Adding synchrotron radiation to infrared microspectroscopy: what's new in biomedical applications?

Step-scan IR spectroelectrochemistry with ultramicroelectrodes: nonsurface enhanced detection of near femtomole quantities using synchrotron radiation

The result of interfacing step-scan spectroelectrochemistry with an IR microscope and synchrotron infrared (SIR) radiation is provided here. An external reflectance cell containing a 25 μm gold ultramicroelectrode is employed to achieve an electrochemical time constant less than one microsecond. The use of a prototypical electrochemical system, i.e., the mass-transport controlled reduction of ferricyanide, allows for a proof of principle evaluation of the viability of SIR for step-scan spectroelectrochemistry. An analysis of the importance of accounting for synchrotron source variation over the prolonged duration of a step-scan experiment is provided. Modeling of the material flux in the restricted diffusion space afforded by the external reflectance cell allows the quantitative IR results to be compared to theoretical predictions. The results indicate that only at very short times does linear diffusion within the cavity dominate the electrode response and the majority of the transient signal operates under conditions of quasi-hemispherical diffusion. The analytical information provided by the IR signal is found to be considerably less than that derived from the current response due the latter's pronounced edge effects. The results provide a detection limit of 36 fmol for step-scan SIR measurements of ferrocyanide. Implications for future IR spectroelectrochemical studies in the microsecond domain are discussed.

Differences in the hippocampal frequency of creatine inclusions between the acute and latent phases of pilocarpine model defined using synchrotron radiation-based FTIR microspectroscopy

Temporal lobe epilepsy (TLE) is the most common type of epilepsy in adults. Of the animal models developed to investigate the pathogenesis of TLE, the one with pilocarpine-induced seizures is most often used. After pilocarpine administration in animals, three distinct periods--acute, latent, and chronic--can be distinguished according to their behavior. The present paper is the continuation of our previous study which has shown an increased occurrence of creatine inclusions in rat hippocampal formations from the acute phase of pilocarpine-induced status epilepticus (SE) and positive correlation between their quantity and the total time of seizure activity within the observation period. In this paper, we tried to verify if anomalies in hippocampal creatine accumulation were the temporary or permanent effect of pilocarpine-evoked seizures. To realize this purpose, male Wistar rats in the latent phase (3 days after pilocarpine administration) were examined. The results obtained for the period when stabilization of animal behavior and EEG occurs were afterwards compared with ones obtained for the acute phase of pilocarpine-induced SE and for naive controls. To investigate the frequency of creatine inclusions within the hippocampal formation as well as in its selected areas (sectors 1-3 of Ammon's horn (CA1-CA3), dentate gyrus (DG), and hilus of DG) and cellular layers (pyramidal, molecular, multiform, and granular cell layers), synchrotron radiation-based Fourier-transform infrared microspectroscopy was used. The applied technique, being a combination of light microscopy and infrared spectroscopy, allowed us to localize microscopic details in the analyzed samples and provided information concerning their chemical composition. Moreover, the use of a synchrotron source of IR radiation allowed us to carry out the research at the diffraction-limited spatial resolution which, because of the typical size of creatine inclusions (from a few to dozens of micrometers), was necessary for our study. The comparison of epileptic animals in the latent phase with controls showed statistically significant increase in the number of creatine inclusions for most of the analyzed hippocampal regions, all examined cellular layers, as well as the whole hippocampal formation. Moreover, for the hilus of the DG and CA3 area, the number of creatine deposits was higher in the latent than in the acute phase after pilocarpine injection. In light of the obtained results, an anomaly in the hippocampal accumulation of creatine is the long-term effect of pilocarpine-evoked seizures, and the intensity of this phenomenon may increase with time passing from the primary injury.

Near-field imaging and nano-Fourier-transform infrared spectroscopy using broadband synchrotron radiation

We demonstrate scanning near-field optical microscopy with a spatial resolution below 100 nm by using low intensity broadband synchrotron radiation in the IR regime. The use of such a broadband radiation source opens up the possibility to perform nano-Fourier-transform infrared spectroscopy over a wide spectral range.

