Phonon Anharmonicity and Spin-Phonon Coupling in CrI3.

We report on the far-infrared, temperature-dependent optical properties of a CrI3 transition metal halide single crystal, a van der Waals ferromagnet (FM) with a Curie temperature of 61 K. In addition to the expected phonon modes determined by the crystalline symmetry, the optical reflectance and transmittance spectra of CrI3 single crystals show many other excitations as a function of temperature as a consequence of the combination of a strong lattice anharmonicity and spin-phonon coupling. This complex vibrational spectrum highlights the presence of entangled interactions among the different degrees of freedom in CrI3.

Real-time quantitative detection of styrene in atmosphere in presence of other volatile-organic compounds using a portable device.

Exposure to styrene is a major safety concern in the fibreglass processing industry. This compound is classified by the International Agency for Research on Cancer as a possible human carcinogen. Several types of analytical equipment exist for detecting volatile organic compounds (VOCs) in the atmosphere; however, most of them operate ex-situ or do not provide easy discrimination between different molecules. This work introduces an improved and portable method based on FTIR spectroscopy to analyse toxic gaseous substances in working sites down to a concentration of less than 4 ppm. Styrene and a combination of VOCs typically associated with it in industrial processes, such as acetone, ethanol, xylene and isopropanol, have been used to calibrate and test the methodology. The results demonstrate that the technique offers the possibility to discriminate between different gaseous compounds in the atmosphere with a high degree of confidence and obtain very accurate quantitative information on their concentration, down to the ppm level, even when different VOCs are present in a mixture.

The Puzzling Problem of Cardiolipin Membrane-Cytochrome c Interactions: A Combined Infrared and Fluorescence Study.

The interaction of cytochrome c (cyt c) with natural and synthetic membranes is known to be a complex phenomenon, involving both protein and lipid conformational changes. In this paper, we combined infrared and fluorescence spectroscopy to study the structural transformation occurring to the lipid network of cardiolipin-containing large unilamellar vesicles (LUVs). The data, collected at increasing protein/lipid ratio, demonstrate the existence of a multi-phase process, which is characterized by: (i) the interaction of cyt c with the lipid polar heads; (ii) the lipid anchorage of the protein on the membrane surface; and (iii) a long-distance order/disorder transition of the cardiolipin acyl chains. Such effects have been quantitatively interpreted introducing specific order parameters and discussed in the frame of the models on cyt c activity reported in literature.

Experimental signature of a topological quantum dot.

Topological insulator nanoparticles (TINPs) host topologically protected Dirac surface states, just like their bulk counterparts. For TINPs of radius <100 nm, quantum confinement on the surface results in the discretization of the Dirac cone. This system of discrete energy levels is referred to as a topological quantum dot (TQD) with energy level spacing on the order of Terahertz (THz), which is tunable with material-type and particle size. The presence of these discretized energy levels in turn leads to a new electron-mediated phonon-light coupling in the THz range, and the resulting mode can be observed in the absorption cross-section of the TINPs. We present the first experimental evidence of this new quantum phenomenon in Bi2Te3 topological quantum dots, remarkably observed at room temperature.

Lucio Fontana and the light: Spectroscopic analysis of the artist's collection at the National Gallery of Modern and Contemporary Art.

In this work the results deriving from the characterization of materials used by Lucio Fontana to realize some of his artworks are presented. Specifically, object of analyses are three artworks from the collection of National Gallery of Modern and Contemporary Art in Rome, whose complex composition required the combination of different diagnostic techniques for a complete characterization. Microscopic fragments from the artworks were analyzed through X-Ray Fluorescence (XRF), Fourier Transformed InfraRed (FTIR) spectroscopy, in transmission and in Attenuated Total Reflectance (ATR) mode, and Raman spectroscopy to obtain information on the atomic and molecular species and to individuate pigments and binders. In one case, the richness in different materials and the not homogenous distribution on the artwork surface required the additional use of portable techniques, as Visible Light Reflectance and Raman spectroscopies with optical fiber probes, to map the surface. The combination of these techniques resulted to be a powerful tool in order to obtain a complete characterization of artist's choices and provided new information to understand the evolution of his technique.

Model-based correction algorithm for Fourier Transform infrared microscopy measurements of complex tissue-substrate systems.

