Fourier transform infrared spectroscopy (FTIR) application chemical characterization of enamel,dentin and bone

Fourier transform infrared spectroscopy (FTIR) has been used extensively for chemical characterization of mineralized tissues in the past few decades. FTIR is an ideal technique to analyze chemical structural properties of natural materials, since the frequencies of several vibrational modes of organic and inorganic molecules are active in the infrared. This review discusses the use of FTIR methodology, highlighting the attenuated total reflection (ATR) sampling mode, particularly for characterization of enamel, dentin and bone tissues. Enamel, dentin and bone, are composed of an organic and a mineral phase. The mineral phase is characterized essentially as nonstoichiometric substituted apatite, being the carbonate and phosphate spectral peaks the main representative of these phase. Organic matrix of the post-eruptive enamel is small (～1% weight (wt)). The dentin and bone organic phases are mainly composed of type I collagen that appears as spectral bands of amide I, amide II, amide III bands. Furthermore, synthetic apatite materials are being designed for total or partial replacement, restoration or augmentation of these biological tissues with FTIR assistance.     

Molecular structural analysis of noncarious cervical sclerotic dentin using Raman spectroscopy

Molecular structure of the sclerotic dentin in noncarious cervical lesions (NCCLs) including both the inorganic phase and organic phase was investigated using Raman spectroscopy. It was found that NCCL sclerotic dentin was hypermineralized with the mineral/matrix ratios 2–3 times higher than those of normal dentin, which was caused by both the increase of mineral content and decrease of organic matrix (collagen) content in the sclerotic dentin. For the inorganic phase, the phosphate band (PO₄³⁻, ν₁, symmetric stretching vibrational mode) in NCCL sclerotic dentin was shifted from 960 to 963 cm⁻¹, and the width of this band was decreased from 16.4 to 10.4 cm⁻¹, indicating that the degree of mineral crystallinity in NCCL sclerotic dentin was higher than that of normal dentin. In addition, the carbonate content in the mineral of NCCL sclerotic dentin was less than that of normal dentin. As compared to the inorganic phase, the changes within the organic phase were not dramatic. However, the changes in collagen cross‐link density along with other spectral changes were still detectable. There was a noteworthy reduction in the ratio of nonreducible to reducible cross‐links in the NCCL sclerotic dentin, indicating that cross‐link breaks occurred in the collagen matrix of the lesions. Copyright © 2009 John Wiley & Sons, Ltd.     

A Raman spectroscopic study of teeth affected with molar–incisor hypomineralisation

Raman spectroscopy was used to chemically map lesions associated with molar–incisor hypomineralisation in human teeth. Three teeth with hypomineralised lesions of differing severity, described as white, yellow or brown, were mapped using integral ratios of major component bands (hydroxyapatite, amide I and b‐type carbonate) and principal component analysis scores values. These lesions were found to contain depleted levels of mineral (hydroxyapatite) compared with those of healthy enamel. Principal component analysis also highlighted changes in the phosphate structure and variations in various organic constituents. These variations were consistent with increased disorder in the mineral component of the hypomineralised tooth lesions. Scanning electron microscopy–energy dispersive X‐ray spectroscopy supported the findings based on Raman spectroscopy. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural and Spectroscopic Investigation of Biomimetic Composites—Promising Agents for the Remineralization of Native Dental Tissue

Biomimetic materials (biocomposites) with an organic-mineral composition related to natural dental tissues (enamel and dentin) are obtained for the first time and their structural and optical characteristics are studied. It is demonstrated by a complex of structural and spectroscopic methods that in the formation of biocomposites, the introduced organic component, bearing a number of amino acids, does not affect the structure of the inorganic component (carbonate-substituted calcium hydroxyapatite) of the sample. The carbonate-substituted calcium hydroxyapatite synthesized using a biogenic source of calcium, which forms the basis of the biocomposite, has a luminescence spectrum similar to that of apatite tooth enamel. The spectrum of the intact dentin of a human tooth has a broader luminescence band than that for the enamel spectrum. It is determined that both organic and inorganic components contribute to the dentin luminescence band. The features found in the luminescence spectra of intact tissues and in simulating biocomposites can be used to develop a procedure for effective early diagnosis of the demineralization of hard dental tissues and general dental examination.     