Profiling pluripotent stem cells and organelles using synchrotron radiation infrared microspectroscopy

FTIR micro-spectroscopy is a sensitive, non-destructive and label-free method offering diffraction-limited resolution with high signal-to-noise ratios when combined with a synchrotron radiation source. The vibrational signature of individual cells was used to validate an alternative strategy for reprogramming induced pluripotent stem cells generated from amniocytes. The iPSC lines PB09 and PB10, were reprogrammed from the same amniocyte cell line using respectively the Oct54, Sox2, Lin28, and Nanog and the Oct4 and Sox2 transcription factor cocktail. We show that cells reprogrammed by the two different sets of transfection factors have similar spectral signatures after reprogramming, except for a small subpopulation of cells in one of the cell lines. Mapping HeLa cells at subcellular resolution, we show that the Golgi apparatus, the cytoplasm and the nucleus have a specific spectral signature. The CH(3):CH(2) ratio is the highest in the nucleus and the lowest in the Golgi apparatus/endoplasmic reticulum, in agreement with the membrane composition of these organelles. This is confirmed by specific staining of the organelles with fluorescent dyes. Subcellular differentiation of cell compartments is also demonstrated in living cells.

A framework for far-field infrared absorption microscopy beyond the diffraction limit

A framework is proposed for infrared (IR) absorption microscopy in the far-field with a spatial resolution below the diffraction limit. The sub-diffraction resolution is achieved by pumping a transient contrast in the population of a selected vibrational mode with IR pulses that exhibit alternating central minima and maxima, and by probing the corresponding absorbance at the same wavelength with adequately delayed Gaussian pulses. Simulations have been carried out on the basis of empirical parameters emulating patterned thin films of octadecyltrichlorosilane and a resolution of 250 nm was found when probing the CH₂ stretches at 3.5 μm with pump energies less than ten times the vibrational saturation threshold.

The effect of optical substrates on micro-FTIR analysis of single mammalian cells

The study of individual cells with infrared (IR) microspectroscopy often requires living cells to be cultured directly onto a suitable substrate. The surface effect of the specific substrates on the cell growth—viability and associated biochemistry—as well as on the IR analysis—spectral interference and optical artifacts—is all too often ignored. Using the IR beamline, MIRIAM (Diamond Light Source, UK), we show the importance of the substrate used for IR absorption spectroscopy by analyzing two different cell lines cultured on a range of seven optical substrates in both transmission and reflection modes. First, cell viability measurements are made to determine the preferable substrates for normal cell growth. Successively, synchrotron radiation IR microspectroscopy is performed on the two cell lines to determine any genuine biochemically induced changes or optical effect in the spectra due to the different substrates. Multivariate analysis of spectral data is applied on each cell line to visualize the spectral changes. The results confirm the advantage of transmission measurements over reflection due to the absence of a strong optical standing wave artifact which amplifies the absorbance spectrum in the high wavenumber regions with respect to low wavenumbers in the mid-IR range. The transmission spectra reveal interference from a more subtle but significant optical artifact related to the reflection losses of the different substrate materials. This means that, for comparative studies of cell biochemistry by IR microspectroscopy, it is crucial that all samples are measured on the same substrate type.

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In situ chemical composition analysis of cirrhosis by combining synchrotron fourier transform infrared and synchrotron X-ray fluorescence microspectroscopies on the same tissue section

Liver is subject to various chronic pathologies, progressively leading to cirrhosis, which is associated with an increased risk of hepatocellular carcinoma. There is an urgent need for diagnostic and prognostic markers of chronic liver diseases and liver cancer. Spectroscopy-based approaches can provide an overview of the chemical composition of a tissue sample offering the possibility of investigating in depth the subtle chemical changes associated with pathological states. In this study, we have addressed the composition of cirrhotic liver tissue by combining synchrotron Fourier transform infrared (FTIR) microspectroscopy and synchrotron micro-X-ray fluorescence (XRF) on the same tissue section using a single sample holder in copper. This allowed investigation of the in situ biochemical as well as elemental composition of cells and tissues at high spatial resolution. Cirrhosis is characterized by regeneration nodules surrounded by annular fibrosis. Hepatocytes within cirrhotic nodules were characterized by high content in esters and sugars as well as in phosphorus and iron compared with fibrotic septa. A high heterogeneity was observed between cirrhotic nodules in their content in sugars and iron. On fibrosis, synchrotron XRF revealed enrichment in calcium compared to cirrhotic hepatocytes. Careful scrutiny of tissue sections led to detection of the presence of microcrystals that were demonstrated as precipitates of calcite using synchrotron FTIR. These results demonstrated that synchrotron FTIR and synchrotron XRF microspectroscopies provide complementary information on the chemical composition of cirrhotic hepatocytes and fibrotic septa in cirrhosis.

