Conventional FTIR Spectroscopy Research Articles

Origins and consequences of asymmetric nano-FTIR interferograms

Infrared scattering-type near-field optical microscopy, IR s-SNOM, and its broadband variant, nano-FTIR, are pioneering, flagship techniques for their ability to provide molecular identification and material optical property information at a spatial resolution well below the far-field diffraction limit, typically less than 25 nm. While s-SNOM and nano-FTIR instrumentation and data analysis have been discussed previously, there is a lack of information regarding experimental parameters for the practitioner, especially in the context of previously developed frameworks. Like conventional FTIR spectroscopy, the critical component of a nano-FTIR instrument is an interferometer. However, unlike FTIR spectroscopy, the resulting interference patterns or interferograms are typically asymmetric. Here, we unambiguously describe the origins of asymmetric interferograms recorded with nano-FTIR instruments, give a detailed analysis of potential artifacts, and recommend optimal instrument settings as well as data analysis parameters.

Complete characterization of RNA biomarker fingerprints using a multi-modal ATR-FTIR and SERS approach for label-free early breast cancer diagnosis.

Breast cancer is a prevalent form of cancer worldwide, and the current standard screening method, mammography, often requires invasive biopsy procedures for further assessment. Recent research has explored microRNAs (miRNAs) in circulating blood as potential biomarkers for early breast cancer diagnosis. In this study, we employed a multi-modal spectroscopy approach, combining attenuated total reflection Fourier transform infrared (ATR-FTIR) and surface-enhanced Raman scattering (SERS) to comprehensively characterize the full-spectrum fingerprints of RNA biomarkers in the blood serum of breast cancer patients. The sensitivity of conventional FTIR and Raman spectroscopy was enhanced by ATR-FTIR and SERS through the utilization of a diamond ATR crystal and silver-coated silicon nanopillars, respectively. Moreover, a wider measurement wavelength range was achieved with the multi-modal approach than with a single spectroscopic method alone. We have shown the results on 91 clinical samples, which comprised 44 malignant and 47 benign cases. Principal component analysis (PCA) was performed on the ATR-FTIR, SERS, and multi-modal data. From the peak analysis, we gained insights into biomolecular absorption and scattering-related features, which aid in the differentiation of malignant and benign samples. Applying 32 machine learning algorithms to the PCA results, we identified key molecular fingerprints and demonstrated that the multi-modal approach outperforms individual techniques, achieving higher average validation accuracy (95.1%), blind test accuracy (91.6%), specificity (94.7%), sensitivity (95.5%), and F-score (94.8%). The support vector machine (SVM) model showed the best area under the curve (AUC) characterization value of 0.9979, indicating excellent performance. These findings highlight the potential of the multi-modal spectroscopy approach as an accurate, reliable, and rapid method for distinguishing between malignant and benign breast tumors in women. Such a label-free approach holds promise for improving early breast cancer diagnosis and patient outcomes.

Mid-IR refractive index sensor for detecting proteins employing an external cavity quantum cascade laser-based Mach-Zehnder interferometer.

Novel laser light sources in the mid-infrared region enable new spectroscopy schemes beyond classical absorption spectroscopy. Herein, we introduce a refractive index sensor based on a Mach-Zehnder interferometer and an external-cavity quantum cascade laser that allows rapid acquisition of high-resolution spectra of liquid-phase samples, sensitive to relative refractive index changes down to 10-7. Dispersion spectra of three model proteins in deuterated solution were recorded at concentrations as low as 0.25 mg mL-1. Comparison with Kramers-Kronig-transformed Fourier transform infrared absorbance spectra revealed high conformance, and obtained figures of merit compare well with conventional high-end FTIR spectroscopy. Finally, we performed partial least squares-based multivariate analysis of a complex ternary protein mixture to showcase the potential of dispersion spectroscopy utilizing the developed sensor to tackle complex analytical problems. The results indicate that laser-based dispersion sensing can be successfully used for qualitative and quantitative analysis of proteins.

Mid-Infrared Spectroscopy Platform Based on GaAs/AlGaAs Thin-Film Waveguides and Quantum Cascade Lasers

The performance and versatility of GaAs/AlGaAs thin-film waveguide technology in combination with quantum cascade lasers for mid-infrared spectroscopy in comparison to conventional FTIR spectroscopy is presented. Infrared radiation is provided by a quantum cascade laser (QCL) spectrometer comprising four tunable QCLs providing a wavelength range of 5-11 μm (1925-885 cm(-1)) within a single collimated beam. Epitaxially grown GaAs slab waveguides serve as optical transducer for tailored evanescent field absorption analysis. A modular waveguide mounting accessory specifically designed for on-chip thin-film GaAs waveguides is presented serving as a flexible analytical platform in lieu of conventional attenuated total reflection (ATR) crystals uniquely facilitating macroscopic handling and alignment of such microscopic waveguide structures in real-world application scenarios.

