formulation of the pharmaceutical tablets have not been fully discussed. Therefore, we improved the rapid optical switching system and present a new model of D-NIRs (ND-NIRs) here. This system can automatically switch the optical paths of the DR and NIR imaging probes, greatly contributing to the simultaneous measurement of both the imaging and spot. The NIR spectra of the model tablets, including 0–10% ascorbic acid, were measured and simultaneous NIR images of the tablets were obtained. The predicted results using spot sizes for the DR probe of 1 and 5 mm diameter, resulted in concentrations of R2 = 0.79 and 0.94, with root mean square errors (RMSE) of 1.78 and 0.89, respectively. For tablets with a high concentration of ascorbic acid, the NIR imaging results showed inhomogeneity in concentration. However, the predicted values for the low concentration samples appeared higher than the known concentration of the tablets, although the homogeneity of the concentration was confirmed. In addition, the optimal spot size using NIR imaging data was estimated to be 5–7 mm. The results obtained in this study show that the spot size of the fiber probe, attached to a spectrometer, is important in developing a highly reliable model to determine the component concentration of a tablet.

A simple and ultrasensitive surface-enhanced Raman scattering (SERS) assay for heparin detection has been demonstrated based on an in situ hot spot assembly method using N,N'-bis[3,3'-(trimethylammonium)propylamine]-3,4,9,10-perylenediimide (bis-quaternized perylene dye, abbreviated as BQPER). In this assay, a BQPER probe with two positive charges is employed as both Raman reporter and electrostatic bridge to cause the aggregation of citrate-capped Ag nanoparticles (Ag NPs), resulting in a strong SERS signal due to the formation of numerous hot spots in the gaps of the aggregates. The SERS intensity of BQPER decreases in the presence of heparin, because BQPER binds primarily to heparin due to its high anionic charge to mass ratio compared to that of Ag NPs. Accordingly, a novel method for the detection of heparin has been developed based on SERS of the unbound BQPER probe. Two obvious advantages of the proposed heparin assay over other reported methods are: its much wider linear concentration range (10-5-10-10 g mL-1) and lower limit of detection (0.08 ng mL-1). Besides, our proposed heparin assay has been successfully applied to the detection of heparin in serum samples, indicating its great potential in the diagnosis of heparin-related diseases. This work provides a new Raman probe for the SERS analysis of heparin and opens a different perspective for SERS-based transducer design in charged analytes.

Two-dimensional correlation spectroscopy (2DCOS) has been widely used to Infrared, Raman, Near IR, Optical Activity (ROA), Vibrational Circular Dichroism (VCD) and Fluorescence spectroscopy. In addition, several new developments, such as 2D hetero-correlation analysis, moving-window two-dimensional (MW2D) correlation, model based correlation (βν and kν correlation analyses) have also well incorporated into protein research. They have been used to investigate secondary structure, denaturation, folding and unfolding changes of protein, and have contributed greatly to the field of protein science. This review provides an overview of the applications of 2DCOS in the field of protein science for the past 20 year, especially to memory our old friend, Dr. Boguslawa Czarnik-Matusewicz, for her great contribution in this research field. The powerful utility of 2DCOS combined with various analytical techniques in protein studies is summarized. The noteworthy developments and perspective of 2DCOS in this field are highlighted finally.

Composition-, temperature-, and polarization-dependent low-frequency Raman and terahertz (far-infrared; FIR) spectra were measured for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) with PHB-type crystal structure and PHV-type crystal structure to investigate their intermolecular interactions. Band assignments were attempted by comparing the low-frequency Raman and terahertz (FIR) spectra of P(HB-co-HV) with the varying HV content with the corresponding spectra of PHB and by observing spectral variations. The spectra of P(HB-co-HV) (HV = 9, 15, and 21 mol%) are similar to the corresponding spectra of PHB. There are two bands at 97 and 82 cm−1 which are assigned to a spring type vibrational mode of the helical structure and to the mode reflecting the intermolecular interaction (CH3⋯O=C hydrogen bond), respectively. The low-frequency Raman and terahertz spectra of P(HB-co-HV) with HV content of 66 and 88.6 mol% show bands at 91 and 78 cm−1. The 78 cm−1 band is assigned to the intermolecular interaction (CH2⋯O=C hydrogen bond). In contrast to the 97 cm−1 band of P(HB-co-HV) with the low HV content, the 91 cm−1 band of P(HB-co-HV) with the high HV content show a temperature-dependent shift by 4 cm−1. Thus, although it seems that both 97 and 91 cm−1 bands are due to spring-like vibrational modes, the nature of two vibrational modes seems to be significantly different, reflecting the difference in the intermolecular interaction.