Microbeam-irradiated tumour tissue possesses a different infrared absorbance profile compared to broad beam and sham-irradiated tissue

PURPOSE

To investigate biochemical changes in mouse tumour tissue following Microbeam Radiation Therapy (MRT) and Broad Beam (BB) irradiation using synchrotron Fourier-Transform Infrared (FTIR) microspectroscopy.

MATERIALS AND METHODS

Synchrotron FTIR microspectroscopy was carried out on mouse tumour sections previously irradiated with BB (11, 22 or 44 Gy), MRT (560 Gy in-beam, 25 μm wide, 200 μm peak separation) or sham-irradiation (0 Gy) from mice culled 4 hours post-irradiation.

RESULTS

MRT and BB-irradiated tumour sections showed clear chemical shifts in spectral bands corresponding to functional group vibrations in protein (1654-1630 cm(-1)), lipid (~1470, 1463 cm(-1)) and nucleic acid (1130-1050 cm(-1)). MRT peak and valley regions showed virtually identical absorbance patterns in protein and lipid regions. However, we observed chemical shifts corresponding to the nucleic acid region (1120-1050 cm(-1)) between the peak and valley dose regions. Chemical maps produced from integrating absorbance bands of interest over the scanned tumour area did not reveal any microbeam paths.

CONCLUSIONS

The lack of difference between MRT peak and valley irradiated areas suggests a holistic tissue response to MRT that occurs within 4 h, and might be the first evidence for a mechanism by which MRT kills the whole tumour despite only a small percentage receiving peak irradiation.

Synchrotron ultraviolet microspectroscopy on rat cortical bone: involvement of tyrosine and tryptophan in the osteocyte and its environment

Alcohol induced osteoporosis is characterized by a bone mass decrease and microarchitecture alterations. Having observed an excess in osteocyte apoptosis, we aimed to assess the bone tissue biochemistry, particularly in the osteocyte and its environment. For this purpose, we used a model of alcohol induced osteoporosis in rats. Bone sections of cortical bone were investigated using synchrotron UV-microspectrofluorescence at subcellular resolution. We show that bone present three fluorescence peaks at 305, 333 and 385 nm, respectively corresponding to tyrosine, tryptophan and collagen. We have determined that tyrosine/collagen and tryptophan/collagen ratios were higher in the strong alcohol consumption group. Tryptophan is related to the serotonin metabolism involved in bone formation, while tyrosine is involved in the activity of tyrosine kinases and phosphatases in osteocytes. Our experiment represents the first combined synchrotron UV microspectroscopy analysis of bone tissue with a quantitative biochemical characterization in the osteocyte and surrounding matrix performed separately.

A study of Ganoderma lucidum spores by FTIR microspectroscopy

In order to obtain unique information of Ganoderma lucidum spores, FTIR microspectroscopy was used to study G. lucidum spores from Anhui Province (A), Liaoning Province (B) and Shangdong Province (C) of China. IR micro-spectra were acquired with high-resolution and well-reproducibility. The IR spectra of G. lucidum spores from different areas were similar and mainly made up of the absorption bands of polysaccharide, sterols, proteins, fatty acids, etc. The results of curve fitting indicated the protein secondary structures were dissimilar among the above G. lucidum spores. To identify G. lucidum spores from different areas, the H1078/H1640 value might be a potentially useful factor, furthermore FTIR microspectroscopy could realize this identification efficiently with the help of hierarchical cluster analysis. The result indicates FTIR microspectroscopy is an efficient tool for identification of G. lucidum spores from different areas. The result also suggests FTIR microspectroscopy is a potentially useful tool for the study of TCM.