Functional mapping of carious enamel in human teeth with Raman microspectroscopy

We employed Raman microspectroscopy to measure the Raman spectra of phosphate in sound and carious tooth substance. The peak intensity at 960 cm⁻¹ of the phosphate (PO₄³⁻) symmetric stretching vibrational mode (υ₁) in sound enamel was stronger than that of sound dentin, which indicated that sound enamel contained more phosphate than sound dentin. Furthermore, the element analysis of phosphate in sound teeth substance, measured using a scanning electron microscope (SEM) equipped with an energy dispersive X‐ray spectroscope (EDX), gave similar results to those of the Raman measurement. In addition, the border between sound enamel and dentin was clearly demonstrated by mapping the image of the Raman spectrum of phosphate. The mapping image of phosphate in the carious enamel region revealed a heterogeneous low Raman spectrum intensity of phosphate in the area surrounding carious enamel; this finding indicates that phosphate had dissolved from the tooth substance in such areas. In contrast with the decrease in the Raman spectrum intensity of phosphate, the intensity of amide I increased mainly in the low‐phosphate area. Although it remains very difficult to clinically identify the accurate border between sound and carious tooth substance, this distinction may be enabled by using the Raman spectrum of carious tooth substance. Copyright © 2008 John Wiley & Sons, Ltd.     

Rapid outdoor non‐destructive detection of organic minerals using a portable Raman spectrometer

Raman spectral signatures have been obtained for a series of organic minerals using a compact portable Raman instrument equipped with 785‐nm laser excitation. Well‐resolved Raman spectra of crystalline salts of carboxylic acids, whewellite and mellite, as well as of the aromatic mineral idrialite were recorded. For comparative purposes, an amorphous fossil resin, baltic amber, was also investigated. The results obtained confirm that portable Raman instruments can be considered as excellent tools for field geological applications, including the detection of organic minerals in the frame of outcrops of sedimentary rocks or coal beds. Organic minerals can be added to the list of established biomarkers, including porphyrins, hydrocarbons and organic acids, which are important for the study with regard to future exobiological missions such as the ESA ExoMars mission to detect the presence of extinct or extant life on Mars. Copyright © 2009 John Wiley & Sons, Ltd.     

Investigation of adhesive–dentin interfaces using Raman microspectroscopy and small angle X‐ray scattering

Human dentin specimens were treated with two different etch‐and‐rinse adhesives, Single Bond 2 (SB2) and Prime & Bond NT (PBNT), and two composite resins, TPH and P60. Cross‐sectional samples, approximately 1 mm thick, were analyzed with Raman line mapping and imaging across the dentin–adhesive–composite interface. The integrated intensities of selected bands associated with adhesive, organic material, composite and hydroxyapatite of dentin were calculated to determine the distribution of adhesive infiltration into demineralized dentin. The results were compared with the enamel‐adhesive composite interface. The demineralized zone was smaller in the enamel‐adhesive interface than in the dentin–adhesive interface. The region of collagen‐adhesive crosslinking was wider in the PBNT adhesive than in the SB2 adhesive. However, a gap at the dentin–PBNT composite interface, which was not observed at the dentin–SB2 composite interface, might compromise the dentin–restoration bond. K‐means cluster analysis of the Raman images confirmed the findings. The ultrastructure of the dentin–resin interface was studied using scanning electron microscopy. Small‐angle X‐ray scattering was also applied to reveal and quantify fine‐scale structural features. SB2 adhesive was found to diffuse more into demineralized dentin along with greater nanosized aggregations in the hybrid layer. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman Spectroscopy of Natural Bone and Synthetic Apatites