In this study, we have investigated the water absorption-induced structural changes and thermal behavior of e-poly(L)lysine-hydrochloride (EPLHCl) in the powder and film samples using infrared (IR) and Raman spectroscopy. An X-ray diffraction measurement reveals that the crystal structure of e-poly(L)lysine (EPL) is similar to that of the γ-crystal of nylon-6. The powder form of EPLHCl absorbs water from the air and solidifies into a film (18% water content). The film does not transform into the powder form with increasing temperature; it remains as a film, suggesting that the transformation from powder to film is irreversible. The IR spectra in the amide Ⅰ region of the powder and film are distinctly different, indicating that the secondary structure of EPLHCl changes upon water absorption. The position of the amide I band suggests that the powder form of EPLHCl has a β-sheet structure, while the film has two types of β-sheet structures. Raman spectra of EPLHCl in the region 1490–1440 cm−1 indicate that the EPLHCl film has a trans amide structure, unlike its powder form. Hence, it is highly probable that the differences in the secondary structures of the EPLHCl powder and film originate due to the twisting of the amide group induced by water absorption.

The significant worldwide expansion of the health food market, which includes functional fruits and vegetables, requires a simple and rapid analytical method for the on-site analysis of functional components, such as carotenoids, in fruits and vegetables, and Raman spectroscopy is a powerful candidate. Herein, we clarified the effects of Raman exposure time on quantitative and discriminant analysis accuracies. Raman spectra of intact tomatoes with various carotenoid concentrations were acquired and used to develop partial least squares regression (PLSR) and partial least squares discriminant analysis (PLS-DA) models. The accuracy of the PLSR model was superior (R2 = 0.87) when Raman spectra were acquired 10 s, but decreased with decreasing exposure time (R2 = 0.69; 0.7 s). The accuracy of the PLS-DA model was unaffected by exposure time (hit rate: 90%). We conclude that Raman spectroscopy combined with PLS-DA is useful for the on-site analysis of carotenoids in fruits and vegetables.

Ammonium nitrate (AN) is an important component of the chemical industry such as an active ingredient in fertilizers, as an oxidizer in explosive compositions and propellants, and as a blasting agent in civil explosives. Numerous accidents have been reported in the past which concerns its thermal instability and poses a big threat to its processing, transportation, and storage. Despite much literature being reported to understand its thermal instability, a mechanistic view remains unclear. In the present work, we have studied the behavior of AN to temperature change using a mathematical approach called 2D correlation (2D Cos) Raman spectroscopy to provide complete insight into the detailed dynamical nature of the interactions between the species (ionic or molecular) occurring with an increase in temperature. We have analyzed various libration and translational modes of nitrate in the low-frequency region using this mathematical tool. It is observed from 2D maps that the phase transition of AN starts with changes in libration modes followed by various nitrate modes and ammonium modes which further precedes low-frequency translational modes. Further, the 2D correlation could differentiate between modes splitting and shifting based on specific 2D Cos pattern. The changes occurring in the N-O deformation modes, symmetric stretching modes as well as anti-symmetric stretching modes which have been attributed to the weakening of the hetero-ionic coupling between the NH4+ and the NO3– ions could be clearly distinguished in the 2D synchronous and asynchronous plots. Besides, moving window analysis was performed to visualize the transition temperature at which phase change of AN takes place.