Identification of spectral modifications occurring during reprogramming of somatic cells

Recent technological advances in cell reprogramming by generation of induced pluripotent stem cells (iPSC) offer major perspectives in disease modelling and future hopes for providing novel stem cells sources in regenerative medicine. However, research on iPSC still requires refining the criteria of the pluripotency stage of these cells and exploration of their equivalent functionality to human embryonic stem cells (ESC). We report here on the use of infrared microspectroscopy to follow the spectral modification of somatic cells during the reprogramming process. We show that induced pluripotent stem cells (iPSC) adopt a chemical composition leading to a spectral signature indistinguishable from that of embryonic stem cells (ESC) and entirely different from that of the original somatic cells. Similarly, this technique allows a distinction to be made between partially and fully reprogrammed cells. We conclude that infrared microspectroscopy signature is a novel methodology to evaluate induced pluripotency and can be added to the tests currently used for this purpose.

Biochemical label-free tissue imaging with subcellular-resolution synchrotron FTIR with focal plane array detector

The critical questions into the cause of neural degeneration, in Alzheimer disease and other neurodegenerative disorders, are closely related to the question of why certain neurons survive. Answers require detailed understanding of biochemical changes in single cells. Fourier transform infrared microspectroscopy is an excellent tool for biomolecular imaging in situ, but resolution is limited. The mid-infrared beamline IRENI (InfraRed ENvironmental Imaging) at the Synchrotron Radiation Center, University of Wisconsin-Madison, enables label-free subcellular imaging and biochemical analysis of neurons with an increase of two orders of magnitude in pixel spacing over current systems. With IRENI's capabilities, it is now possible to study changes in individual neurons in situ, and to characterize their surroundings, using only the biochemical signatures of naturally-occurring components in unstained, unfixed tissue. We present examples of analyses of brain from two transgenic mouse models of Alzheimer disease (TgCRND8 and 3xTg) that exhibit different features of pathogenesis. Data processing on spectral features for nuclei reveals individual hippocampal neurons, and neurons located in the proximity of amyloid plaque in TgCRND8 mouse. Elevated lipids are detected surrounding and, for the first time, within the dense core of amyloid plaques, offering support for inflammatory and aggregation roles. Analysis of saturated and unsaturated fatty acid ester content in retina allows characterization of neuronal layers. IRENI images also reveal spatially-resolved data with unprecedented clarity and distinct spectral variation, from sub-regions including photoreceptors, neuronal cell bodies and synapses in sections of mouse retina. Biochemical composition of retinal layers can be used to study changes related to disease processes and dietary modification.

Infrared spectral signatures of CDCP1-induced effects in colon carcinoma cells

Metastasis is the major cause of death by cancer. Indeed, metastatic colonies can reactivate and become life threatening, sometimes months or years after the initial diagnosis and surgery of the primary tumor. Therefore, there is a crucial need to develop methods for diagnosis of tumor cells that exhibit high metastatic potential. Here, we addressed the capability of vibrational spectroscopy for investigating the effects induced by CDCP1 expression in colon carcinoma cells. This transmembrane protein has been suggested to play a key role in metastasis by its pleiotropic function. We focused on a cellular model constituted by the cell lines SW480 and SW620 derived respectively from the primary tumor and a lymph node metastasis of the same patient. Induced CDCP1 expression in SW480 led to marked changes in cell morphology. Whereas SW480 form a cell layer, the SW480/CDCP1 cells exhibited reduced cell-to-cell contact. On collagen I, SW480 was more spread and filopodia were observed. In contrast, SW480/CDCP1 cells exhibited lower spreading with no formation of filopodia. Synchrotron Fourier transform infrared microspectroscopy experiments were performed on this cellular model. High quality spectroscopic information at sub-cellular resolution, provided by the use of the synchrotron source in infrared microspectroscopy, was recorded on numerous individual cells. Multivariate analysis of spectra recorded using principal component analysis indicated a highest intensity increase of the 970 and 1080 cm(-1) bands, and a modest intensity increase of the 1240 cm(-1) band in the SW480/CDCP1 cells. These bands were correlated with an increased content of phosphorylated proteins as confirmed by in situ labelling using a monoclonal antibody directed against phosphorylated tyrosines. Altogether, these results demonstrate that the vibrational technique used in this study exhibits the capability to characterize spectral signatures of CDCP1-induced effects in colon carcinoma cells. This study may open new avenues for rapid diagnosis of cells with a metastatic potential.