Abstract

Raman spectroscopy of natural bones and hydroxyapatites is described. In addition, how Raman spectroscopy has proved crucial in providing baseline data for the modification of synthetic apatite powders that are routinely used now as bone replacement materials is explained. It is important to understand the chemical structural properties of natural bone. Bone consists of two primary components: an inorganic or mineral phase, which is mainly a carbonated form of a nanoscale crystalline calcium phosphate, closely resembling hydroxyapatite, and an organic phase, which is composed largely of type I collagen fibers. Other constituents of bone tissue include water and organic molecules such as glycosaminoglycans, glycoproteins, lipids, and peptides. Ions such as sodium, magnesium, fluoride, and citrate are also present, as well as hydrogenophosphate. Hence, the mineral phase in bone may be characterized essentially as nonstoichiometric substituted apatite. Such a distinction is important in the development of synthetic calcium phosphates for application as skeletal implants. An understanding of bone function and its interfacial relationship to an implant clearly depends on the associated structure and composition. Therefore, it is essential to fully understand the chemical composition of bone, and Raman spectroscopy is an excellent technique for such an analysis.     

Surface‐enhanced Raman scattering on colloid gels originated from low molecular weight gelator

Surface‐enhanced Raman scattering (SERS) on silver and gold colloid gels formed by a low molecular weight organic gelator, bis‐(S‐phenylalanine) oxalyl amide, was obtained. Strong Raman signals dominate in the SERS spectra of hydrogels containing silver nanoparticles prepared by citrate and borohydride reduction methods, whereas broad bands of low intensity are detected in the spectra of gold colloid gels. Resemblance between Raman spectrum of the crystalline substance and the SERS spectra of the silver nanoparticle–hydrogel composites implies the electromagnetic nature of the signal enhancement. A change in Raman intensity of the benzene and amide II bands caused by an increase in temperature and concentration indicates that the gelling molecules are strongly attached through the benzene moieties to the metal nanoparticles while participating in gel formation by intermolecular hydrogen bonding between the adjacent oxalyl amide groups. Transmission electron microscopy reveals a dense gel structure in the close vicinity of the enhancing metal particles for both silver colloid gels. Copyright © 2008 John Wiley & Sons, Ltd.     

Structure comparison of Orpiment and Realgar by Raman spectroscopy

Raman spectroscopy was used to characterize and differentiate the two minerals, Orpiment and Realgar, and the bands related to the mineral structure. The Raman spectra of these two minerals are divided into three sections: (a) 100–250?cm^?1 region attributed to the sulfur–arsenic–sulfur bending vibrational modes; (b) 250–450?cm^?1 region due to the arsenic–sulfur stretching vibration; and (c) 450–850?cm^?1 region assigned to overtone and combination bands. A total of 14 Raman bands for the spectrum in the 1600–100?cm^?1 region were observed. The significant differences between the minerals Orpiment and Realgar are observed by Raman spectroscopy. Realgar shows the typical bands observed at 340, 268, 228, and 218?cm^?1, and the special bands at 379, 289, 200, 176, and 102?cm^?1 for Orpiment are observed. The additional bands in 850–450?cm^?1 region are only observed for the mineral Orpiment, which may be attributed to overtone and combination bands in the Raman spectrum. The variation in band positions is dependent upon the structural symmetry, arsenic–sulfur bond distances, and angles. Moreover, another cause for the difference is the effect of the intermolecular forces and to the strong coupling between close lying external and internal modes. The difference of these two minerals structure induce tremendous diversity on Raman spectra, so Raman spectroscopy offers the information on the molecular structure of the minerals Orpiment and Realgar.     