Cupric oxide leaf-like nanostructures (CuONSs) (average dimensions: 80-180 nm in width and 400-750 nm in length) were synthesized via anodic electrochemical dissolution of copper in an ethanol solution containing LiCl electrolyte and water. Ultraviolet-visible (UV-Vis), Fourier-transform infrared (FT-IR), and Raman spectroscopies as well as scanning electron microscope (SEM), high-resolution transmission electron microscopy with energy dispersive X-ray (HD-TEM-EDS), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) were used to explore the metal surface plasmon, size, rheology, and structure of CuONSs. Then, pyridine α-aminophosphinic acid isomers (α-, β-, and γ-NHPy) were synthesized and assembled on the CuONS/air and CuONS/aqueous solution interfaces at the pH level of solution = 7. Differences in adsorption and thus in the spectral response resulting from positional isomerism were examined by surface-enhanced Raman scattering (SERS) with an excitation wavelength of 785 nm. The manner of interaction of the investigated isomers with CuONSs in an aqueous solution was discussed in detail and compared with that at the CuONS/air interface. For γ-NHPy, at the CuONS/water interface, the time-dependent changes in the spectral profile were observed and analyzed. For β-NHPy at the CuONS/air interface, tip-enhanced Raman scattering (TERS) measurements were performed. These measurements allowed observing single molecule behavior and avoiding interference from the molecule's surrounding environment.

We aimed to investigate insulin amyloid fibril polymorphism caused by salt effects and heating temperature, and to visualize the structural differences of the polymorphisms in situ using Raman imaging without labeling. The time course monitoring for amyloid formation was carried out in an acidic condition without any salts and with two species of salts (NaCl and Na2SO4) by heating at 60, 70, 80, and 90 ℃. The intensity ratio of two Raman bands at 1672 and 1657 cm-1 due to β-sheet and α-helix structures was revealed to be an indicator of amyloid fibril formation, and the relative proportion of the β-sheet structure was higher in the case with salts, especially at a higher temperature and with Na2SO4. In conjunction with the secondary structural changes of proteins, the S-S stretching vibrational mode of a disulfide bond (∼514 cm-1) and the ratio of the tyrosine doublet R(I850⁄I826) were also found to be markers distinguishing polymorphisms of insulin amyloid fibrils by principal component analysis (PCA). Especially, amyloid fibrils with Na2SO4 media formed the g-g-g conformation of disulfide bond at a higher rate and without any salts; on the contrary, the g-g-g conformation was partially transformed into the g-g-t conformation at higher temperatures. The different environments of the hydroxyl groups of the tyrosine residue were assumed to be caused by fibril polymorphism. Raman imaging using these marker bands also successfully visualized the two- and three-dimensional structural differences of amyloid polymorphisms. The present results indicate the potential of Raman imaging as a diagnostic tool for polymorphisms in tissues of amyloid-related diseases.Statement of SignificanceOur results revealed three Raman markers distinguishing amyloid fibril polymorphisms caused by salt and temperature effects; the relative proportion of protein secondary structures (α–helix and β-sheet), the ratio of tyrosine doublet, and the conformational differences of disulfide bonds. The lower values of tyrosine doublet in the case with salts were interpreted as the anions rob the hydration water from proteins which induced protein misfolding. Using these parameters, Raman images captured their higher order structural differences in situ without labeling. The images of hydrogen bonds strength variations due to tyrosine doublet is believed to include significant novelty. The present results imply the potential of Raman imaging for use as a diagnostic imaging tool for tissues with amyloid-induced diseases.

Melamine (IUPAC: 1,3,5-Triazine-2,4,6-triamine) attracts high attention in analytical vibrational spectroscopy due to its misuse as a food adulterant. Vibrational spectroscopy [infrared (IR) and Raman and near-infrared (NIR) spectroscopy] is a major quality control tool in the detection and quantification of melamine content. The physical background for the measured spectra is not interpreted in analytical spectroscopy using chemometrics. In contrast, quantum mechanical calculations are capable of providing deep and independent insights therein. So far, the NIR region of crystalline melamine has not been studied by quantum mechanical calculations, while the investigations of its IR spectra have remained limited. In the present work, we employed fully anharmonic calculation of the NIR spectrum of melamine based on finite models, and also performed IR spectral simulation by using an infinite crystal model&mdash, periodic in three dimensions. This yielded detailed and unambiguous NIR band assignments and revised the previously known IR band assignments. We found that the out-of-plane fundamental transitions, which are essential in the IR region, are markedly more sensitive to out-of-plane inter-molecular interactions of melamine than NIR transitions. Proper description of the chemical surrounding of the molecule of melamine is more important than the anharmonicity of its vibrations. In contrast, the NIR bands mostly arise from in-plane vibrations, and remain surprisingly insensitive to the chemical environment. These findings explain previous observations that were reported in IR and NIR analytical studies of melamine.

