Origin of micro-scale heterogeneity in polymerisation of photo-activated resin composites

Photo-activated resin composites are widely used in industry and medicine. Despite extensive chemical characterisation, the micro-scale pattern of resin matrix reactive group conversion between filler particles is not fully understood. Using an advanced synchrotron-based wide-field IR imaging system and state-of-the-art Mie scattering corrections, we observe how the presence of monodispersed silica filler particles in a methacrylate based resin reduces local conversion and chemical bond strain in the polymer phase. Here we show that heterogeneity originates from a lower converted and reduced bond strain boundary layer encapsulating each particle, whilst at larger inter-particulate distances light attenuation and monomer mobility predominantly influence conversion. Increased conversion corresponds to greater bond strain, however, strain generation appears sensitive to differences in conversion rate and implies subtle distinctions in the final polymer structure. We expect these findings to inform current predictive models of mechanical behaviour in polymer-composite materials, particularly at the resin-filler interface.

Resin-based-composites are widely used in industry and medicine but the influence of the filler particles on the reactive group conversion in photocurable resins is yet to be elucidated. Here the authors observe reduced local conversion and chemical bond strain in silica filler acrylate composite using synchrotron-based wide-field IR imaging.

Extracting pure absorbance spectra in infrared microspectroscopy by modeling absorption bands as Fano resonances

Midinfrared absorbance spectra obtained from spatially inhomogeneous and finite samples often contain scattering effects characterized by derivative-like bands with shifted peak positions. Such features may be interpreted and accurately modeled by Fano theory when the imaginary part of the complex dielectric function is small and Lorentzian in nature-as is the case for many biological media. Furthermore, by fitting Fano line shapes to isolated absorbance bands, recovery of the peak position and pure absorption strength can be obtained with high accuracy. Additionally, for small and optically soft spherical scatterers, recovery of one or the other of constant refractive index or radius (given approximate knowledge of the other) is possible.

Retinal oxidative stress at the onset of diabetes determined by synchrotron FTIR widefield imaging: towards diabetes pathogenesis

Diabetic retinopathy is a microvascular complication of diabetes that can lead to blindness. In the present study, we aimed to determine the nature of diabetes-induced, highly localized biochemical changes in the neuroretina at the onset of diabetes. High-resolution synchrotron Fourier transform infrared (s-FTIR) wide field microscopy coupled with multivariate analysis (PCA-LDA) was employed to identify biomarkers of diabetic retinopathy with spatial resolution at the cellular level. We compared the retinal tissue prepared from 6-week-old Ins2^Akita/+ heterozygous (Akita/+, N = 6; a model of diabetes) male mice with the wild-type (control, N = 6) mice. Male Akita/+ mice become diabetic at 4-weeks of age. Significant differences (P < 0.001) in the presence of biomarkers associated with diabetes and segregation of spectra were achieved. Differentiating IR bands attributed to nucleic acids (964, 1051, 1087, 1226 and 1710 cm^-1), proteins (1662 and 1608 cm^-1) and fatty acids (2854, 2923, 2956 and 3012 cm^-1) were observed between the Akita/+ and the WT samples. A comparison between distinctive layers of the retina, namely the photoreceptor retinal layer (PRL), outer plexiform layer (OPL), inner nucleus layer (INL) and inner plexiform layer (IPL) suggested that the photoreceptor layer is the most susceptible layer to oxidative stress in short-term diabetes. Spatially-resolved chemical images indicated heterogeneities and oxidative-stress induced alterations in the diabetic retina tissue morphology compared with the WT retina. In this study, the spectral biomarkers and the spatial biochemical alterations in the diabetic retina and in specific layers were identified for the first time. We believe that the conclusions drawn from these studies will help to bridge the gap in our understanding of the molecular and cellular mechanisms that contribute to the pathobiology of diabetic retinopathy.

