Highlighting the hygroscopic capacities of apiogalacturonans.

To meet the needs of dehydrated skin, molecules with a high hygroscopic potential are necessary to hydrate it effectively and durably. In this context, we were interested in pectins, and more precisely in apiogalacturonans (AGA), a singular one that is currently only found in a few species of aquatic plants. As key structures in water regulation of these aquatic plants and thanks to their molecular composition and conformations, we hypothesized that they could have beneficial role for skin hydration. Spirodela polyrhiza is a duckweed known to be naturally rich in AGA. The aim of this study was to investigate the hygroscopic potential of AGA. Firstly, AGA models were built based on structural information obtained from previous experimental studies. Molecular dynamics (MD) simulations were performed, and the hygroscopic potential was predicted in silico by analyzing the frequency of interaction of water molecules with each AGA residue. Quantification of interactions identified the presence of 23 water molecules on average in contact with each residue of AGA. Secondly, the hygroscopic properties were investigated directly in vivo. Indeed, the water capture in the skin was measured in vivo by Raman microspectroscopy thanks to the deuterated water (D20) tracking. Investigations revealed that AGA significantly capture and retain more water in the epidermis and deeper than a placebo control. Not only do these original natural molecules interact with water molecules, but they capture and retain them efficiently in the skin.

New approach for hair keratin characterization: Use of the confocal Raman spectroscopy to assess the effect of thermal stress on human hair fibre.

OBJECTIVE: The objective of our research was to investigate the heat-protecting effect of a product ex vivo and in vivo on human hair fibres. METHODS: A preparatory study was carried out in order to determine an optimal threshold of thermal stress. For this, the structure of cross-sections of the hair fibre was observed by optical microscopy. Then, Scanning Electron Microscopy (SEM) and Confocal Raman Spectroscopy (CRS) were applied to analyse ex vivo and in vivo morphological and molecular damage in hair structure after heat stress. Finally, in vivo tests were used to collect consumer perception. RESULTS: The preparatory study enabled us to determine an optimal stress threshold of 10 heating cycle for SEM and 5 heating cycle for CRS. Based on spectral hierarchical classification using Ward's clustering algorithm, the ex vivo Raman results show that the spectral signature of the hair treated and heated is very close to the negative control. This shows that the product preserves the keratin structure after thermal stress. These results were also confirmed by an in vivo Raman analysis performed on hair samples from 5 donors. In concordance with Raman results, SEM shows that treated hair presents lesser "bubbles" and "crackling" on the hair surface. Finally, the in vivo studies proved that hair was more protected from heat. CONCLUSION: The authors concluded that the product shows protective properties with respect to morphological and molecular heat damage. We also demonstrate that the product promotes the α-helix keratin conformation and preserves the S-S disulfide bands.

OBJECTIF: L'objectif de notre étude est d'évaluer ex vivo et in vivo l'effet thermoprotecteur d'un produit sur les fibres capillaires humaines. MÉTHODES: Une étude préparatoire a été réalisée afin de déterminer un seuil optimal du stress thermique. Pour cela, la structure des coupes transversales des cheveux a été observée par microscopie optique. Ensuite, la microscopie électronique à balayage (MEB) et la spectroscopie confocale Raman (SCR) ont été appliquées pour analyser les dommages morphologiques et moléculaires (ex vivo et in vivo) de la structure du cheveu après un stress thermique. Enfin, des tests in vivo ont été réalisés pour recueillir la perception des consommateurs. RÉSULTATS: L'étude préparatoire nous a permis de déterminer un seuil de stress thermique optimal correspondant à 10 cycles de chauffage pour la MEB et 5 cycles de chauffage pour la SCR. Basés sur une classification hiérarchique utilisant l'algorithme de Ward, les résultats Raman « ex vivo ¼ montrent que la signature spectrale des cheveux traités et chauffés est très proche du témoin négatif. Cela montre que le produit préserve la structure de la kératine après un stress thermique. Ces résultats ont également été confirmés par une analyse Raman « in vivo ¼ réalisée sur des échantillons de cheveux de 5 donneurs. En concordance avec les résultats Raman, la MEB montre que les cheveux traités présentent moins de « bulles ¼ et de « craquelures ¼ à la surface des cheveux. Enfin, l'étude in vivo a prouvé que les cheveux sont mieux protégés de la chaleur. CONCLUSION: Les auteurs ont conclu que le produit présente des propriétés protectrices vis-à-vis des dommages thermiques morphologiques et moléculaires. Nous avons démontré également que le produit favorise la conformation de la kératine en hélice-α et préserve les bandes disulfures S-S.