Intrinsic properties of nickel have enabled its wide applications as an effective catalyst. In this study, nickel nanowires (Ni NWs) as electron donors for oxidized cytochrome c (Cyt c) are investigated, which are NW diameter, temperature, and pH value-dependent. The reductive and magnetic properties facilitate the Ni NWs to rapidly and conveniently reduce Cyt c in complicated biological samples. Moreover, we find that the Ni NWs combined with resonance Raman spectroscopy have specificity toward Cyt c detection in real biological samples, which is successfully used to distinguish the redox state of the released Cyt c from isolated mitochondria in apoptotic Hela cells. Moreover, rapid label-free Cyt c quantification can be achieved by surface-enhanced Raman spectroscopy with a limit of detection of 1 nM and long concentration linear range (1 nM-1 μM). The proposed Ni NWs-based reduction approach will significantly simplify the traditional biological methods and has great potential in the application of Cyt c-related apoptotic studies.

We aim to determine the relationship between the local crystalline structure of polyamide 6 (PA6) within carbon fibers (CFs) and the mechanical properties of unidirectional CF-reinforced PA6 composites. Two types of CFs with different surface profiles (one smooth and one rough), used as reinforcements, were employed for the transverse Charpy impact test of unidirectional PA6/CF composites. The surface profile of CF influenced the impact strength and debonding appearance. The crystalline structure of PA6 within CFs was investigated using micro-Raman spectroscopy with a spatial resolution of 1 μm. Based on the Raman study, it was suggested that the impact strength and debonding appearance were attributed to the varying polymorphism (α-phase, mesomorphic β-phase, and γ-phase crystal) of the PA6 matrix between the interface and locations away from the interface (i.e., the bulk region), depending on the surface profiles of CF.

The interactions of acrylic acid-based super absorbent polymers (SAPs) with water and the hydrogen bonding of water within its three-dimensional network were studied using Raman spectroscopy. The Raman spectra of SAP solutions suggested that both the COO− and CH2 groups of SAPs interact with water. The Raman spectra of pure water and those of SAPs containing approximately 40, 50, and 60% water exhibited a broad band corresponding to the OH-stretching mode of water in the 4000–3000 cm−1 region. This band was separated into three components using a curve-fitting method. The three components at 3200, 3400, and 3600 cm−1 were assigned to the OH-stretching modes of strong hydrogen bonding (SHB), weak hydrogen bonding (WHB), and dangling bond (Dang) species of water, respectively. The fractional areas of the three components were calculated and compared. The changes in the hydrogen bonding of water were compared with those of the water present in SAPs, and their temperature-dependent variations were elucidated. At a water content of approximately 60%, the behavior of the fractional area versus temperature was similar to that of pure water. However, at a water content of approximately 40%, the behavior was significantly different. The fraction of SHB was smaller, and the fraction of WHB was larger than that of pure water. The difference in the CH and COO− peak shifts of SAP, which is a result of the addition of a small percentage of water, was revealed by Raman spectroscopy. The position of the CH2 deformation peak changed linearly. However, the position of the COO− rocking peak did not change significantly up to a water content of 30%, above which it exhibited a rapid shift to lower wavenumbers. This result indicates that the interactions of the CH2 and COO− groups are different.

We aim to investigate the ordered polycarbonate (PC) structure around a reinforcement fiber and the interfacial properties of the interaction between PC and the reinforcement fiber. Pitch-based carbon fiber (piCF) and E-glass fiber (GF) were used as reinforcement fibers. From the results of the present Raman analysis of PC/piCF and PC/GF composite, we concluded that the interaction of the phenyl ring (π electrons) between PC and piCF is attributed to the formation of the ordered structure of PC at the piCF surface. In the case of the PC/GF composite, neither the interaction nor the formation of the ordered structure of PC is identified. It is confirmed that the interfacial shear strength of PC/piCF is higher than that of PC/GF. It is concluded that the interaction of π electrons between PC and piCF affects the interfacial shear strength.