Estimating and correcting interference fringes in infrared spectra in infrared hyperspectral imaging

Short-term acclimation response of individual cells of Thalassiosira weissflogii was monitored by Synchrotron FTIR imaging over the span of 75 minutes. The cells, collected from batch cultures, were maintained in a constant flow of medium, at an irradiance of 120 μmol m-2 s-1 and at 20 °C. Multiple internal reflections due to the micro fluidic channel were modeled, and showed that fringes are additive sinusoids to the pure absorption of the other components of the system. Preprocessing of the hyperspectral cube (x, y, Abs(λ)) included removing spectral fringe using an EMSC approach. Principal component analysis of the time series of hyperspectral cubes showed macromolecular pool variations (carbohydrates, lipids and DNA/RNA) of less than 2% after fringe correction.

Highlighting IR Spectrochemical Imaging of the Retina

An emerging application of mid-IR spectrochemical imaging of the retina is its utility in studying the highly localized biomolecular alterations in the chemistry of retinal cell layers associated with several pathological conditions. Spatially resolved IR images highlight simultaneous chemical composition of the entire span of the retina in a label-free manner.

Synchrotron-Based Three-Dimensional Fourier-Transform Infrared Spectro-Microtomography of Murchison Meteorite Grain

We demonstrate nondestructive, three-dimensional, microscopic, infrared (IR) spectral in-situ imaging of an extraterrestrial sample. Spatially resolved chemical composition and spatial correlations are investigated within a single 45 µm grain of the Murchison meteorite. Qualitative and quantitative investigation through this analytical technique can help elucidate the origin and evolution of meteoritic compounds as well as parent body processes without damaging or altering the investigated samples.

Thermal source Fourier transform infrared microtomography applied to Arctic sea ice diatoms

We have used thermal source Fourier Transform Infrared (FTIR) microtomographic imaging to compare sea ice diatoms growing under different light conditions. A prototype tomography accessory was designed to have sufficient degrees of freedom to align any tilted cylindrical sample relative to the axis of rotation, minimizing the off-axis path traced during rotation. The lightweight device rests on the motorized stage to position the sample in the field-of-view and enable mosaic imaging. Reconstruction routines were tested with simulated and real phantoms, to assess limitations in the Radon back-projection method employed. The distribution and abundance of biochemicals is analysed for targets larger than a single FPA tile. Two and three dimensional (2D and 3D) FTIR spectrochemical images were obtained with a Focal Plane Array (FPA, nominal 1.1 μm pixel edges) for phantoms (polystyrene beads in polyvinyl alcohol matrix) and diatom cells harvested from land fast, first-year ice sites in Resolute Passage (74 43.628'N; 95 33.330'W) and Dease Strait (69° 1.11'N; 105° 21.29'W), Nunavut, Canada. The analysis of relative concentrations of organic matter within the encapsulating silica frustules of diatoms is important for a better understanding of both the physiological state and the individual cellular response to environmental pressures. Analysis of 3D FTIR images of Nitzschia frigida collected from beneath high (17-19 cm) and low (3-7 cm) snow depth revealed higher concentrations of lipids in diatoms collected under low snow cover, uniquely based on spectroscopically determined total 3D cell volume and biochemical content.

Quantifying Biochemical Alterations in Brown and Subcutaneous White Adipose Tissues of Mice Using Fourier Transform Infrared Widefield Imaging

Stimulating increased thermogenic activity in adipose tissue is an important biological target for obesity treatment, and label-free imaging techniques with the potential to quantify stimulation-associated biochemical changes to the adipose tissue are highly sought after. In this study, we used spatially resolved Fourier transform infrared (FTIR) imaging to quantify biochemical changes caused by cold exposure in the brown and subcutaneous white adipose tissues (BAT and s-WAT) of 6 week-old C57BL6 mice exposed to 30°C (N = 5), 24°C (N = 5), and 10°C (N = 5) conditions for 10 days. Fat exposed to colder temperatures demonstrated greater thermogenic activity as indicated by increased messenger RNA expression levels of a panel of thermogenic marker genes including uncoupling protein 1 (UCP-1) and Dio2. Protein to lipid ratio, calculated from the ratio of the integrated area from 1,600 to 1,700 cm^-1 (amide I) to the integrated area from 2,830 to 2,980 cm^-1 (saturated lipids), was elevated in 10°C BAT and s-WAT compared to 24°C (p = 0.004 and p < 0.0001) and 30°C (p = 0.0033 and p < 0.0001). Greater protein to lipid ratio was associated with greater UCP-1 expression level in the BAT (p = 0.021) and s-WAT (p = 0.032) and greater Dio2 expression in s-WAT (p = 0.033). The degree of unsaturation, calculated from the ratio of the integrated area from 2,992 to 3,020 cm^-1 (unsaturated lipids) to the integrated area from 2,830 to 2,980 cm^-1 (saturated lipids), showed stepwise decreases going from colder-exposed to warmer-exposed BAT. Complementary ¹H NMR measurements confirmed the findings from this ratio in BAT. Principal component analysis applied to FTIR spectra revealed pronounced differences in overall spectral characteristics between 30, 24, and 10°C BAT and s-WAT. Spatially resolved FTIR imaging is a promising technique to quantify cold-induced biochemical changes in BAT and s-WAT in a label-free manner.

