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Femtosecond transient absorption (fs-TA) and Ultrafast Raman Loss Spectroscopy (URLS) have been applied to reveal the excited state dynamics of bis(phenylethynyl)benzene (BPEB), a model system for one-dimensional molecular wires that have numerous applications in opto-electronics. It is known from the literature that in the ground state BPEB has a low torsional barrier, resulting in a mixed population of rotamers in solution at room temperature. For the excited state this torsional barrier had been calculated to be much higher. Our femtosecond TA measurements show a multiexponential behaviour, related to the complex structural dynamics in the excited electronic state. Time-resolved, excited state URLS studies in different solvents reveal mode-dependent kinetics and picosecond vibrational relaxation dynamics of high frequency vibrations. After excitation, a gradual increase in intensity is observed for all Raman bands, which reflects the structural reorganization of Franck-Condon excited, non-planar rotamers to a planar conformation. It is argued that this excited state planarization is also responsible for its high fluorescence quantum yield. The time dependent peak positions of high frequency vibrations provide additional information: a rapid, sub-picosecond decrease in peak frequency, followed by a slower increase, indicates the extent of conjugation during different phases of excited state relaxation. The CC triple (-C≡C-) bond responds somewhat faster to structural reorganization than the CC double (>C=C<) bonds. This study deepens our understanding of the excited state of BPEB and analogous linear pi-conjugated systems and may thus contribute to the advancement of polymeric "molecular wires." [ABSTRACT FROM AUTHOR]

Self‐heating in organic electronics can lead to anomalous electrical performance and even accelerated degradation. However, in the case of disordered organic semiconductors, self‐heating effects are difficult to quantify using electrical techniques alone due to complex transport properties. Therefore, more direct methods are needed to monitor the impact of self‐heating on device performance. Here, self‐heating in poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta [2,1‐b;3,4‐b′] dithiophene)‐alt‐4,7(2,1,3‐benzothiadiazole)] (PCPDTBT) diodes is visualized using Raman spectroscopy, and thermal effects due to self‐heating are quantified by exploiting temperature‐dependent shifts in the polymer vibrational modes. The temperature increases due to self‐heating are quantified by correlating the Raman shifts observed in electrically biased diodes with temperature‐dependent Raman measurements. Temperature elevations up to 75 K are demonstrated in the PCPDTBT diodes at moderate power of about 2.6–3.3 W cm−2. Numerical modeling rationalizes the significant role of Joule and recombination heating on the diode current–voltage characteristics. This work demonstrates a facile approach for in situ monitoring of self‐heating in organic semiconductors for a range of applications, from fundamental transport studies to thermal management in devices. [ABSTRACT FROM AUTHOR]

Alzheimer’s disease (AD) is a neurodegenerative disease, characterized by the presence of extracellular deposits (plaques) of amyloid-beta peptide and intracellular aggregates of phosphorylated tau. In general, these hallmarks are studied by techniques requiring chemical pre-treatment and indirect labeling. Imaging techniques that require no labeling and could be performed on tissue in its native form could contribute to a better understanding of the disease. In this article a combination of label-free and non-invasive techniques is presented to study the biomolecular composition of AD human brain tissue. We build on previous research that already revealed the autofluorescence property of plaque, and the presence of carotenoids in cored plaques. Here, we present further results on cored plaques: showing blue and green autofluorescence emission coming from the same plaque location. Raman microscopy was used to confirm the presence of carotenoids in the plaque areas, with clear peaks around 1150 and 1514 cmâˆ'1. Carotenoid reference spectra were recorded in hexane solution, but also adsorbed on aggregated A β 42 peptides; the latter agreed better with the Raman spectra observed in plaques. From the six single carotenoids measured, lycopene matched closest with the peak positions observed in the cored plaques. Lastly, stimulated Raman scattering (SRS) microscopy measurements were performed, targeting the shift of the beta-sheet Amide I peak observed in plaques. Employing SRS in the Câ€"H stretch region we also looked for the presence of a lipid halo around plaque, as reported in the literature for transgenic AD mice, but such a halo was not observed in these human AD brain samples. [ABSTRACT FROM AUTHOR]