Micro‐Raman spectroscopy and VP‐SEM/EDS applied to the identification of mineral particles and fibres in histological sections

Histological sections of a patient affected by an important respiratory disease were analysed firstly by optical microscope(OM)—crossed polarisers—to identify the presence of incorporated inorganic particles, with particular attention to the fibrous ones. Then, the particles/fibres that were found were studied both with micro‐Raman spectroscopy and variable‐pressure scanning electron microscopy with energy‐dispersive spectroscopy (VP‐SEM/EDS). The two techniques allowed the in situ characterisation of the inorganic phases without disintegration of the organic matter. Micro‐Raman spectroscopy was able to identify the vibrating chemical groups of the mineral phase associated with the inorganic grain while the crystalline structure was preserved by the biological system. The VP‐SEM/EDS characterisation, defining the elemental chemical composition of the analysed particle/fibre, allowed confirmation of the mineral phase deducible from spectroscopic data or its identification with certainty when the spectroscopic data were not exhaustive. Copyright © 2009 John Wiley & Sons, Ltd.     

Minerals from Macedonia. XXII. Laser‐induced fluorescence bands in the FT‐Raman spectrum of almandine mineral

Two strong bands centered at 446 and 607 cm⁻¹ have been observed in the FT‐Raman spectrum of almandine [Fe₃Al₂(SiO₄)₃] excited with 1064 nm, which were completely absent in the corresponding dispersive Raman spectra obtained using 488, 514.5 and 532 nm excitation. Furthermore, the mentioned strong bands have not been registered in the anti‐Stokes side of the FT‐Raman spectrum, and were therefore assigned to laser‐induced fluorescence bands. Their appearance is related to the presence of rare‐earth element traces as impurities in the almandine sample. Additionally, the FT‐Raman (and dispersive Raman) spectrum of the isomorphous spessartine [Mn₃Al₂(SiO₄)₃] mineral has been introduced, which did not show the presence of these fluorescence emission bands. The purity of the minerals was confirmed by study of their powder X‐ray diffraction (PXRD) patterns. Copyright © 2008 John Wiley & Sons, Ltd.     

Vibrational Spectroscopic Characterization of the Arsenate Mineral Barahonaite: Implications for the Molecular Structure

The mineral barahonaite is in all probability a member of the smolianinovite group. The mineral is an arsenate mineral formed as a secondary mineral in the oxidized zone of sulphide deposits. We have studied the barahonaite mineral using a combination of Raman and infrared spectroscopy. The mineral is characterized by a series of Raman bands at 863 cm^?1 with low wavenumber shoulders at 802 and 828 cm^?1. These bands are assigned to the arsenate and hydrogen arsenate stretching vibrations. The infrared spectrum shows a broad spectral profile. Two Raman bands at 506 and 529 cm^?1 are assigned to the triply degenerate arsenate bending vibration (F ₂, ν₄), and the Raman bands at 325, 360, and 399 cm^?1 are attributed to the arsenate ν₂ bending vibration. Raman and infrared bands in the 2500–3800 cm^?1 spectral range are assigned to water and hydroxyl stretching vibrations. The application of Raman spectroscopy to study the structure of barahonaite is better than infrared spectroscopy, probably because of the much higher spatial resolution.     

Amorphous/microcrystalline transition of thick silicon film deposited by PECVD

Thick silicon films were deposited by plasma-enhanced chemical vapor deposition at different plasma power densities. Annealing treatment was performed on these deposited films. As-deposited and annealed films were characterized by X-ray diffraction, Raman scattering spectroscopy and reflectance spectroscopy. Before annealing, only the film deposited at the plasma power density of 500 mW/cm² exhibits a diffraction peak corresponding to the (111) plane orientation. Raman spectrum of this film confirms the presence of crystalline phase. After annealing, a transition from amorphous phase to crystalline one occurs for all samples. This transition is accompanied by an increase of the crystalline fraction volume deduced from Raman spectra analysis and by a reduction of optical gap energy.     