Diagnosing malaria infected cells at the single cell level using focal plane array Fourier transform infrared imaging spectroscopy

New methods are needed to rapidly identify malaria parasites in blood smears. The coupling of a Focal Plane Array (FPA) infrared microscope system to a synchrotron light source at IRENI enables rapid molecular imaging at high spatial resolution. The technique, in combination with hyper-spectral processing, enables imaging and diagnosis of early stage malaria parasites at the single cell level in a blood smear. The method relies on the detection of distinct lipid signatures associated with the different stages of the malaria parasite and utilises resonant Mie extended multiplicative scatter correction to pre-process the spectra followed by full bandwidth image deconvolution to resolve the single cells. This work demonstrates the potential of focal plane technology to diagnose single cells in a blood smear. Brighter laboratory based infrared sources, optical refinements and higher sensitive detectors will soon see the emergence of focal plane array imaging in the clinical environment.

Cold shock induces apoptosis of dorsal root ganglion neurons plated on infrared windows

The chemical status of live sensory neurons is accessible with infrared microspectroscopy of appropriately prepared cells. In this paper, individual dorsal root ganglion (DRG) neurons have been prepared with two different protocols, and plated on glass cover slips, BaF2 and CaF2 substrates. The first protocol exposes the intact DRGs to 4 °C for between 20-30 minutes before dissociating individual neurons and plating 2 hours later. The second protocol maintains the neurons at 23 °C for the entire duration of the sample preparation. The visual appearance of the neurons is similar. The viability was assessed by means of trypan blue exclusion method to determine the viability of the neurons. The neurons prepared under the first protocol (cold exposure) and plated on BaF2 reveal a distinct chemical signature and chemical distribution that is different from the other sample preparations described in the paper. Importantly, results for other sample preparation methods, using various substrates and temperature protocols, when compared across the overlapping spectral bandwidth, present normal chemical distribution within the neurons. The unusual chemically specific spatial variation is dominated by a lack of protein and carbohydrates in the center of the neurons and signatures of unraveling DNA are detected. We suggest that cold shock leads to apoptosis of DRGs, followed by osmotic stress originating from ion gradients across the cell membrane leading to cell lysis.

Correction: Cold shock induces apoptosis of dorsal root ganglion neurons plated on infrared windows

Correction for ‘Cold shock induces apoptosis of dorsal root ganglion neurons plated on infrared windows’ by Ebrahim Aboualizadeh et al., Analyst, 2015, 140, 4046–4056.

Multifunctional supramolecular polymer networks as next-generation consolidants for archaeological wood conservation

The preservation of our cultural heritage is of great importance to future generations. Despite this, significant problems have arisen with the conservation of waterlogged wooden artifacts. Three major issues facing conservators are structural instability on drying, biological degradation, and chemical degradation on account of Fe(3+)-catalyzed production of sulfuric and oxalic acid in the waterlogged timbers. Currently, no conservation treatment exists that effectively addresses all three issues simultaneously. A new conservation treatment is reported here based on a supramolecular polymer network constructed from natural polymers with dynamic cross-linking formed by a combination of both host-guest complexation and a strong siderophore pendant from a polymer backbone. Consequently, the proposed consolidant has the ability to chelate and trap iron while enhancing structural stability. The incorporation of antibacterial moieties through a dynamic covalent linkage into the network provides the material with improved biological resistance. Exploiting an environmentally compatible natural material with completely reversible chemistries is a safer, greener alternative to current strategies and may extend the lifetime of many culturally relevant waterlogged artifacts around the world.