Corrosion Inhibition of Aluminum by Psidium Guajava Seeds in HCl Solution

The corrosion inhibition and adsorption of ethanol extracts of Psidium guajava seeds (EE Pg S), for aluminum in 0.5 N HCl solutions, were inves tigated using conventional weight loss, FTIR spectroscopy and SEM analysis techniques. The results showed that EE Pg S performed well as inhibitor for the corrosion of aluminum in hydrochloric acid media. FTIR results showed that the inhibition mech anism was by adsorption process, through the functional groups present in the extrac t. Inhibition efficiency increased with increasing concentration of the plant extract, but decreased with the temperature rise. The weight loss data were fitted into a number of i sotherms, though Langmuir model was found to be the best fit. The SEM photographs c onfirmed the protection offered by the extract on the surface of the metal.

Chemical Composition and Surface Properties of Paper Mill Sludge and their Impact on High Density Polyethylene (HDPE) Composites

A comparative study was conducted using paper mill sludge from three different pulping processes at two primary sludge (PS) to secondary sludge (SS) ratios to better understand the role of PS and SS in the development of wood/high-density polyethylene (HDPE) composite properties. Sludge samples from a thermomechanical (TMP), chemico-thermomechanical (CTMP), and Kraft pulping process were used at three proportions (20, 30, and 40%) to produce different composites. Pulp and combined sludge samples were characterized by conventional chemical analysis and FTIR spectroscopy. FTIR spectroscopy enabled the characterization of the inorganic content in the sludge. Results showed that the variation in composite properties according to sludge type could be explained by the chemical composition, regardless of pulping process or SS:PS ratio. Ash and cellulose content were the dominant factors in explaining the composite mechanical properties, and nitrogen content, although low, was the dominant factor in explaining composite toughness.

Studying variations in bone composition at nano-scale resolution: a preliminary report.

Bone has a hierarchical structure extending from the micrometer to the nanometer scale. We report here the first analysis of non-human primate osteonal bone obtained using a spectrometer coupled to an AFM microscope (AFM-IR), with a resolution of 50-100 nm. Average spectra correspond to those observed with conventional FTIR spectroscopy. The following validated FTIR parameters were calculated based on intensities observed in scans covering ~60 µm from the osteon center: mineral content (1030/1660 cm(-1)), crystallinity (1030/1020 cm(-1)), collagen maturity (1660/1690 cm(-1)), and acid phosphate content (1128/1096 cm(-1)). A repeating pattern was found in most of these calculated IR parameters corresponding to the reported inter- and intra-lamellar spacing in human bone, indicating that AFM-IR measurements will be able to provide novel compositional information on the variation in bone at the nanometer level.

Cure Monitoring of Epoxy Resin by Simultaneous DSC/FTIR

The cross-linking kinetics of an epoxy/amine resin system was studied using the conventional DSC and FTIR spectroscopy, respectively. Conventional DSC was modified to accommodate two fibre optic probes which could be used to monitor the spectra of epoxy/amine resin system during cure. The cross-linking kinetics for the epoxy/amine resin system obtained via the conventional DSC and FTIR and simultaneous DSC/FTIR were similar. The feasibility of using a simple bifurcated fibre optic probe to link the DSC to the FTIR spectrometer was demonstrated.

Investigation of blood vessels in glioblastoma at a micrometric scale: a comparative study by synchrotron and conventional micro-FTIR

Glioblastoma, the most malignant brain tumor in humans, is characterized by being severely angiogenic and an increase in vascularization generally worsens the prognosis of patients. Finding the best approach to characterize glioma blood vessels (BVs) is very important in view of helping to determine any specific biomolecular markers of these tumors. In previous work by conventional FTIR spectroscopy we were able to discriminate some molecular markers in order to differentiate between normal and tumor BVs in glioma tissue sections. The aim of the present study was to assess whether FTIR microspectroscopy using a synchrotron radiation (SR) source could provide advantages over a classical globar IR source for detailed spectral analysis on such small features like micro-BVs. Using chemometric analysis such as PCA and HCA, the results show that a high brilliant SR beam provides a very satisfying quality signal compared with the globar source to study spectral images for relevant analysis of glioma big and micro-BVs and determination of subtle molecular markers characterizing them from the surrounding tissue.

An assessment of various powdered baby formulas by conventional methods (DSC) or FT-IR spectroscopy

Milk components are assumed to be uniformly distributed in a concentrate whilst it is being dried. During milk powder production, these components are redistributed in the drying droplets and the powder surface composition is significantly different from that of the bulk of it. The objective of this article was to analyze and compare phase transitions of powdered baby formulas as well as to make a study of their FT-IR spectra. Food powders of different composition were tested by a differential scanning calorimeter (DSC, TA Instruments Q 200) with a normal pressure cell and a System 2000 spectrophotometer. Significant differences were observed in the shape of curves of the mixtures and the agglomerates. The observed phase transitions in powders depended on fat content. Characteristic peaks of melting lactose were observed in the curves of the powdered baby formulas. The IR spectra proved to be useful in determining adulteration of baby formulas. Both methods were complimentary during a thorough evaluation of these food powders.