FT‐Raman investigation of human dental enamel surfaces

FT‐Raman spectra of human enamel surfaces from sound, affected (with 1 cavity) and highly affected (with at least 3 cavities) tooth samples were analyzed by principal component analysis (PCA). Major differences between the unaffected and affected tooth samples seem to arise from the structural changes along the c‐axis of hydroxyapatite, the chief crystalline component of human dental enamel. Based on Fisher index calculations, the most discriminative value was obtained for the intensity of the only Raman active ν₂PO₄³⁻ (E₁) symmetric deformation mode at 428 cm⁻¹. Moreover, these changes can be observed through the whole tooth enamel surface, establishing a predisposition to caries correlated to chemical and structural composition of tooth enamel. No spectral changes regarding the CO₃²⁻ substitution were detected by both nondestructive FT‐Raman and FTIR (Fourier transform infrared) spectroscopy of the powdered teeth samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Infrared spectra of urine from cancerous bladders

The infrared spectra of organic constituents of urine from cancerous bladders of some patients were recorded. The spectra of the organic part of the samples were classified into five types according to the bulk constituents. Samples with type A spectra consisted mainly of proteins with only trace amounts of lipids. Their spectra were characterized mainly by the absorption bands of proteins at the frequencies 3330, 3075, 2960, 2850, 1650, 1530, 1450, 1400 and 1320 cm^–1, in addition to a weak band at 1720 cm^–1 due to the absorption of lipids. Samples with type B spectra were characterized by high amounts of proteins and low amounts of lipids and phosphate compounds. The presence of phosphate compounds was indicated by the absorption bands at the frequencies 1100 and 1030 cm^–1. Samples giving spectral type C were characterized by high urea contents as indicated by the presence of two strong bands at 1670 and 1630 cm^–1. Samples with the spectral type D consisted of urea and phosphate compounds whereas the last spectral type E consisted mainly of calcium oxalates, uric acids and phosphate compounds. The presence of calcium oxalates was indicated by the presence of its diagnostic bands at the frequencies 1630 and 1330 cm^–1, while the presence of uric acid was indicated by the bands at the frequencies 1360, 1130, 1020 and 880 cm^–1. On the other hand, the spectra of the organic part of urine from some normal bladders exhibited the characteristic bands of urea only.Careful examination of the spectra of the inorganic part of urine revealed that some samples consisted mainly of hydroxyapatite. The absorption bands of hydroxyapatite appeared at the frequencies 568, 603, 985, 1037 and 1128 cm^–1. The spectra of other samples showed that the bands of basic phosphates at the frequencies 568, 620, 727, 890, 1035 and 1140 cm^–1. The spectra of the inorganic part of urine from a number of normal bladders displayed the bands of basic phosphates. The relationship between urine constituents and pathological types of bladder tumor tissue was discussed.     

Phosphate and amide III mapping in sialoliths with Raman microspectroscopy

Sialoliths, a cause of the salivary gland infection, are reported to be composed of inorganic and organic substances. However, the precise mechanism of sialolith formation remains unclear. The purpose of this report is to elucidate this mechanism by analyzing the precise distribution of phosphate (an inorganic substance) and amide III (an organic substance) in sialoliths by using Raman microspectroscopy. Sialoliths from the submandibular gland duct were analyzed by this form of observation and by a scanning electron microscope (SEM) equipped with an energy‐dispersive X‐ray spectroscope (EDX). In Raman microspectroscopy we analyzed the spectral peak of the phosphate (PO₄³⁻) symmetric stretching vibrational mode (υ₁) at 960 cm⁻¹ and that of amide III at 1265 cm⁻¹ to demonstrate the mapping of an image of these elements showing a semiquantitative distribution of phosphate and amide III in the sialoliths. It was found that phosphate and amide III were concentrated at the center of the sialoliths, and the phosphate distribution in the sialoliths showed concentric laminations. These results indicated the possibility that the sialoliths originated from a nidus of organic materials and progressively grew by the deposition of layers of organic and inorganic materials. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman and surface enhanced Raman scattering of a black dyed silk