Chemical structure and morphology of dorsal root ganglion neurons from naive and inflamed mice

Fourier transform infrared spectromicroscopy provides label-free imaging to detect the spatial distribution of the characteristic functional groups in proteins, lipids, phosphates, and carbohydrates simultaneously in individual DRG neurons. We have identified ring-shaped distributions of lipid and/or carbohydrate enrichment in subpopulations of neurons which has never before been reported. These distributions are ring-shaped within the cytoplasm and are likely representative of the endoplasmic reticulum. The prevalence of chemical ring subtypes differs between large- and small-diameter neurons. Peripheral inflammation increased the relative lipid content specifically in small-diameter neurons, many of which are nociceptive. Because many small-diameter neurons express an ion channel involved in inflammatory pain, transient receptor potential ankyrin 1 (TRPA1), we asked whether this increase in lipid content occurs in TRPA1-deficient (knock-out) neurons. No statistically significant change in lipid content occurred in TRPA1-deficient neurons, indicating that the inflammation-mediated increase in lipid content is largely dependent on TRPA1. Because TRPA1 is known to mediate mechanical and cold sensitization that accompanies peripheral inflammation, our findings may have important implications for a potential role of lipids in inflammatory pain.

Toward optimal spatial and spectral quality in widefield infrared spectromicroscopy of IR labelled single cells

Advancements in widefield infrared spectromicroscopy have recently been demonstrated following the commissioning of IRENI (InfraRed ENvironmental Imaging), a Fourier Transform infrared (FTIR) chemical imaging beamline at the Synchrotron Radiation Center. The present study demonstrates the effects of magnification, spatial oversampling, spectral pre-processing and deconvolution, focusing on the intracellular detection and distribution of an exogenous metal tris-carbonyl derivative 1 in a single MDA-MB-231 breast cancer cell. We demonstrate here that spatial oversampling for synchrotron-based infrared imaging is critical to obtain accurate diffraction-limited images at all wavelengths simultaneously. Resolution criteria and results from raw and deconvoluted images for two Schwarzschild objectives (36×, NA 0.5 and 74×, NA 0.65) are compared to each other and to prior reports for raster-scanned, confocal microscopes. The resolution of the imaging data can be improved by deconvolving the instrumental broadening that is determined with the measured PSFs, which is implemented with GPU programming architecture for fast hyperspectral processing. High definition, rapidly acquired, FTIR chemical images of respective spectral signatures of the cell 1 and shows that 1 is localized next to the phosphate- and Amide-rich regions, in agreement with previous infrared and luminescence studies. The infrared image contrast, localization and definition are improved after applying proven spectral pre-processing (principal component analysis based noise reduction and RMie scattering correction algorithms) to individual pixel spectra in the hyperspectral cube.

Synchrotron FTIR reveals lipid around and within amyloid plaques in transgenic mice and Alzheimer's disease brain

While the basis of neuronal degeneration in Alzheimer's disease (AD) continues to be debated, the amyloid cascade hypothesis remains central. Amyloid plaques are a required pathological marker for post mortem diagnosis, and Aβ peptide is regarded by most as a critical trigger at the very least. We present spectrochemical image analysis of brain tissue sections obtained with the mid-infrared beamline IRENI (InfraRed ENvironmental Imaging, Synchrotron Radiation Center, U Wisconsin-Madison), where the pixel resolution of 0.54 × 0.54 µm(2) permits analysis at sub-cellular dimensions. Spectrochemical images of dense core plaque found in hippocampus and cortex sections of two transgenic mouse models of AD (TgCRND8 and 3×Tg) are compared with plaque images from a 91 year old apoE43 human AD case. Spectral analysis was done in conjunction with histochemical stains of serial sections. A lipid membrane-like spectral signature surrounded and infiltrated the dense core plaques in all cases. Remarkable compositional similarities in early stage plaques suggest similar routes to plaque formation, regardless of genetic predisposition or mammalian origin.