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Breast cancer is the most prevalent cause of cancer-associated death in women the world over, but if detected early it can be treated successfully. Therefore, it is important to diagnose this disease at an early stage and to understand the biochemical changes associated with cellular transformation and cancer progression. Deregulated lipid metabolism has been shown to contribute to cell transformation as well as cancer progression. In this study, we monitored the biomolecular changes associated with the transformation of a normal cell into an invasive cell associated with breast cancer using Raman microspectroscopy. We have utilized primary normal breast cells, and immortalized, transformed, non-invasive, and invasive breast cancer cells. The Raman spectra were acquired from all these cell lines under physiological conditions. The higher wavenumber (2800-3000 cm-1) and lower wavenumber (700-1800 cm-1) range of the Raman spectrum were analyzed and we observed increased lipid levels for invasive cells. The Raman spectral data were analyzed by principal component-linear discriminant analysis (PC-LDA), which resulted in the formation of distinct clusters for different cell types with a high degree of sensitivity. The subsequent testing of the PC-LDA analysis via the leave-one-out cross validation approach (LOOCV) yielded relatively high identification sensitivity. Additionally, the Raman spectroscopic results were confirmed through fluorescence staining tests with BODIPY and Nile Red biochemical assays. Furthermore, Raman maps from the above mentioned cells under fixed conditions were also acquired to visualize the distribution of biomolecules throughout the cell. The present study shows the suitability of Raman spectroscopy as a non-invasive, label-free, microspectroscopic technique, having the potential of probing changes in the biomolecular composition of living cells as well as fixed cells. [ABSTRACT FROM AUTHOR]

Biomolecular structure elucidation is one of the major techniques for studying the basic processes of life. These processes get modulated, hindered or altered due to various causes like diseases, which is why biomolecular analysis and imaging play an important role in diagnosis, treatment prognosis and monitoring. Vibrational spectroscopy (IR and Raman), which is a molecular bond specific technique, can assist the researcher in chemical structure interpretation. Based on the combination with microscopy, vibrational microspectroscopy is currently emerging as an important tool for biomedical research, with a spatial resolution at the cellular and sub-cellular level. These techniques offer various advantages, enabling label-free, biomolecular fingerprinting in the native state. However, the complexity involved in deciphering the required information from a spectrum hampered their entry into the clinic. Today with the advent of automated algorithms, vibrational microspectroscopy excels in the field of spectropathology. However, researchers should be aware of how quantification based on absolute band intensities may be affected by instrumental parameters, sample thickness, water content, substrate backgrounds and other possible artefacts. In this review these practical issues and their effects on the quantification of biomolecules will be discussed in detail. In many cases ratiometric analysis can help to circumvent these problems and enable the quantitative study of biological samples, including ratiometric imaging in 1D, 2D and 3D. We provide an extensive overview from the recent scientific literature on IR and Raman band ratios used for studying biological systems and for disease diagnosis and treatment prognosis. [ABSTRACT FROM AUTHOR]