One- and two-dimensional Fourier transform infrared correlation spectroscopy of Phyllagathis rotundifolia

Abstract 1D- and 2D-IR with thermal perturbation was utilized in this study for the macroscopic fingerprinting of Phyllagathis rotundifolia. Conventional FTIR spectroscopy showed limited spectral differences for the species with a closely related species, Phyllagathis praetermissa. However, the visual 2D-IR spectra were able to enhance IR absorptions and generate characteristic IR fingerprint for P. rotundifolia. This approach combined with PCA is also applicable to detect mixtures of P. rotundifolia and P. praetermissa. By using this non-destructive IR fingerprinting, the identification and quality control of P. rotundifolia can be achieved more effectively.

Investigation of biodeteriorated historical textiles by conventional and synchrotron radiation FTIR spectroscopy

We have examined specimens of historical biodeteriorated cellulose textiles using synchrotron radiation and conventional source FTIR spectroscopy. The main aim of our research was to investigate structural changes caused by ageing and biodeterioration in different types of cellulose fibres. We compared the results, obtained with both methods regarding spectral quality and information obtained with each method. Additionally, we obtained mapping images of the cross sections of the investigated specimens using synchrotron FTIR in order to analyze structural changes in cross sections, caused due to biodeterioration.

Stress-induced proton disorder in hydrous ringwoodite

We have measured in situ high-pressure IR absorption of synthetic hydrous (MgxFe1−x)2SiO4 ringwoodites (x = 0.00 to 0.61) up to a maximum pressure of 30 GPa. In our study, we combined the megabar-type diamond-anvil cell (DAC) with conventional and synchrotron FTIR spectroscopy. The high-pressure measurements were performed in three different pressure-transmitting environments: (1) CsI powder, (2) cryogenically loaded liquid argon, and (3) cryogenically loaded liquid argon annealed at 8.6 GPa at temperature of 120°C before further pressure increase. Between 10 and 12 GPa, all the samples loaded with methods (1) and (2), independent on composition, showed a sudden disappearance of the prominent OH-stretching feature and simultaneous discontinuities and/or changes in the pressure dependence of lattice vibrations compared with spectra of samples loaded with method (3). In experiments performed with method (3) the OH-stretching vibrations as well as lattice vibrations could be observed up to 30 GPa and their pressure behavior (dν/dP) can well be described by linear fits. Molecular vibrations, such as the OH stretching, are sensitive to non-hydrostatic conditions, especially in minerals with highly symmetric structures. We interpret the disappearance of the OH bands using methods (1) and (2) as a stress-induced proton disordering in hydrous ringwoodite. Our results confirm that argon pressure medium produces strongly non-hydrostatic conditions comparable to CsI or KBr, if it is not thermally annealed at pressures above 8 GPa. Our results suggest that the transition observed in hydrous Mg-ringwoodite end member is not present in compositions containing Fe. By comparing the behavior of samples compressed in different environments, we suggest that sudden disappearance of the OH-stretching band in hydrous ringwoodite could be driven by deterioration of the quasi-hydrostatic stress condition instead of a pressure-induced effect.

Detection of Hybridization on Nanografted Oligonucleotides Using Scanning Near-Field Infrared Microscopy

We demonstrate that scattering scanning near-field infrared microscopy (s-SNIM) is a label free analytical method allowing hybridization detection of nanografted DNA patches on a sub-μM scale. On the basis of their distinct dielectric properties in the IR, we can distinguish between single stranded and double stranded DNA. The sensitivity of s-SNIM is found to be increased by 7 orders of magnitude compared to conventional FTIR spectroscopy due to the tip enhanced interaction with the substrate.

Compositional homeostasis of the dinoflagellate Protoceratium reticulatum grown at three different pCO 2

In the CO 2-richer world that awaits us, the impact of elevated pCO 2 on the allocation of resources in phytoplankton may have profound repercussions on the physiology of the microalgae and on the ecology of the ecosystems of which they are part. We studied the overall physiology and cell composition of the potentially toxic dinoflagellate Protoceratium reticulatum subjected to a medium-term increase of CO 2. The physiological responses investigated were growth rates, cell size, photosynthetic and respiratory rates, and key enzyme activities. Cell composition was assessed by conventional analytical methods and FTIR spectroscopy. After 3 generations of incubation at current atmospheric, high and very high pCO 2 (380, 1000, 5000 ppm CO 2), growth, photosynthesis, and dark respiration rates increased significantly, but the internal composition was only slightly affected. We propose the homeostasis of cell composition as a strategy that organisms can use to tackle environmental perturbations, especially when they are of relatively short duration.