3D spectral imaging with synchrotron Fourier transform infrared spectro-microtomography

We report Fourier transform infrared spectro-microtomography, a nondestructive three-dimensional imaging approach that reveals the distribution of distinctive chemical compositions throughout an intact biological or materials sample. The method combines mid-infrared absorption contrast with computed tomographic data acquisition and reconstruction to enhance chemical and morphological localization by determining a complete infrared spectrum for every voxel (millions of spectra determined per sample).

Multiple morphologies of gold-magnetite heterostructure nanoparticles are effectively functionalized with protein for cell targeting

Nanoparticles composed of a magnetic iron oxide core surrounded by a metal shell have utility in a broad range of biomedical applications. However, the presence of surface energy differences between the two components makes wetting of oxide with metal unfavorable, precluding a "core-shell" structure of an oxide core completely surrounded by a thin metal shell. Three-dimensional island growth followed by island coalescence into thick shells is favored over the two-dimensional layer-by-layer growth of a thin, continuous metal coating of a true core-shell. Aqueous synthesis of gold-coated magnetite nanoparticles with analysis by infrared, energy-dispersive X-ray, and electron energy loss spectroscopies; high-resolution transmission electron microscopy; selected area electron diffraction; and high-angle annular dark-field scanning transmission electron microscopy showed two distinct morphologies that are inconsistent with an idealized core-shell. The majority were isolated ~16-22-nm-diameter nanoparticles consisting of ~7-nm-diameter magnetite and a thick deposition of gold, most often discontinuous, with some potentially "sandwiched" morphologies. A minority were aggregates of agglomerated magnetite decorated with gold but displaying significant bare magnetite. Both populations were successfully conjugated to fibrinogen and targeted to surface-activated platelets, demonstrating that iron oxide-gold nanoparticles produced by aqueous synthesis do not require an ideal core-shell structure for biological activity in cell labeling and targeting applications.

High-spatial-resolution mapping of superhydrophobic cicada wing surface chemistry using infrared microspectroscopy and infrared imaging at two synchrotron beamlines

The wings of some insects, such as cicadae, have been reported to possess a number of interesting and unusual qualities such as superhydrophobicity, anisotropic wetting and antibacterial properties. Here, the chemical composition of the wings of the Clanger cicada (Psaltoda claripennis) were characterized using infrared (IR) microspectroscopy. In addition, the data generated from two separate synchrotron IR facilities, the Australian Synchrotron Infrared Microspectroscopy beamline (AS-IRM) and the Synchrotron Radiation Center (SRC), University of Wisconsin-Madison, IRENI beamline, were analysed and compared. Characteristic peaks in the IR spectra of the wings were assigned primarily to aliphatic hydrocarbon and amide functionalities, which were considered to be an indication of the presence of waxy and proteinaceous components, respectively, in good agreement with the literature. Chemical distribution maps showed that, while the protein component was homogeneously distributed, a significant degree of heterogeneity was observed in the distribution of the waxy component, which may contribute to the self-cleaning and aerodynamic properties of the cicada wing. When comparing the data generated from the two beamlines, it was determined that the SRC IRENI beamline was capable of producing higher-spatial-resolution distribution images in a shorter time than was achievable at the AS-IRM beamline, but that spectral noise levels per pixel were considerably lower on the AS-IRM beamline, resulting in more favourable data where the detection of weak absorbances is required. The data generated by the two complementary synchrotron IR methods on the chemical composition of cicada wings will be immensely useful in understanding their unusual properties with a view to reproducing their characteristics in, for example, industry applications.