Combining Raman imaging and MCR-ALS analysis for monitoring retinol permeation in human skin.

BACKGROUND: Monitoring the transcutaneous permeation of exogenous molecules using conventional techniques generally requires long pre-analytical preparation or labelling of samples. However, Raman spectroscopy is a label-free and non-destructive method which provides spatial distribution of tracked actives in skin. The aim of our study was to prove the interest of Raman imaging coupled with multivariate curve resolution alternating least square (MCR-ALS) analysis in monitoring retinol penetration into frozen and living human skin. MATERIALS AND METHODS: After topical treatment of skin samples by free or encapsulated retinol, thin cross sections were analysed by Raman imaging (up to 100 µm depth). Mann-Whitney test was used to identify retinol spectroscopic markers in skin. MCR-ALS was used to estimate retinol contribution in Raman spectral images. Heat maps were constructed to compare the distribution of free and encapsulated retinol in skin models. RESULTS: We identified the bands at 1158, 1196 and 1591 cm-1 as specific features for monitoring retinol in skin. Moreover, our MCR-ALS results showed an improvement of retinol penetration (up to 30 µm depth) with the encapsulated form as well as storage reservoir formation in stratum corneum, for each skin model. Finally, greater retinol penetration into living skin was observed. CONCLUSION: This study shows a proof of concept for the evaluation of retinol penetration in skin using Raman imaging coupled with MCR-ALS. This concept needs to be validated on more subjects to include inter-individual variability but also other factors affecting skin permeation (age, sex, pH, etc). Our study can be extended to other actives.

Investigation of the molecular signature of greying hair shafts.

OBJECTIVE: Hair greying (i.e. canitie) is a physiological process occurring with the loss of melanin production and deposition within the hair shafts. Many studies reported the oxidation as the main biological process underlying this defect of pigmentation. Even though the overall appearance and biomechanical properties of hairs are reported to be altered with greying, there is a lack of information about molecular modifications occurring in grey hair shafts. The aim of this study was thus to investigate the molecular signature and associated changes occurring in greying hair shafts by confocal Raman microspectroscopy. METHODS: This study was conducted on pigmented, intermediate (i.e. grey) and unpigmented hairs taken from 29 volunteers. Confocal Raman microspectroscopy measurements were acquired directly on hair shafts. RESULTS: Automatic classification of Raman spectra revealed 5 groups displaying significant differences. Hence, the analysis of the molecular signature highlighted the existence of 3 sub-groups within grey hair: light, medium and dark intermediate. Among molecular markers altered in the course of greying, this study identified for the first time a gradual modification of lipid conformation (trans/gauche ratio) and protein secondary structure (α-helix/ß-sheet ratio), referring respectively to an alteration of barrier function and biomechanical properties of greying hair. CONCLUSION: This study thus reports for the first time a highly specific molecular signature as well as molecular modifications within grey hair shaft.