Carotenoids are among the key biomarkers in the search for life on other planets, and non-destructive Raman spectroscopy on future rover missions is a potential sensitive detection method, especially under resonant conditions. In this research, reflectance spectra of minerals and microorganisms were measured using ultraviolet/visible diffuse reflectance spectroscopy in order to evaluate potential resonance Raman conditions and the possible degree of sample damage during laser irradiation. We report a photodegradation and semi-quantitative Raman study of β-carotene and the carotenoid-containing extremophile Deinococcus radiodurans mixed with calcite at excitation wavelengths of 440 nm, 532 nm and 785 nm. A different type of carotenoid was detected in a culture of Chroococcidiopsis. Carotenoids embedded in bacterial membranes were found to be less sensitive to photodegradation than in a mineral matrix. Corrections for self-absorption effects were performed using the 1085 cm−1 peak of calcite as an internal standard. Carotenoid-type signals from 1 mg g−1 D. radiodurans in calcite could be detected, corresponding to about 5 µg g−1 β-carotene in calcite (≈0.5% cell weight). This research emphasizes the potential suitability of Raman spectroscopy in the detection of organic biomarkers in future planetary exploration. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In conventional Raman spectroscopic measurements of liquids or surfaces the preferred geometry for detection of the Raman signal is the backscattering (or reflection) mode. For non-transparent layered materials, sub-surface Raman signals have been retrieved using spatially offset Raman spectroscopy (SORS), usually with light collection in the same plane as the point of excitation. However, as a result of multiple scattering in a turbid medium, Raman photons will be emitted in all directions. In this study, Monte Carlo simulations for a three-dimensional layered sample with finite geometry have been performed to confirm the detectability of Raman signals at all angles and at all sides of the object. We considered a non-transparent cuboid container (high density polyethylene) with explosive material (ammonium nitrate) inside. The simulation results were validated with experimental Raman intensities. Monte Carlo simulation results reveal that the ratio of sub-surface to surface signals improves at geometries other than backscattering. In addition, we demonstrate through simulations the effects of the absorption and scattering coefficients of the layers, and that of the diameter of the excitation beam. The advantage of collecting light from all possible 4π angles, over other collection modes, is that this technique is not geometry specific and molecular identification of layers underneath non-transparent surfaces can be obtained with minimal interference from the surface layer. To what extent all sides of the object will contribute to the total signal will depend on the absorption and scattering coefficients and the physical dimensions. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Time-resolved and spatially offset Raman spectroscopies have previously been demonstrated for depth analysis through strongly scattering, non-transparent materials. In this study, several series of tissue phantoms were created with varied compositions and thicknesses to compare the potential of these different Raman techniques for biomedical applications. Polydimethylsiloxane (PDMS) phantoms were made with TiO2 particles suspended as a scattering agent, mimicking the scattering properties of biological tissues. The phantom layers contained embedded biomineral simulating inclusions (sphere or layer-shaped) with varied carbonate to phosphate ratios. The tissue phantoms were studied using Time Resolved Raman Spectroscopy (TRRS), Spatially Offset Raman Spectroscopy (SORS), and their combination, using a single instrumental setup with picosecond pulsed excitation at 720 nm and two different detectors. A comparison is made of the efficiency of these techniques to resolve chemical information from these heterogeneous scattering phantom samples. Measurements with continuous wave detection were found to offer a better signal-to-noise ratio than with TRRS, and in SORS measurements ratios of target to matrix signal were found to vary depending on the structural geometry and optical properties of the phantoms. Anomalous SORS behaviour, in which the relative contribution from the target decreases with offset, was observed in cases where the target was highly scattering and the top layer was relatively transparent. Time gating with an intensified charge-coupled device (ICCD) detector can yield more direct information on the depth of the hidden material. [ABSTRACT FROM AUTHOR]

Time resolved Raman spectroscopy (TRRS) can provide subsurface information from multi-layered samples of transparent and translucent evaporative and silicate minerals up to several centimetres thick. Depth information was obtained using 3-ps pulsed laser excitation at 720 nm and a gated intensified charge-coupled device detector with stepwise increasing delay times. Blocks of different minerals were used as first, second or third layers, and Raman spectra from deeper layers could be detected through 10 mm of translucent calcite and up to 40 mm of transparent halite crystals. Measurements by conventional confocal Raman, as well as spatially offset Raman spectroscopy were also successful in distinguishing different mineral layers. This study establishes the great potential for the use of Raman spectroscopy in future planetary exploration, where TRRS could be used as a non-invasive tool for profiling the (sub-)surface at millimetre-depth resolution. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Ultraviolet resonance Raman spectroscopy is carried out using a continuous wave frequency-doubled argon ion laser operated at 229, 244, and 257 nm in order to characterize the overtones and combination bands for several classes of organic compounds in liquid solutions. Contrary to what is generally anticipated, for molecules such as pyrene and anthracene, strong overtones and combination bands can show up; it is demonstrated that their intensity depends critically on the applied laser wavelength, lithe excitation wavelength corresponds with a purely electronic transition—this applies to a good approximation for 244-nm excitation in the case of pyrene and for 257-nm excitation in the case of anthracene—mostly fundamental vibrations (up to 1700 cm-1) are observed. Overtones and combination bands are detected but are rather weak. However, if the laser overlaps with the vibronic region—as holds for 229- and 257-nm excitation for pyrene and 244-nm excitation for anthracene—very strong bands are found in the region 1700-3400 cm-1. As illustrated for pyrene at 257 nm, all these bands can be assigned to first overtones or binary combinations of fundamental vibrations. Their intensity distribution can roughly be simulated by multiplying the relative intensities of the fundamental bands. Significant bands can also be found in the region 3400-5000 cm-1, corresponding with second overtones and ternary combinations. It is shown that these findings are not restricted to planar and rigid molecules with high symmetry. Substituted pyrenes exhibit similar effects, and relatively strong overtones are also observed for adenosine monophosphate and for abietic acid. The reasons for these observations are discussed, as well as the potential applicability for analytical purposes. [ABSTRACT FROM AUTHOR]