Mechanistic insights into nanotoxicity determined by synchrotron radiation-based Fourier-transform infrared imaging and multivariate analysis

Our ability to identify the mechanisms by which carbon-based nanomaterials (CBNs) exert toxicity in cells is constrained by the lack of standardized methodologies to assay endpoint effects. Herein we describe a method of mechanistically identifying the effects of various CBN types in both prokaryotic and eukaryotic cells using multi-beam synchrotron radiation-based Fourier-transform infrared imaging (SR-FTIRI) at diffraction-limited resolution. This technique overcomes many of the inherent difficulties of assaying nanotoxicity and demonstrates exceptional sensitivity in identifying the effects of CBNs in cells at environmentally-relevant concentrations. We identify key mechanisms of nanotoxicity as the alteration of Amide and lipid biomolecules, but propose more specific bioactivity of CBNs occurs as a result of specific interactions between CBN structural conformation and cellular characteristics.

Ag nanocrystal as a promoter for carbon nanotube-based room-temperature gas sensors

We have investigated the room-temperature sensing enhancement of Ag nanoparticles (NPs) for multiwalled carbon nanotube (MWCNT)-based gas sensors using electrical measurements, in situ infrared (IR) microspectroscopy, and density functional theory (DFT) calculations. Multiple hybrid nanosensors with structures of MWCNTs/SnO(2)/Ag and MWCNTs/Ag have been synthesized using a process that combines a simple mini-arc plasma with electrostatic force directed assembly, and characterized by electron microscopy techniques. Ag NPs were found to enhance the sensing behavior through the "electronic sensitization" mechanism. In contrast to sensors based on bare MWCNTs and MWCNTs/SnO(2), sensors with Ag NPs show not only higher sensitivity and faster response to NO(2) but also significantly enhanced sensitivity to NH(3). Our DFT calculations indicate that the increased sensitivity to NO(2) is attributed to the formation of a NO(3) complex with oxygen on the Ag surface accompanying a charge rearrangement and a net electron transfer from the hybrid to NO(2). The significant response to NH(3) is predicted to arise because NH(3) is attracted to hollow sites on the oxidized Ag surface with the H atoms pointing towards Ag atoms and electron donation from H to the hybrid sensor.

Fourier transform infrared spectrochemical imaging: review of design and applications with a focal plane array and multiple beam synchrotron radiation source

The beamline design, microscope specifications, and initial results from the new mid-infrared beamline (IRENI) are reviewed. Synchrotron-based spectrochemical imaging, as recently implemented at the Synchrotron Radiation Center in Stoughton, Wisconsin, demonstrates the new capability to achieve diffraction limited chemical imaging across the entire mid-infrared region, simultaneously, with high signal-to-noise ratio. IRENI extracts a large swath of radiation (320 hor. × 25 vert. mrads(2)) to homogeneously illuminate a commercial infrared (IR) microscope equipped with an IR focal plane array (FPA) detector. Wide-field images are collected, in contrast to single-pixel imaging from the confocal geometry with raster scanning, commonly used at most synchrotron beamlines. IRENI rapidly generates high quality, high spatial resolution data. The relevant advantages (spatial oversampling, speed, sensitivity, and signal-to-noise ratio) are discussed in detail and demonstrated with examples from a variety of disciplines, including formalin-fixed and flash-frozen tissue samples, live cells, fixed cells, paint cross-sections, polymer fibers, and novel nanomaterials. The impact of Mie scattering corrections on this high quality data is shown, and first results with a grazing angle objective are presented, along with future enhancements and plans for implementation of similar, small-scale instruments.

Evidence of nanocrystalline semiconducting graphene monoxide during thermal reduction of graphene oxide in vacuum

As silicon-based electronics are reaching the nanosize limits of the semiconductor roadmap, carbon-based nanoelectronics has become a rapidly growing field, with great interest in tuning the properties of carbon-based materials. Chemical functionalization is a proposed route, but syntheses of graphene oxide (G-O) produce disordered, nonstoichiometric materials with poor electronic properties. We report synthesis of an ordered, stoichiometric, solid-state carbon oxide that has never been observed in nature and coexists with graphene. Formation of this material, graphene monoxide (GMO), is achieved by annealing multilayered G-O. Our results indicate that the resulting thermally reduced G-O (TRG-O) consists of a two-dimensional nanocrystalline phase segregation: unoxidized graphitic regions are separated from highly oxidized regions of GMO. GMO has a quasi-hexagonal unit cell, an unusually high 1:1 O:C ratio, and a calculated direct band gap of ∼0.9 eV.