Time-Resolved Dynamics of the OH Stretching Vibration in Aqueous NaCl Hydrate

We report on the first time-resolved study of the OH stretching vibration in NaCl dihydrate with the use of two-color IR spectroscopy. The sample is characterized by conventional FTIR spectroscopy. The water molecules bound in the hydrate show two well separated absorption bands at 3426 cm(-1) and 3541 cm(-1). The transient data display an ultrafast heating of the polycrystalline ice-hydrate samples after excitation of the OH stretching vibration and its transient relaxation. The relaxation time of the low-frequency OH stretching band in the NaCl hydrate is measured to be 6.8 +/- 1 ps. The dynamics are significantly slower than those measured in neat water. This fact, together with the reproducible crystalline environment reveals the potential of aqueous hydrates for a systematic investigation of the OH stretching vibration in varying hydrogen bonding environments.

Identification of actinide molecule complexes: A new vibrational spectroscopic approach at the free-electron laser facility FELBE

Photothermal beam deflection (PTBD) spectroscopy using a free-electron laser (FEL) as a coherent pulsed pump source was applied for recording infrared spectra of actinide molecule complexes. We demonstrate that reliable spectra of samples containing uranyl and neptunyl compounds can be obtained in the mid-infrared region which was verified by conventional FT-IR spectroscopy. Since photothermal techniques are generally capable of detecting very low absorptions we tried to evaluate the minimum content of actinide ions which can still be detected by our setup of the PTBD experiment. It was found that the limit is obviously given by the background absorption of the hygroscopic KBr matrix of the samples which is originated by residual water. Furthermore, we present an overview about the technical equipment of the FEL-laboratory which is suitable for spectroscopic investigations in actinide research.

Examination of Interactions of Oppositely Charged Proteins in Gels

Understanding the interactions of proteins with one another serves as an important step for developing faster protein separation methods. To examine protein-protein interactions of oppositely charged proteins, fluorescently labeled albumin and poly-l-lysine were subjected to electrophoresis in agarose gels, in which the cationic albumin and the anionic poly-L-lysine were allowed to migrate toward each other and interact. Fluorescence microscopy was used to image fluorescently tagged proteins in the gel. The secondary structure of the proteins in solution was studied using conventional FTIR spectroscopy. Results showed that sharp interfaces were formed where FITC tagged albumin met poly-L-lysine and that the interfaces did not migrate after they had been formed. The position of the interface in the gel was found to be linearly dependent upon the relative concentration of the proteins. The formation of the interface also depended upon the fluorescent tag attached to the protein. The size of the aggregates at the interface, the fluorescence intensity modifications, and the mobility of the interface for different pore sizes of the gel were investigated. It was observed that the interface was made up of aggregates of about 1 microm in size. Using dynamic light scattering, it was observed that the size of the aggregates that formed due to interactions of oppositely charged proteins depended upon the fluorescent tags attached to the proteins. The addition of small amounts of poly-L-lysine to solutions containing FITC albumin decreased the zeta potential drastically. For this, we propose a model suggesting that adding small amounts of poly-L-lysine to solutions containing FITC -albumin favors the formation of macromolecular complexes having FITC albumin molecules on its surface. Although oppositely charged FITC tagged poly-L-lysine and FITC tagged albumin influence each other's migration velocities by forming aggregates, there were no observable secondary structural modifications when the proteins were mixed in solution.

Synchrotron radiation FT-IR micro-spectroscopy of fluorophlogopite in the O–H stretching region

Synchrotron radiation FT-IR polarized micro-spectroscopy has been used to investigate the natural mica fluorophlogopite in order to characterize the stretching vibrations of the OH groups and their orientation relative to the mica cleavage (0 0 1) plane. A procedure to eliminate undesired interference fringes, typically observed when working with thin single-crystals, was set up using an ad hoc sample preparation, and tested. The naturally high brilliance and high polarization properties of synchrotron radiation allows to study very small flakes and hence offers new analytical possibilities in comparison to conventional powder FT-IR spectroscopy.

Synchrotron radiation FTIR micro-spectroscopy of natural layer-silicates in the O–H stretching region

Synchrotron radiation FTIR polarized micro-spectroscopy has been used to investigate natural mica crystals in order to characterize the stretching vibrations of the OH groups and their orientation relative to the mica cleavage (0 0 1) plane. A procedure to eliminate undesired interference fringes, typically observed when working with thin single-crystals, was set up using an ad hoc sample preparation, and tested. The naturally high brilliance and high polarization properties of synchrotron radiation allows to study very small flakes and hence offers new analytical possibilities in comparison to conventional powder FTIR spectroscopy.