3D surface-enhanced Raman scattering (SERS) imaging with highly symmetric 3D silver microparticles as a SERS substrate was developed. Although the synthesis method is purely chemical and does not involve lithography, the synthesized nanoporous silver microparticles possess a regular hexapod shape and octahedral symmetry. By using p-aminothiophenol (PATP) as a probe molecule, the 3D enhancement patterns of the particles were shown to be very regular and predictable, resembling the particle shape and exhibiting symmetry. An application to the detection of 3D inhomogeneity in a polymer blend, which relies on the predictable enhancement pattern of the substrate, is presented. 3D SERS imaging using the substrate also provides an improvement in spatial resolution along the Z axis, which is a challenge for Raman measurement in polymers, especially layered polymeric systems.

Titanium dioxide (TiO2) is a typical semiconductor metal oxide. It functions under irradiation with ultraviolet (UV, ≤400 nm), deep-ultraviolet (DUV, ≤300 nm), and far-ultraviolet (FUV, ≤200 nm) light. Therefore, investigations in these regions are essentially important not only for the basic understanding of the properties of TiO2 but also for the development of various applications such as photocatalysis and solar cells. In this review, the historic and recent research studies of TiO2 in these areas are overviewed. In particular, recent marked progress on attenuated total reflectance (ATR) DUV–FUV spectroscopy, resonant DUV Rayleigh scattering spectroscopy, and DUV Raman spectroscopy are focused on intensively. These pursuits provide detailed insights into the electronic states, bandgap energies, and phase transformations of TiO2 and TiO2 based materials as well as design guides for their applications.

Surface-enhanced resonance Raman scattering (SERRS) has been used to establish a rapid and quantitative assay based on the diazotization coupling reaction for thyrotropin-releasing hormone (TRH). Ultrahigh sensitivity of this approach originates from two factors: changing TRH to an azo compound and the SERRS effect with the addition of silver nanoparticles (AgNPs) at 532 nm excitation wavelength. The lowest detectable concentration of TRH was found to be as low as 1 pg mL(-1), which is 10-fold lower than the lowest normal reference value in human serum reported in previous literature. The quantitative measurements in human serum based on this method were conducted, and the results showed its feasibility for detection in complex biological samples. In comparison with conventional TRH identification and quantification methodologies, radioimmunoassay (RIA) and subsequent various hyphenated techniques, the main advantages of this study are simplicity, rapidness (2 minutes), time effectiveness, no additional steps required to further characterize the immunogenic material, highest sensitivity (57.1 fg), high selectivity, practicality and reliability. Thus, this work puts forward a research tool that may be applied to the determination of TRH in practical assays.

Surface-enhanced Raman scattering (SERS) is increasingly becoming an important analytical technique in various fields, which can mostly be attributed to the significant evolution of SERS-active substrates. The semiconductor-based SERS technique is particularly interesting because the inherent physicochemical properties of semiconductor materials offer several possibilities for the development and improvement of SERS-based analytical techniques. According to the effect of the semiconductor materials in SERS, semiconductor-based SERS techniques can be categorized into two areas: (1) semiconductor-enhanced Raman scattering, in which a semiconductor material is directly used as a substrate for enhancing Raman signals of adsorbed molecules, and (2) semiconductor-mediated-enhanced Raman scattering, in which a semiconductor is employed as an ‘antenna’ or ‘trap’ to modulate the Raman enhancement originating from a metal substrate. While the theory on semiconductor-based SERS is still incomplete and evolving, semiconductor-based SERS techniques have already resulted in substantial progress in biological analysis, photocatalysis, solar cells, sensing, and optoelectronic devices. The aim of this review is to outline the recent progress in this emerging research field, with a special emphasis on its analytical performance and application areas. Copyright © 2015 John Wiley & Sons, Ltd.