Demountable liquid/flow cell for in vivo infrared microspectroscopy of biological specimens

We have developed a liquid/flow cell/chamber allowing infrared measurements of living biological specimens with high spatial resolution under a controlled aqueous environment. This flow chamber features sub-micrometer thick diamond windows exhibiting low spherical and chromatic aberrations. Diamond has excellent transmission properties and minimal dispersion over the entire mid-infrared and visible spectral ranges. In contrast to current commercially available infrared liquid chambers, the flow chamber has a slim profile, which accommodates high resolution/magnification microscope objectives with small working distances, down to 0.6 mm above the chamber and 6 mm below the flow chamber. We have coupled a pump to the flow chamber to provide medium exchange. As an example, we present microspectroscopic infrared maps and spectra of the freshwater green alga Micrasterias sp. in the new flow chamber and compare them to maps obtained with a conventional liquid chamber. Pulse-amplitude-modulated fluorescence measurements on Micrasterias sp. cells inside the new flow chamber have been evaluated to demonstrate the viability of the algal cells.

Characterization of articular calcium-containing crystals by synchrotron FTIR

OBJECTIVE

Sixty percent of synovial fluids from patients with severe osteoarthritis (OA) contain calcium pyrophosphate dihydrate (CPPD) or basic calcium phosphate (BCP) crystals. These bioactive crystals can be particularly difficult to accurately identify in complex biologic systems, such as in vitro models of crystal formation. We sought to determine if synchrotron Fourier Transform Infrared spectroscopy (sFTIR) could be used to identify and characterize calcium-containing crystals in mineralization models.

METHODS

CPPD and BCP crystals from porcine models of crystal formation were examined with an FTIR Microscope attached to a synchrotron light source. As a comparison, crystals from human synovial fluids were also examined. The sFTIR spectra generated were compared with known spectra of multiple forms of BCP and CPPD crystals, as well as spectra generated by synthetic CPPD and BCP crystals and cartilage proteoglycans, alone and in mixtures.

RESULTS

sFTIR readily identified CPPD and BCP crystals in porcine models as well as in fresh synovial fluids. Brushite was also present in human and porcine samples, and whitlockite was seen in some porcine samples. Mixtures of minerals were commonly found in a single crystal aggregate in both human and porcine samples. In spectra from many CPPD crystals, the peak at the 1134 cm(-1) found on the standard spectrum for CPPD was diminished. Addition of spectra from cartilage proteoglycans to those of synthetic CPPD crystals dampened the peak at this frequency region, much as this peak was diminished in biologically derived CPPD crystals.

CONCLUSION

sFTIR analysis allows for accurate identification of CPPD and BCP crystals generated in vitro and will be a useful research tool to study articular crystals.

Homeostasis of cell composition during prolonged darkness

The chemical composition of organisms in relation to their environmental resource availability is an area of intense research activity. We studied the changes in cell composition of the cyanobacterium Phormidium autumnale in response to prolonged darkness. Cells allocated their internal resources in a homeostatic manner, oxidizing all the three major cellular constituents in a proportional way. This resulted in constant C/N and carbohydrates, lipids and proteins ratios that remained unaltered throughout the whole incubation period. We propose the maintenance of balanced cell composition (homeostasis) as an evolutionary strategy related to environmental transitory changes.

Two-mirror wave-front-dividing interferometer for infrared synchrotron radiation

We describe what is to our knowledge the first instrument specifically designed for use with infrared synchrotron radiation that takes advantage of the spatial coherence of this radiation. Beam splitting is achieved by wave-front division. We show data taken with the instrument over the wavelength region from 10 to 1000 microm (1-mm wavelengths) and discuss the advantages of this instrument over a conventional one.

Infrared properties of single crystal MgO, a substrate for high temperature superconducting films

We report and analyze the infrared properties of single crystal MgO, an important substrate for high T(c), superconducting films, from 10 to 280 cm(-1) and 20-300 K.