Spectroscopic signature of mouse embryonic stem cell-derived hepatocytes using synchrotron Fourier transform infrared microspectroscopy

Stem cell-based therapy for liver regeneration has been proposed to overcome the persistent shortage in the supply of suitable donor organs. A requirement for this to succeed is to find a rapid method to detect functional hepatocytes, differentiated from embryonic stem cells. We propose Fourier transform infrared (FTIR) microspectroscopy as a versatile method to identify the early and last stages of the differentiation process leading to the formation of hepatocytes. Using synchrotron-FTIR microspectroscopy, the means of identifying hepatocytes at the single-cell level is possible and explored. Principal component analysis and subsequent partial least-squares (PLS) discriminant analysis is applied to distinguish endoderm induction from hepatic progenitor cells and matured hepatocyte-like cells. The data are well modeled by PLS with endoderm induction, hepatic progenitor cells, and mature hepatocyte-like cells able to be discriminated with very high sensitivity and specificity. This method provides a practical tool to monitor endoderm induction and has the potential to be applied for quality control of cell differentiation leading to hepatocyte formation.

Calcifications in human osteoarthritic articular cartilage: ex vivo assessment of calcium compounds using XANES spectroscopy

Calcium (Ca(2+))-containing crystals (CCs), including basic Ca(2+) phosphate (BCP) and Ca(2+) pyrophosphate dihydrate (CPPD) crystals, are associated with severe forms of osteoarthritis (OA). Growing evidence supports a role for abnormal articular cartilage mineralization in the pathogenesis of OA. However, the role of Ca(2+) compounds in this mineralization process remains poorly understood. Six patients, who underwent total knee joint replacement for primary OA, have been considered in this study. Cartilage from femoral condyles and tibial plateaus in the medial and lateral compartments was collected as 1 mm-thick slices cut tangentially to the articular surface. First, CCs presence and biochemical composition were assessed using Fourier transform infrared spectroscopy (FT-IR). Next, Ca(2+) compound biochemical form was further assessed using X-ray absorption spectroscopy (XAS) performed at the Ca(2+) K-absorption edge. Overall, 12 cartilage samples were assessed. Using FT-IR, BCP and CPPD crystals were detected in four and three out of 12 samples, respectively. Ca(2+) compound biochemical forms differed between areas with versus without CCs, when compared using XAS. The complete set of data shows that XANES spectroscopy can be used to accurately characterize sparse CCs in human OA cartilage. It is found that Ca(2+) compounds differ between calcified and non-calcified cartilage areas. In calcified areas they appear to be mainly involved in calcifications, namely Ca(2+) crystals.

Vibrational spectroscopy differentiates between multipotent and pluripotent stem cells

Over the last few years, there has been an increased interest in the study of stem cells in biomedicine for therapeutic use and as a source for healing diseased or injured organs/tissues. More recently, vibrational spectroscopy has been applied to study stem cell differentiation. In this study, we have used both synchrotron based FTIR and Raman microspectroscopies to assess possible differences between human pluripotent (embryonic) and multipotent (adult mesenchymal) stem cells, and how O(2) concentration in cell culture could affect the spectral signatures of these cells. Our work shows that infrared spectroscopy of embryonic (pluripotent) and adult mesenchymal (multipotent) stem cells have different spectral signatures based on the amount of lipids in their cytoplasm (confirmed with cytological staining). Furthermore, O(2) concentration in cell culture causes changes in both the FTIR and Raman spectra of embryonic stem cells. These results show that embryonic stem cells might be more sensitive to O(2) concentration when compared to mesenchymal stem cells. While vibrational spectroscopy could therefore be of potential use in identifying different populations of stem cells further work is required to better understand these differences.

Synchrotron IR spectromicroscopy: chemistry of living cells

Advanced analytical capabilities of synchrotron IR spectromicroscopy meet the demands of modern biological research for studying molecular reactions in individual living cells. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.).