Model-based algorithms have recently attracted much attention for data pre-processing in tissue mapping and imaging by Fourier transform infrared micro-spectroscopy (FTIR). Their versatility, robustness and computational performance enabled the improvement of spectral quality by mitigating the impact of scattering and fringing in FTIR spectra of chemically homogeneous biological systems. However, to date, no comprehensive algorithm has been optimized and automated for large-area FTIR imaging of histologically complex tissue samples. Herein, for the first time, we propose a unique, integrated and fully-automated Multiple Linear Regression Multi-Reference (MLR-MR) method for correcting linear baseline effects due to diffuse scattering, for compensating substrate thickness inhomogeneity and accounting for sample chemical heterogeneity in FTIR images. In particular, the algorithm uses multiple-reference spectra for histologically heterogeneous biological samples. The performance of the procedure was demonstrated for FTIR imaging of chemically complex rat brain frontal cortex tissue samples, mounted onto Ultralene® films. The proposed MLR-MR correction algorithm allows the efficient retrieval of "pure" absorbance spectra and greatly improves the histological fidelity of FTIR imaging data, as compared with the one-reference approach. In addition, the MLR-MR algorithm here presented opens up the possibility for extracting information on substrate thickness variability, thus enabling the indirect evaluation of its topography. As a whole, the MLR-MR procedure can be easily extended to more complex systems for which Mie scattering effects must also be eliminated.

Infrared biomarkers of impaired cystic fibrosis transmembrane regulator protein biogenesis.

The mid-infrared (IR) spectra of human cystic fibrosis (CF) cells acquired by Fourier transform infrared microspectroscopy were compared with those of non-CF cells. Within the 1700 to 1480 cm-1 spectral domain of amides, unsupervised explorative principal component analysis identified a few variables reflecting quantitative and qualitative vibrations arising from protein secondary structures and amino acid side chains. Their pattern reflected α-helix to ß-sheet transitions in bronchial epithelial cells and in immortalized peripheral blood mononuclear cells from patients with R1162X missense or in-frame F508del mutations in the cystic fibrosis transmembrane regulator gene (Cftr). Similar transitions have been described in IR spectra of cells, tissues and body fluids of patients affected with some neurodegenerative diseases characterized by the accumulation of misfolded protein aggregates. The variables pattern was able to distinguish CF cells from non-CF cells and was modified by molecular compounds used to rescue the unbalanced folding process of mutated cystic fibrosis transmembrane regulator (CFTR) anion channel. To our knowledge, this is the first experimental evidence of spectroscopic biomarkers of the impaired biogenesis of CFTR by IR microanalysis in the spectra of human CF bronchial epithelial and lymphoblastoid cells.

Leptin induction following irradiation is a conserved feature in mammalian epithelial cells and tissues.

PURPOSE: Leptin (LEP) is a peptide hormone with multiple physiological functions. Besides its systemic actions, it has important peripheral roles such as a mitogen action on keratinocytes following skin lesions. We previously showed that LEP mRNA is significantly induced in response to neutron irradiation in mouse skin and that the protein increases in the irradiated epidermis and in the related subcutaneous adipose tissue. In this work, we investigated the post-transcriptional regulation of LEP by miRNAs and the conservation of LEP's role in radiation response in human cells. METHODS: We used microarray analysis and real-time polymerase chain reaction (RT-PCR) to analyze modulation of miRNAs potentially targeting LEP in mouse skin following irradiation and bioinformatic analysis of transcriptome of irradiated human cell lines and cancer tissues from radiotherapy-treated patients to evaluate LEP expression. RESULTS AND CONCLUSIONS: We show that a network of miRNAs potentially targeting LEP mRNA is modulated in irradiated mouse skin and that LEP itself is significantly modulated by irradiation in human epithelial cell lines and in breast cancer tissues from radiotherapy-treated patients. These results confirm and extend the previous evidence that LEP has a general and important role in the response of mammalian cells to irradiation.

Strong nonlinear terahertz response induced by Dirac surface states in Bi2Se3 topological insulator.

Electrons with a linear energy/momentum dispersion are called massless Dirac electrons and represent the low-energy excitations in exotic materials such as graphene and topological insulators. Dirac electrons are characterized by notable properties such as a high mobility, a tunable density and, in topological insulators, a protection against backscattering through the spin-momentum locking mechanism. All those properties make graphene and topological insulators appealing for plasmonics applications. However, Dirac electrons are expected to present also a strong nonlinear optical behaviour. This should mirror in phenomena such as electromagnetic-induced transparency and harmonic generation. Here we demonstrate that in Bi2Se3 topological insulator, an electromagnetic-induced transparency is achieved under the application of a strong terahertz electric field. This effect, concomitantly determined by harmonic generation and charge-mobility reduction, is exclusively related to the presence of Dirac electron at the surface of Bi2Se3, and opens the road towards tunable terahertz nonlinear optical devices based on topological insulator materials.

Multivariate analysis applied to Raman mapping of dye-functionalized carbon nanotubes: a novel approach to support the rational design of functional nanostructures.

Principal component analysis is applied to analyse the Raman maps collected on carbon nanotubes at different degrees of oxidation and functionalization with dye labeling molecules. The results are used to demonstrate that the technique is extremely effective in clustering data and comparing preparation protocols, so that it enables drawing of a fast and reliable classification of the molecule propensity to interact with pristine and oxidized carbon nanotubes. The spectral findings are supported and elucidated by several experimental techniques, thermogravimetry and steady-state and time-resolved fluorescence measurements, and by computational modeling, showing that the proposed methodology could represent a powerful and routine test for the rational design of functional nanostructures.