It is recently suggested that amyloid polymorphism, i.e., structural diversity of amyloid fibrils, has a deep relationship with pathology. However, its prompt recognition is almost halted due to insufficiency of analytical methods for detecting polymorphism of amyloid fibrils sensitively and quickly. Here, we propose that iodine staining, a historically known reaction that was firstly found by Virchow, can be used as a method for distinguishing amyloid polymorphs. When insulin fibrils were prepared and iodine-stained, they exhibited different colors depending on polymorphs. Each of the colors was inherited to daughter fibrils by seeding reactions. The colors were fundamentally represented as a sum of three absorption bands in visible region between 400 and 750 nm, and the bands showed different titration curves against iodine, suggesting that there are three specific iodine binding sites. The analysis of resonance Raman spectra and polarization microscope suggested that several polyiodide ions composed of I3− and/or I5− were formed on the grooves or the edges of β-sheets. It was concluded that the polyiodide species and conformations formed are sensitive to surface structure of amyloid fibrils, and the resultant differences in color will be useful for detecting polymorphism in a wide range of diagnostic samples.

To date, the main methods of texture measurement are sensory testing and instrumental testing. These two testing methods are time-consuming and often destructive respectively. In this study, Raman spectroscopy was used to predict the texture of different frozen/thaw raw beef from continuous freezing and repeated freeze-thaw treatments. The effect of repeated freeze-thaw treatment on beef texture was significantly different (p

The potential of a nanoporous Ag microstructure (np-AgMs) for use as a single particle for surface-enhanced Raman scattering spectroscopy (SERS), with the added advantages of being easy to manipulate and reusable, was successfully demonstrated. The np-AgMs with interconnected pore and controllable pore size were fabricated from symmetric hexapod AgCl via a galvanic replacement reaction in NaCl solution with zinc (Zn) as the sacrificed metal. The clean surface of np-AgMs enables rapid surface functionalization with easy handling and sample preparation as no particle aggregation occurs. The SERS acquisition spots on the np-AgMs can be visually selected using a normal Raman microscope. SERS spectra of p-aminothiophenol (PATP) with a concentration range of 10−8–10−3 M can be achieved. The position-dependent enhancement of np-AgMs was expendably evaluated. The signal-position correlation was confirmed by electric filed enhancement obtained from Finite-difference time-domain (FDTD) calculation. In addition, the highly stable substrate showed insignificant loss of the enhanced Raman signal after several cycles of chemical re-generation. Finally, the potential application of np-AgMs in label-free detection of biomolecules including hemoprotein, protein without chromophore and DNA strains at low concentration of 500 μg mL−1 was demonstrated.

Despite much effort to improve the design of surface-enhanced Raman spectroscopy (SERS) substrates, it remains a great challenge to develop a general substrate that can separate, enrich, and detect diverse targets in real environments. We demonstrate a novel three-dimensional (3D) superhydrophobic SERS substrate to detect polycyclic aromatic hydrocarbon (PAH) pollutants. The unique 3D superhydrophobic SERS substrate was produced by a galvanic replacement reaction between nickel foam and auric chloride acid, followed by modification with long-chain alkyl mercaptan molecules. Owing to the 3D micro-nanoscale hierarchical structure and long-chain alkyl mercaptan molecules, the as-prepared 3D Au nanoparticles/nickel foam (Au NPs/nickel foam) exhibited superhydrophobic properties, which may be used to detect PAHs due to the hydrophobic interactions. In SERS spectra with this substrate, pyrene could be detected at concentrations as low as 10−8 M. The enhancement factor of the 3D SERS substrate for pyrene detection was calculated to be about 1.2 × 104. This 3D hydrophobic SERS substrate enables the ultrasensitive detection of various analytes with poor affinity for adsorption on conventional SERS substrates, making SERS a potential and more widely practical analytical technique. Moreover, such 3D hydrophobic SERS substrates could be applied as an oil–water separation system for the separation, enrichment and sensitive detection of pollutants in real environments.