Multimodal spectroscopy combining time-of-flight-secondary ion mass spectrometry, synchrotron-FT-IR, and synchrotron-UV microspectroscopies on the same tissue section

Mass spectrometry and spectroscopy-based approaches can provide an overview of the chemical composition of a tissue sample. This opens up the possibility to investigate in depth the subtle biochemical changes associated with pathological tissues. In this study, time-of-flight secondary ion mass spectrometry (TOF-SIMS) and synchrotron-FT-IR and -UV imaging were applied to the same tissue section by using the same sample holder. The tested sample involved liver cirrhosis, which is characterized by regeneration nodules surrounded by annular fibrosis. A tissue section from a cirrhotic liver was deposited on a gold coated glass slide and was initially analyzed by FT-IR microspectroscopy in order to image the distribution of lipids, proteins, sugars, and nucleic acids. This technique has identified collagen enrichment in fibrosis whereas esters were mostly distributed into the cirrhotic nodules. The exact same section was investigated using TOF-SIMS demonstrating that some molecular lipid species were differentially distributed into the fibrosis areas or cirrhotic nodules. Spectra of UV microspectroscopy obtained from the same section allowed visualizing high autofluorescence from fibrous septa confirming the presence of collagen. Altogether, these results demonstrated that TOF-SIMS and FT-IR/UV microspectroscopy analyses can be successfully performed on the same tissue section.

Synchrotron-based FTIR spectra of stained single cells. Towards a clinical application in pathology

Over the last few years, FTIR spectroscopy has become a potential analytical method in tissue and cell studies for cancer diagnosis. This has opened a way towards clinical applications such as a tool that would scan samples to assess the presence or absence of malignant cells in biopsies, or as an aid to help pathologists to better characterise those cells that are suspicious but not diagnostic for cancer. The latter application has the problem that in order to assess these cells pathologists would have already dealt with stained samples. Therefore, it is important to understand how staining would affect the spectra of cells. To this purpose, we have conducted this study in order to clarify, first, how haematoxylin and eosin (H&E) and Papanicolau (Pap) stainings affect the spectra of single cells and, second, whether FTIR spectroscopy could differentiate between stained lung cancer cells and their normal counterparts. Furthermore, different cell preparations (cytospin, and smear) used in cytological diagnosis were assessed. Experiments performed using a bright infrared (IR) source (synchrotron) showed that both H&E and Pap staining induced marked changes in the lipid and amide-II band regions. Despite this, FTIR spectroscopy of already stained cells is capable of differentiating between lung cancer cells and their normal counterparts. The clinical applications of this methodology are discussed.

Facing the challenge of biosample imaging by FTIR with a synchrotron radiation source

Fourier-transform infrared (FTIR) synchrotron radiation (SR) microspectroscopy is a powerful molecular probe of biological samples at cellular resolution (<10 microm). As the brilliance of SR is 100-1000 times higher than that of a conventional Globar source, FTIR microscopes are now available in almost all advanced SR facilities around the world. However, in spite of this superior performance, the expected advances in IR SR microscopy have not yet been realised, particularly with regard to bio-analytical studies of single cells and soft tissues. In recent decades solid-state array detectors have revolutionized the fields of molecular spectroscopy and chemical imaging, and now new IR focal plane array detectors implemented at ultra-bright SR facilities will extend the performance and overcome the existing limitations, possibly allowing IR SR instrumentation to achieve the highest sensitivity and resolution of molecular imaging. The impact of IR imaging on large tissue area and the complexity of the analysis are discussed. In view of the high brilliance of SR sources, a comparison of published microscope images is given. Finally, it is briefly outlined how an optimized combination of IR instrumentation and SR optical systems could reach the expected advantages of a SR-based FTIR imaging system.

Label-free biochemical characterization of stem cells using vibrational spectroscopy

Raman and infrared (IR) spectroscopy are two complementary vibrational spectroscopic techniques that have experienced a tremendous growth in their use in biological and biomedical research. This is, in large part, due to their unique capability of providing label-free intrinsic chemical information of living biological samples at tissue, cellular, or sub-cellular resolutions. This article reviews recent developments in applying these techniques for the characterization of stem cells. A discussion of the potential for these methods to address some of the major challenges in stem cell research is presented, as well as the technological and scientific advancements that are needed to progress the knowledge in the field.