The influence of aqueous electrolytes on the water bending vibration was studied with Raman spectroscopy. For all salts investigated (NaI, NaBr, NaCl, and NaSCN), we observed a nonlinear intensity increase of the water bending vibration with increasing concentration. Different lasers and a tunable frequency-doubled optical parametric oscillator system were used to achieve excitation wavelengths between 785 and 374 nm. Focusing on NaI solutions, the relative enhancement of the water bending vibration was found to increase strongly with excitation photon energy, in line with a preresonance effect from the iodide-water charge-transfer transition. We used multivariate curve resolution (MCR) to decompose the measured Raman spectra of NaI solutions into three interconverting spectral components assigned to bulk water and water molecules interacting with one (X···H-O-H···O) and two (X···H-O-H···X) iodide ions (X = I-). The Raman spectrum of solid sodium iodide dihydrate supports the assignment of the latter. Using the MCR results, relative Raman scattering cross sections of 4.0 ± 0.6 and 14.0 ± 0.1 were calculated for the mono- and di-iodide species, respectively (compared to that of bulk water set to unity). In addition, it was found that at relatively low concentrations each iodide ion affects the Raman spectrum of roughly 22 surrounding water molecules, indicating that the influence of iodide extends beyond the first solvation shell. Our results demonstrate that the Raman bending vibration of water is a sensitive probe, providing new insights into anion solvation in aqueous environments. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is a well-established method for chemical identification, with a wide variety of applications. The two major limitations are that fluorescence can hamper detection, and that Raman imaging is slow; it typically takes multiple hours to measure even a small surface area. We have developed a multimodal setup that mitigates these limitations. The setup has a point-scanning mode that allows for time-gated as well as continuous Raman spectroscopy, and both modes use an 80 MHz, 532 nm excitation laser with up to 20 W of power. The fluorescence suppression capabilities of the setup were demonstrated by comparing time-gated to continuous detection of a Dracaena leaf. Raman bands showed a 4-8 times improvement in signal-to-background ratio, and one band that was invisible in the continuous measurement, became visible in the time-gated measurement. The setup also has a 4-band simultaneously detected wide-field mode. Using a set of beam splitters, the Raman signal from the sample is split. This signal is imaged onto four separate cameras, each with a specific band-pass filter. The wide-field data were processed using principal component analysis with k-means clustering. To illustrate the wide-field capabilities of the setup, a 1 mm 2 sample containing aspirin, caffeine and paracetamol was measured using 10 W excitation power. A 10-second measurement enabled identification of the compounds, and a 1-second measurement showed promising results. This brings the setup close to real-time imaging, showing great potential for applications in quality control or for measuring samples that change over time. [Display omitted] • Wide-field Raman can image 1 mm2 (1 megapixel) with a 10 s acquisition time. • Denoised wide-field Raman shows promising results with a 1 s acquisition time. • Time-gated Raman can be used suppress fluorescence. • The combined setup was tested on pharmaceuticals and plant leaves. [ABSTRACT FROM AUTHOR]

Capillary electrophoresis (CE) and resonance Raman spectroscopy (RRS) with excitation in the deep ultraviolet (UV) region (λ[SUBex]: 244 or 257 nm) were coupled on-line. The potential of this hyphenated technique, denoted as CE-UV-RRS, for analyte confirmation/identification purposes was explored with aromatic sulfonic acids and nucleotides as test compounds. Good-quality UV-RRS spectra could be recorded on-the-fly. Identification limits for the nucleotides were in the 10-125 μg/mL range. The RRS spectra showed sufficient characteristic features to enable analyte confirmation. In addition, the identification power of UV-RRS was studied with substituted pyrenes as model compounds. The compounds were distinguishable on the basis of their RRS spectra at 244 nm. [ABSTRACT FROM AUTHOR]

Investigates the use of ultraviolet resonance Raman spectroscopy as an identification tool for column liquid chromatography. On-line coupling; Use of argon laser for the excitation; Resonance Raman spectra of fluorene, phenanthrene, fluoranthene and pyrene.