OBJECTIF: Le grisonnement du cheveu (i.e. canitie) est un processus physiologique correspondant à l'altération de la production et du dépôt des pigments de mélanine au sein de la tige pilaire. De nombreuses études identifient l'oxydation en tant que principal phénomène à l'origine de ce défaut de pigmentation. L'apparence globale et les propriétés biomécaniques des cheveux grisonnants sont également rapportées comme étant altérées. Cependant, il existe un manque d'information concernant les modifications moléculaires ayant lieu dans la tige pilaire grisonnante. Le but de cette étude était donc d'investiguer par microspectroscopie confocale Raman la signature moléculaire de la tige pilaire grisonnante ainsi que les changements biologiques associés. MÉTHODES: Cette étude a été réalisée sur des cheveux pigmentés, intermédiaires (i.e. gris) et non pigmentés, prélevés sur 29 volontaires. Les mesures par microspectroscopie Raman confocale ont directement été acquises sur la tige pilaire. RÉSULTATS: Une classification automatique des spectres Raman a permis de révéler 5 groupes présentant des différences significatives. Ainsi, l'analyse de la signature moléculaire spectrale identifie 3 sous-groupes au sein des cheveux gris : intermédiaires clairs, moyens et foncés. Parmi les marqueurs moléculaires altérés au cours du grisonnement, cette étude identifie pour la première fois une modification graduelle de la conformation des lipides (ratio trans /gauche) et de la structure secondaire des protéines (ratio hélice α/feuillets ß). Ces marqueurs correspondent respectivement à l'altération de la fonction barrière et des propriétés biomécaniques des cheveux gris. CONCLUSION: Cette étude met en évidence pour la première fois une signature moléculaire extrêmement précise ainsi que des modifications moléculaires en lien avec le grisonnement de la tige pilaire.

Correction: Confocal Raman microspectroscopy for skin characterization: a comparative study between human skin and pig skin.

Correction for 'Confocal Raman microspectroscopy for skin characterization: a comparative study between human skin and pig skin' by Sana Tfaili et al., Analyst, 2012, 137, 3673-3682, DOI: .

Mid-infrared spectral microimaging of inflammatory skin lesions.

Skin is one of the most important organs of the human body because of its characteristics and functions. There are many alterations, either pathological or physiological, that can disturb its functioning. However, at present all methods used to investigate skin diseases, non-invasive or invasive, are based on clinical examinations by physicians. Thus, diagnosis, prognosis and therapeutic management rely on the expertise of the practitioner, the quality of the method and the accessibility of distinctive morphological characteristics of each lesion. To overcome the high sensitivity of these parameters, techniques based on more objective criteria must be explored. Vibrational spectroscopy has become as a key technique for tissue analysis in the biomedical research field. Based on a non-destructive light/matter interaction, this tool provides information about specific molecular structure and composition of the analyzed sample, thus relating to its precise physiopathological state and permitting to distinguish lesional from normal tissues. This label-free optical method can be performed directly on the paraffin-embedded tissue sections without chemical dewaxing. In this study, the potential of the infrared microspectroscopy, combined with data classification methods was demonstrated, to characterize at the tissular level different types of inflammatory skin lesions, and this independently from conventional histopathology.

Atopic skin: In vivo Raman identification of global molecular signature, a comparative study with healthy skin.

Atopic dermatitis (AD) is the most common skin inflammatory disease, affecting up to 3% of adults and 20% of children. Skin barrier impairment is thought to be the primary factor in this disease. Currently, there is no method proposed to monitor non-invasively the different molecular disorders involved in the upper layer of AD skin. Raman microspectroscopy has proved to be a powerful tool to characterize some AD molecular descriptors such as lipid content, global hydration level, filaggrin and its derivatives. Our investigations aimed to extend the use of in vivo Raman microspectroscopy as a rapid and non-invasive diagnostic technique for lipid conformation and organization, protein secondary structure and bound water content analysis in atopic skin. Our approach was based on the analysis of Raman data collected on the stratum corneum (SC) of 11 healthy and 10 mild-to-moderate atopic patients. Atopic skin revealed a modification of lipid organization and conformation in addition to the decrease of the lipid-to-protein ratio. This study also highlighted a reduction of the bound water and an increase in protein organized secondary structure in atopic skin. All these descriptors worsen the barrier function, state and appearance of the skin in AD. This precise and relevant information will allow an in vivo follow-up of the pathology and a better evaluation of the pharmacological activity of therapeutic molecules for the treatment of AD.

Doxorubicin Drug-Eluting Embolic Chemoembolization of Hepatocellular Carcinoma: Study of Midterm Doxorubicin Delivery in Resected Liver Specimens.