Chemical imaging on liver steatosis using synchrotron infrared and ToF-SIMS microspectroscopies

Fatty liver or steatosis is a frequent histopathological change. It is a precursor for steatohepatitis that may progress to cirrhosis and in some cases to hepatocellular carcinoma. In this study we addressed the in situ composition and distribution of biochemical compounds on tissue sections of steatotic liver using both synchrotron FTIR (Fourier transform infrared) and ToF-SIMS (time of flight secondary ion mass spectrometry) microspectroscopies. FTIR is a vibrational spectroscopy that allows investigating the global biochemical composition and ToF-SIMS lead to identify molecular species in particular lipids. Synchrotron FTIR microspectroscopy demonstrated that bands linked to lipid contribution such as -CH₃ and -CH₂ as well as esters were highly intense in steatotic vesicles. Moreover, a careful analysis of the -CH₂ symmetric and anti-symmetric stretching modes revealed a slight downward shift in spectra recorded inside steatotic vesicles when compared to spectra recorded outside, suggesting a different lipid environment inside the steatotic vesicles. ToF-SIMS analysis of such steatotic vesicles disclosed a selective enrichment in cholesterol as well as in diacylglycerol (DAG) species carrying long alkyl chains. Indeed, DAG C36 species were selectively localized inside the steatotic vesicles whereas DAG C30 species were detected mostly outside. Furthermore, FTIR detected a signal corresponding to olefin (C = C, 3000-3060 cm⁻¹) and revealed a selective localization of unsaturated lipids inside the steatotic vesicles. ToF-SIMS analysis definitely demonstrated that DAG species C30, C32, C34 and C36 carrying at least one unsaturated alkyl chain were selectively concentrated into the steatotic vesicles. On the other hand, investigations performed on the non-steatotic part of the fatty livers have revealed important changes when compared to the normal liver. Although the non-steatotic regions of fatty livers exhibited normal histological aspect, IR spectra demonstrated an increase in the lipid content and ToF-SIMS detected small lipid droplets corresponding most likely to the first steps of lipid accretion.

IR spectroscopy reveals effect of non-cytotoxic doses of anti-tumour drug on cancer cells

Identifying early cellular events in response to a chemotherapy drug treatment, in particular at low doses that will destroy the highest possible number of cancer cells, is an important issue in patient management. In this study, we employed Fourier transform infrared spectroscopy as a potential tool to access such information. We used as model the non-small cell lung cancer cell line, Calu-1. They were exposed to cytostatic doses (0.1 to 100 nM for 24, 48 and 72 h) of gemcitabine, an anti-tumour drug, currently used in treatment of lung cancer patients. In these conditions, inhibition of cell proliferation ranges from weak (< or = 5%), to moderate (approximately 23%), to high (82-95%) without affecting cell viability. Following drug treatment as a function of doses and incubation times, the spectra of cell populations and of individual cells were acquired using a bench-top IR source and a synchrotron infrared microscope. It is demonstrated that spectral cell response to gemcitabine is detectable at sublethal doses and that effects observed on cell populations are similar to those from single cells. Using cluster analysis, spectra could be classified in two main groups: a first group that contains spectra of cells exhibiting a weak or moderate proliferation rate and a second group with spectra from cells presenting a high growth inhibition. These results are promising since they show that effects of subtoxic doses can also be monitored at the single-cell level with the clinical implications that this may have in terms of patient benefit and response to chemotherapy.

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.

Identification of monoclinic calcium pyrophosphate dihydrate and hydroxyapatite in human sclera using Raman microspectroscopy

Raman microspectroscopy was first used to determine the composition of a calcified plaque located at the pterygium-excision site of a 51-year-old female patient's left nasal sclera after surgery. It was unexpectedly found that the Raman spectrum of the calcified sample at 1149, 1108, 1049, 756, 517, 376 and 352/cm was similar to the Raman spectrum of monoclinic form of calcium pyrophosphate dihydrate (CPPD) crystal, but differed from the Raman spectrum of triclinic form of CPPD. An additional peak at 958/cm was also observed in the Raman spectrum of the calcified plaque, which was identical to the characteristic peak at 958/cm of hydroxyapatite (HA). This is the first study to report the spectral biodiagnosis of both monoclinic CPPD and HA co-deposited in the calcified plaque of a patient with sclera dystrophic calcification using Raman microspectroscopy.