Raman spectroscopy can provide highly specific chemical fingerprints of inorganic and organic materials and is therefore expected to play a significant role in interplanetary missions, especially for the search for life elsewhere in our solar system. A major challenge will be the unambiguous detection of low levels of biomarkers on a mineral background. In addition, these biomarkers may not be present at the surface but rather inside or underneath minerals. Strong scattering may prevent focusing deeper into the sample. In this paper, we report the detection of carotenoid-containing microorganisms behind mineral layers using time-resolved Raman spectroscopy (TRRS). Two extremophiles, the bacterium Deinococcus radiodurans and the cyanobacterium Chroococcidiopsis, were detected through translucent and transparent minerals using 440 nm excitation under resonance conditions to selectively enhance the detection of carotenoids. Using 3 ps laser pulses and a 250 ps gated intensified CCD camera provided depth selectivity for the subsurface microorganisms over the mineral surface layer and in addition lowered the contribution of the fluorescent background. Raman spectra of both organisms could be detected through 5 mm of translucent calcite or 20 mm of transparent halite. Multilayered mineral samples were used to further test the applied method. A separate tunable laser setup for resonance Raman and a commercial confocal Raman microscope, both with continuous (non-gated) detection, were used for comparison. This study demonstrates the capabilities of TRRS for the depth-selective analysis through scattering samples, which could be used in future planetary exploration to detect microorganisms or biomarkers within or behind minerals. Key Words: Time-resolved Raman spectroscopy-Resonance Raman- Deinococcus radiodurans- Chroococcidiopsis-Extremophiles-Mineral inclusions. Astrobiology 15, 697-707. [ABSTRACT FROM AUTHOR]

Raman spectroscopy and X-ray fluorescence (XRF) spectroscopy are often used as complementary techniques that are well suited for the analysis of art objects because both techniques are fast, sensitive, and noninvasive and measurements can take place in situ. In most of these studies, both techniques are used separately, in the sense that the spectra are evaluated independently and single conclusions are obtained, considering both results. This paper presents a data fusion procedure for Raman and XRF data for the characterization of pigments used in porcelain cards. For the classification of the analyzed points of the porcelain cards principal component analysis (PCA) was used. A first attempt was made to develop a new procedure for the identification of the pigments using a database containing the fused Raman–XRF data of 24 reference pigments. The results show that the classification based on the fused Raman–XRF data is significantly better than the classifications based on the Raman data or the XRF data separately. [ABSTRACT FROM AUTHOR]

In column liquid chromatography (LC) coupled to conventional Raman spectroscopy (RS) removal of the spectral background of the eluent is often demanding, because of the strong signals of the organic modifier. A new chemometrical method is proposed, called the eluent background subtraction (EBS) method, which can correct for small shape and intensity differences of the eluent spectra. The variations in the eluent spectra are modelled using principal component analysis (PCA). The PCA loading vectors are subsequently used for eluent background correction of the elution spectra of the analyte. The loading vectors are fitted under these spectra by an asymmetric least-squares method. This method was successfully applied under various experimental conditions and performed much better than conventional background correction methods. Analyte detectability was improved by (weighted) averaging of all elution spectra and smoothing via a p-spline function. [Copyright &y& Elsevier]

In this preliminary study, we evaluated four different types of substrate for the at-line coupling of capillary electrophoresis and surface-enhanced (resonance) Raman spectroscopy, CE–SER(R)S, with emphasis on spectral repeatability. We tested Sub1: etched silver foil, Sub2: a vapour-deposited silver film, Sub3: a silver oxalate-precoated silica TLC plate and Sub4: a silica TLC plate on which colloid and poly(l-lysine) were manually added to the analyte spots, used earlier in at-line CE–SE(R)RS. All substrates were first tested by manual spotting using trans-1,2-bis(4-pyridyl)ethylene (BPE) as a model compound for SERS and crystal violet (CV) as a model compound for SE(R)RS. The spectral features of the SE(R)RS spectra of BPE and CV showed a most satisfactory repeatability on all substrates. As expected, the signal intensities varied considerably between runs; this implies that quantification in at-line CE–SE(R)RS should rather be done by means of an on-line absorbance detector. In addition, the suitability of Sub1, Sub2 and Sub4 as deposition substrates after CE was explored using two cationic dyes: CV and basic fuchsin (BF). Good-quality SERRS spectra could be recorded on all three substrates. Although Sub1 and Sub2 have a poor water-sorptivity, they were found to be good substrates for at-line CE–SERRS. They do not require any post-deposition addition of silver colloid and could therefore become attractive alternatives for Sub4. [Copyright &y& Elsevier]

Review: 123 refs. [ABSTRACT FROM AUTHOR]