Graphitic Patterns on CVD Diamond Plate as Microheating/Thermometer Devices.

A simple compact temperature sensor and microheater in a wide temperature range has been developed, realizing a laser-patterned resistive structure on the surface of a synthetic polycrystalline diamond plate. Imaging and spectroscopy techniques used to investigate morphology, structure, and composition of the pattern showed that it incorporates different nondiamond carbon phases. Transport experiments revealed the semiconducting behavior of this microresistor. Thermal power measurements versus temperature are presented. A possible application of this device that may easily match compact experimental layouts avoiding both thermal anchoring offset and mechanical stress between sample and sensor is discussed. The patterned structure undergoes testing as a microthermometer, providing fast response and excellent stability versus time. It exhibits a good sensitivity that coupled to an easy calibration procedure minimizes errors and guarantees high accuracy. Plot of temperature versus input power of the resistive patterned line used as microheater shows a linear behavior in an extended temperature range.

Degradation process of lead chromate in paintings by Vincent van Gogh studied by means of spectromicroscopic methods. 4. Artificial aging of model samples of co-precipitates of lead chromate and lead sulfate.

Previous investigations about the darkening of chrome yellow pigments revealed that this form of alteration is attributable to a reduction of the original Cr(VI) to Cr(III), and that the presence of sulfur-containing compounds, most often sulfates, plays a key role during this process. We recently demonstrated that different crystal forms of chrome yellow pigments (PbCrO(4) and PbCr(1-x)S(x)O(4)) are present in paintings by Vincent van Gogh. In the present work, we show how both the chemical composition and the crystalline structure of lead chromate-based pigments influence their stability. For this purpose, oil model samples made with in-house synthesized powders of PbCrO(4) and PbCr(1-x)S(x)O(4) were artificially aged and characterized. We observed a profound darkening only for those paint models made with PbCr(1-x)S(x)O(4), rich in SO(4)(2-) (x ≥ 0.4), and orthorhombic phases (>30 wt %). Cr and S K-edge micro X-ray absorption near edge structure investigations revealed in an unequivocal manner the formation of up to about 60% of Cr(III)-species in the outer layer of the most altered samples; conversely, independent of the paint models' chemical composition, no change in the S-oxidation state was observed. Analyses employing UV-visible diffuse reflectance and Fourier transform infrared spectroscopy were performed on unaged and aged model samples in order to obtain additional information on the physicochemical changes induced by the aging treatment.

Functional histology of glioma vasculature by FTIR imaging.

Fourier-transform infrared (FTIR) imaging has been used to investigate brain tumor angiogenesis using a mice solid tumor model and bare-gold (∅ 25 nm) or BaSO(4) (∅ 500 nm) nanoparticles (NP) injected into blood vasculature. FTIR images of 20-µm-thick tissue sections were used for chemical histology of healthy and tumor areas. Distribution of BaSO(4)-NP (using the 1,218-1,159 cm(-1) spectral interval) revealed clearly all details of blood vasculature with morphological abnormalities of tumor capillaries, while Au-NP (using the 1,046-1,002 cm(-1) spectral interval) revealed also diffusion properties of leaky blood vessels. Diffusion of Au-NP out of vascular space reached 64 ± 29 µm, showing the fenestration of "leaky" tumor blood vessels, which should allow small NP (<100 nm, as for Au-NP) to diffuse almost freely, while large NP should not (as for BaSO(4)-NP in this study). Therefore, we propose to develop FTIR imaging as a convenient tool for functional molecular histology imaging of brain tumor vasculature, both for identifying blood capillaries and for determining the extravascular diffusion space offered by vessel fenestration.

Bioimaging of cells and tissues using accelerator-based sources.

A variety of techniques exist that provide chemical information in the form of a spatially resolved image: electron microprobe analysis, nuclear microprobe analysis, synchrotron radiation microprobe analysis, secondary ion mass spectrometry, and confocal fluorescence microscopy. Linear (LINAC) and circular (synchrotrons) particle accelerators have been constructed worldwide to provide to the scientific community unprecedented analytical performances. Now, these facilities match at least one of the three analytical features required for the biological field: (1) a sufficient spatial resolution for single cell (< 1 mum) or tissue (<1 mm) analyses, (2) a temporal resolution to follow molecular dynamics, and (3) a sensitivity in the micromolar to nanomolar range, thus allowing true investigations on biological dynamics. Third-generation synchrotrons now offer the opportunity of bioanalytical measurements at nanometer resolutions with incredible sensitivity. Linear accelerators are more specialized in their physical features but may exceed synchrotron performances. All these techniques have become irreplaceable tools for developing knowledge in biology. This review highlights the pros and cons of the most popular techniques that have been implemented on accelerator-based sources to address analytical issues on biological specimens.