The Raman and surface enhanced Raman scattering (SERS) spectra of a black dyed silk sample (BDS) were registered. The spectral analysis was performed on the basis of Raman and SERS spectral data of isolated samples of Bombyx mori silk fibroin, its motif peptide component (GAGAGS) and the synthetic reactive black 5 dye (RB5). The macro FT‐Raman spectrum of the silk sample is consistent with a silk II‐Cp crystalline fraction of Bombyx mori silk fibroin; the SERS spectrum is highly consistent with conformational modifications of the fibroin due to the interactions with the Ag nanoparticles. The GAGAGS peptide sequence dominates the Raman spectrum of the silk. The SERS spectrum of the peptide suggests a random coil conformation imposed by the surface interaction; the serine residue in the new conformation is exposed to the surface. Quantum chemical calculations for a model of the GAGAGS–Ag surface predict a nearly extended conformation at the Ag surface. The Raman spectrum of the dye was analysed, and a complete band assignment was proposed; it was not possible to propose a preferential orientation or organization of the molecule on the metal surface. Quantum chemical calculations for a model of the dye interacting with a silver surface predict a rather coplanar orientation of the RB5 on the Ag metal surface. The Raman spectrum of the BDS sample is dominated by signals from the dye; the general spectral behaviour indicates that the dye mainly interacts with the silk through the sulphone (–SO₂–) and sulphonate (–SO₂–O–) groups. Besides the presence of dye signals, mainly ascribed to the sulphone and sulphonate bands, the SERS spectrum of the BDS sample also displays bands belonging to the amino acids alanine, glycine, serine and particularly tyrosine. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterization of uranium tetrafluoride (UF4) with Raman spectroscopy

The Raman spectrum of uranium tetrafluoride (UF₄) is unambiguously characterized with multiple Raman excitation laser sources for the first time. Across different laser excitation wavelengths, UF₄ demonstrates 16 distinct Raman bands within the 50–400 cm⁻¹ region. The observed Raman bands are representative of various F–F vibrational modes. UF₄ also shows intense fluorescent bands in the 325–750 nm spectral region. Comparison of the UF₄ spectrum with the ZrF₄ spectrum, its crystalline analog, demonstrates a similar Raman band structure consistent with group theory predictions for expected Raman bands. Additionally, a demonstration of combined scanning electron microscopy and in situ Raman spectroscopy microanalytical measurements of UF₄ particulates shows that despite the inherent weak intensity of Raman bands, identification and characterization are possible for micron‐sized particulates with modern instrumentation. The published well‐characterized UF₄ spectrum is extremely relevant to nuclear materials and nuclear safeguard applications. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd.     

Raman and Infrared Spectroscopic Study of the Borate Mineral Kaliborite

We have studied the mineral kaliborite. The sample originated from the Inder B deposit, Atyrau Province, Kazakhstan, and is part of the collection of the Geology Department of the Federal University of Ouro Preto, Minas Gerais, Brazil. The mineral is characterized by a single intense Raman band at 756 cm^?1 assigned to the symmetric stretching modes of trigonal boron. Raman bands at 1229 and 1309 cm^?1 are assigned to hydroxyl in-plane bending modes of boron hydroxyl units. Raman bands are resolved at 2929, 3041, 3133, 3172, 3202, 3245, 3336, 3398, and 3517 cm^?1. These Raman bands are assigned to water stretching vibrations. A very intense sharp Raman band at 3597 cm^?1 with a shoulder band at 3590 cm^?1 is assigned to the stretching vibration of the hydroxyl units. The Raman data are complimented with infrared data and compared with the spectrum of kaliborite downloaded from the Arizona State University database. Differences are noted between the spectrum obtained in this work and that from the Arizona State University database. This research shows that minerals stored in a museum mineral collection age with time. Vibrational spectroscopy enhances our knowledge of the molecular structure of kaliborite.