This study evaluated the midterm delivery of doxorubicin in liver specimens from patients (N = 4) with hepatocellular carcinoma treated with drug-eluting embolic (DEE) transarterial chemoembolization. The patients had surgical resection 57, 79, 80 and 105 days after doxorubicin DEE chemoembolization. Doxorubicin concentrations inside embolic particles and in surrounding tissues were assessed by infrared microspectroscopy and microspectrofluorimetry, respectively. Embolic particles still contained doxorubicin and provided sustained drug delivery within targeted tissues 80 days after chemoembolization. Doxorubicin was undetectable after 105 days. In addition, aggregation of embolic particles inside vessel lumina was associated with slower doxorubicin elution and higher tissue concentrations when the number of aggregated embolic particles increased.

Digital de-waxing on FTIR images.

This paper presents a procedure that digitally neutralizes the contribution of paraffin to FTIR hyperspectral images. A brief mathematical derivation of the procedure is demonstrated and applied on one normal human colon sample to exemplify the de-waxing procedure. The proposed method includes construction of a paraffin model based on PCA, EMSC normalization and application of two techniques for spectral quality control. We discuss every step in which the researcher needs to take a subjective decision during the de-waxing procedure, and we explain how to make an adequate choice of parameters involved. Application of this procedure to 71 hyperspectral images collected from 55 human colon biopsies (20 normal, 17 ulcerative colitis, and 18 adenocarcinoma) showed that paraffin was appropriately neutralized, which made the de-waxed images adequate for analysis by pattern-recognition techniques such as k-means clustering or PCA-LDA.

Vibrational Analysis of Lung Tumor Cell Lines: Implementation of an Invasiveness Scale Based on the Cell Infrared Signatures.

Assessing the tumor invasiveness is a paramount diagnostic step to improve the patients care. Infrared spectroscopy access the chemical composition of samples; and in combination with statistical multivariate processing, presents the capacity to highlight subtle molecular alterations associated with malignancy development. Our investigation demonstrated that infrared signatures of cell lines presenting various invasiveness phenotypes contain discriminant spectral features, which are useful informative signals to implement an objective invasiveness scale. This last development reflects the interest of vibrational approach as a candidate biophotonic label-free technique, usable in routine clinics, to characterize quantitatively tumor aggressiveness. In addition, the methodology can reveal the heterogeneity of cancer cells, opening the way to further researches in cancer science.

Highlighting the impact of aging on type I collagen: label-free investigation using confocal reflectance microscopy and diffuse reflectance spectroscopy in 3D matrix model.

During aging, alterations of extracellular matrix proteins contribute to various pathological phenotypes. Among these alterations, type I collagen cross-linking and associated glycation products accumulation over time detrimentally affects its physico-chemical properties, leading to alterations of tissue biomechanical stability. Here, different-age collagen 3D matrices using non-destructive and label-free biophotonic techniques were analysed to highlight the impact of collagen I aging on 3D constructs, at macroscopic and microscopic levels. Matrices were prepared with collagens extracted from tail tendons of rats (newborns, young and old adults) to be within the physiological aging process. The data of diffuse reflectance spectroscopy reveal that aging leads to an inhibition of fibril assembly and a resulting decrease of gel density. Investigations by confocal reflectance microscopy highlight poor-fibrillar structures in oldest collagen networks most likely related to the glycation products accumulation. Complementarily, an infrared analysis brings out marked spectral variations in the Amide I profile, specific of the peptidic bond conformation and for carbohydrates vibrations as function of collagen-age. Interestingly, we also highlight an unexpected behavior for newborn collagen, exhibiting poorly-organized networks and microscopic features close to the oldest collagen. These results demonstrate that changes in collagen optical properties are relevant for investigating the incidence of aging in 3D matrix models.

In vivo confocal Raman microspectroscopy of the human skin: highlighting of spectral markers associated to aging via a research of correlation between Raman and biometric mechanical measurements.