A simple and effective strategy for improving the accuracy of the multivariate determination of polyethylene (PE) density using Raman spectroscopy has been demonstrated. This strategy is based on the possibility that varied polymeric structures of the PE samples, especially at a sub-zero temperature range, would enhance their spectral selectivity, thereby potentially improving the multivariate correlation with their pre-determined physical properties such as density. For the evaluation, Raman spectra were collected at regular intervals during continuous increase of the PE temperature from cryogenic to near room temperature. Then, using partial least squares (PLS) regression, calibration models were developed to correlate the Raman spectral features collected at each time period with the reference PE density values. Interestingly, the accuracy was improved when the temperature of the PE pellets was -35 °C, near the glass transition temperature (Tg). To explain the improved accuracy, a two-dimensional (2D) correlation analysis was employed to detail the spectral variation induced by temperature change. Diverse segmental chain motions (so called micro-Brownian motion) predominantly occurring in the amorphous section of the PEs around Tg greatly enhanced the spectral selectivity among PE samples. In addition, minor β-relaxation occurring around this temperature was an additional source of the enhanced spectral selectivity. In parallel, differential scanning calorimetry (DSC) curves of the samples were also examined to check the existence of the phase transitions.

The present study investigates the structure of lycopene aggregates both in vitro and in vivo using ultraviolet–visible (UV–vis) and Raman spectroscopies. The electronic absorption bands of the J- and H-aggregates in vitro shift to lower and higher energies, respectively, compared to that of the lycopene monomer. Along with these results, the frequencies of the ν1 Raman bands were shifted to lower and higher frequencies, respectively. By plotting the frequencies of the ν1 Raman band against the S0 → S2 transition energy, a linear relationship between the data set with different aggregation conformations can be obtained. Therefore, the band positions depending on the different conformations can be explained based on the idea that the effective conjugated C═C chain lengths within lycopene molecules are different due to the environmental effect (site-shift effect) caused by the aggregation conformation. Applying this knowledge to the in vivo measurement of a tomato fruit sample, the relationship between the ...

In this study, a lycopene-content-based discriminant analysis was performed using a portable near-infrared-excited Raman spectrometer. In the vegetable-juice Raman spectra, the peak intensity of the lycopene band increased with increasing lycopene concentration, but scattering decreased the repeatability of the peak intensity. Consequently, developing a lycopene-concentration regression model using peak intensity is not straightforward. Therefore, a new method known as the product of mean intensity ratio (PMIR) analysis was developed to rapidly identify lycopene-rich samples on-site. In the PMIR analysis, Raman spectra are measured with short exposure times, confirming only the peaks of carotenoids with high concentrations, and thus the lycopene concentrations of vegetable juice samples could be determined successfully. Exposure times of 20ms and 100ms could detect lycopene concentrations of ≥5mg/100g and ≥2mg/100g with 93.2% and 97.7% accuracy, respectively; thus, lycopene-content-based discriminant analysis using the PMIR and a portable Raman spectrometer is feasible.

This study aimed to extract the paraffin component from paraffin-embedded oral cancer tissue spectra using three multivariate analysis (MVA) methods; Independent Component Analysis (ICA), Partial Least Squares (PLS) and Independent Component - Partial Least Square (IC-PLS). The estimated paraffin components were used for removing the contribution of paraffin from the tissue spectra. These three methods were compared in terms of the efficiency of paraffin removal and the ability to retain the tissue information. It was found that ICA, PLS and IC-PLS could remove the paraffin component from the spectra at almost the same level while Principal Component Analysis (PCA) was incapable. In terms of retaining cancer tissue spectral integrity, effects of PLS and IC-PLS on the non-paraffin region were significantly less than that of ICA where cancer tissue spectral areas were deteriorated. The paraffin-removed spectra were used for constructing Raman images of oral cancer tissue and compared with Hematoxylin and Eosin (H&E) stained tissues for verification. This study has demonstrated the capability of Raman spectroscopy together with multivariate analysis methods as a diagnostic tool for the paraffin-embedded tissue section.

Current research focuses on embryonic development and quality not only by considering fundamental biology, but also by aiming to improve assisted reproduction technologies, such as in vitro fertilization. In this study, we explored the development of mouse embryo and its quality based on molecular information, obtained nondestructively using Raman spectroscopy. The detailed analysis of Raman spectra measured in situ during embryonic development revealed a temporary increase in protein content after fertilization. Proteins with a β-sheet structure—present in the early stages of embryonic development—are derived from maternal oocytes, while α-helical proteins are additionally generated by switching on a gene after fertilization. The transition from maternal to embryonic control during development can be non-destructively profiled, thus facilitating the in situ assessment of structural changes and component variation in proteins generated by metabolic activity. Furthermore, it was indicated that embryos with low-grade morphology had high concentrations of lipids and hydroxyapatite. This technique could be used for embryo quality testing in the future.

Low-frequency vibrational modes of lamellar crystalline poly(glycolic acid) (PGA) were measured on Raman and far-infrared (FIR) spectra. Among the observed bands, an FIR band at ∼70 cm–1 and a Raman band at 125 cm–1 showed a gradual lower-frequency shift with increasing temperature from 20 °C to the melting point at ∼230 °C. Their polarization direction was perpendicular to the chain axis of PGA. Both spectra were quantum-mechanically simulated with the aid of a fragment method, the Cartesian-coordinate tensor transfer, which enabled an explicit consideration of molecular interactions between two adjacent polymer chains. Good agreement was achieved between the experiment and theory in both spectra. The temperature-sensitive bands at ∼70 cm–1 in FIR and at 125 cm–1 in Raman comprise the out-of-plane C═O bending motion. The temperature-dependent shifts of the low-frequency bands were successfully simulated by the DFT-spectral calculation, exploring that the main origin of the shifts is the thermal expansion...

Endothelial HMEC-1 cells incubated with pro-inflammatory cytokine TNF-α for 6 and 24 hours were studied as a model of inflammation using Raman imaging. Striking changes in distribution, composition and concentration of cellular lipids were observed after exposure to TNF-α compared to the control. In particular, 3D Raman imaging revealed a significant increase in the amount of lipid entities formed under inflammation. Lipid bodies were randomly distributed in the cytoplasm and two types of droplets were assembled: more saturated one, in spectral characteristics resembling phosphatidylcholine and saturated cholesteryl esters, observed also in the control, and highly unsaturated one, containing also cholesterols, being a hallmark of inflamed cells. The statistical analysis showed that the number of lipid bodies was significantly dependent on the exposure time to TNF-α. Overall, observed formation of unsaturated lipid droplets can be directly correlated with the increase in production of prostacyclins - endogenous inflammation mediators.

Cellular differentiation proceeds along complicated pathways, even when it is induced by extracellular signaling molecules. One of the major reasons for this complexity is the highly multidimensional internal dynamics of cells, which sometimes causes apparently stochastic responses in individual cells to extracellular stimuli. Therefore, to understand cell differentiation, it is necessary to monitor the internal dynamics of cells at single-cell resolution. Here, we used a Raman and autofluorescence spectrum analysis of single cells to detect dynamic changes in intracellular molecular components. MCF-7 cells are a human cancer-derived cell line that can be induced to differentiate into mammary-gland-like cells with the addition of heregulin (HRG) to the culture medium. We measured the spectra in the cytoplasm of MCF-7 cells during 12 days of HRG stimulation. The Raman scattering spectrum, which was the major component of the signal, changed with time. A multicomponent analysis of the Raman spectrum revealed that the dynamics of the major components of the intracellular molecules, including proteins and lipids, changed cyclically along the differentiation pathway. The background autofluorescence signals of Raman scattering also provided information about the differentiation process. Using the total information from the Raman and autofluorescence spectra, we were able to visualize the pathway of cell differentiation in the multicomponent phase space.

Step, ridge, and crack submicro/nanostructures of epitaxial graphene on 4H-SiC (0001) were characterized using tip-enhanced Raman scattering (TERS) spectroscopy. The nanostructures were created during graphene synthesis due to a difference in the thermal expansion coefficient of graphene and SiC. These structures are a distinctive property of epitaxial graphene, together with other desirable properties, such as large graphene sheet and minimal defects. The results of this study illustrate that the exceptional spatial resolution of TERS allows spectroscopic measurements of individual nanostructures, a feat which normal Raman spectroscopy is not capable of. By analyzing TERS spectra, the change of local strain on the nanoridge and decreased graphene content in the submicrometer crack were detected. Using G′ band positions in the TERS spectra, the strain difference between the ridge center and flat area was calculated to be 1.6 × 10–3 and 5.8 × 10–4 for uniaxial and biaxial strain, respectively. This confir...