Skin plays a protective role against the loss of water and external aggression, including mechanical stresses. These crucial functions are ensured by different cutaneous layers, particularly the stratum corneum (SC). During aging, the human skin reveals some apparent modifications of functionalities such as a loss of elasticity. Our investigations aimed at demonstrating that Raman microspectroscopy, as a label-free technique with a high molecular specificity, is efficient to assess in vivo the molecular composition of the skin and the alterations underwent during aging. Our approach was based on a search for correlation between Raman data collected on healthy female volunteers of different ages (from 21 to 70 years old) by means of a remote confocal Raman and skin firmness measurements used as a reference method. Raman and biometric data were then submitted to a partial least square (PLS)-based data processing. Our experiments demonstrated the potential of Raman microspectroscopy to provide an objective in vivo assessment of the skin "biological age" that can be very different from the "chronological age" of the person. In addition, Raman features sensitive to the elasticity and the fatigability of the SC were highlighted. Thereafter, calibration transfer functions were constructed to show the possibility to compare the results obtained during two distinct measurement campaigns conducted with two Raman probes of the same conception. This approach could lead to several interesting prospects, in particular by objectifying the effects of dermocosmetic products on the superficial layers of the skin and by accessing some underlying molecular mechanisms.

Investigating the relationship between changes in collagen fiber orientation during skin aging and collagen/water interactions by polarized-FTIR microimaging.

Upon chronological aging, human skin undergoes structural and molecular modifications, especially at the level of type I collagen. This macromolecule is one of the main dermal structural proteins and presents several age-related alterations. It exhibits a triple helical structure and assembles itself to form fibrils and fibers. In addition, water plays an important role in stabilizing the collagen triple helix by forming hydrogen-bonds between collagen residues. However, the influence of water on changes of dermal collagen fiber orientation with age has not been yet understood. Polarized-Fourier Transform Infrared (P-FTIR) imaging is an interesting biophotonic approach to determine in situ the orientation of type I collagen fibers, as we have recently shown by comparing skin samples of different ages. In this work, P-FTIR spectral imaging was performed on skin samples from two age groups (35- and 38-year-old on the one hand, 60- and 66-year-old on the other hand), and our analyses were focused on the effect of H2O/D2O substitution. Spectral data were processed with fuzzy C-means (FCM) clustering in order to distinguish different orientations of collagen fibers. We demonstrated that the orientation was altered with aging, and that D2O treatment, affecting primarily highly bound water molecules, is more marked for the youngest skin samples. Collagen-bound water-related spectral markers were also highlighted. Our results suggest a weakening of water/collagen interactions with age. This non-destructive and label-free methodology allows us to understand better the importance of bound water in collagen fiber orientation alterations occurring with skin aging. Obtaining such structural information could find benefits in dermatology as well as in cosmetics.

Automated Quantification of Tumor Viability in a Rabbit Liver Tumor Model after Chemoembolization Using Infrared Imaging.

The rabbit VX2 tumor is a fast-growing carcinoma model commonly used to study new therapeutic devices, such as catheter-based therapies for patients with inoperable hepatocellular carcinoma. The evaluation of tumor viability after such locoregional therapies is essential to directing hepatocellular carcinoma management. We used infrared microspectroscopy for the automatic characterization and quantification of the VX2 liver tumor viability after drug-eluting beads transarterial chemoembolization (DEB-TACE). The protocol consisted of K-means clustering followed by principal component analysis (PCA) and linear discriminant analysis (LDA). The K-means clustering was used to classify the spectra from the infrared images of control or treated tumors and to build a database of many tissue spectra. On the basis of this reference library, the PCA-LDA analysis was used to build a predictive model to identify and quantify automatically tumor viability on unknown tissue sections. For the DEB group, the LDA model determined that the surface of tumor necrosis represented 91.6% ± 8.9% (control group: 33.1% ± 19.6%; Mann-Whitney P = 0.0004) and the viable tumor 2.6% ± 4% (control group: 62.2% ± 15.2%; Mann-Whitney P = 0.0004). Tissue quantification measurements correlated well with tumor necrosis (r = 0.827, P < 0.0001) and viable tumor (r = 0.840, P < 0.0001). Infrared imaging and PCA-LDA analysis could be helpful for easily assessing tumor viability.

Diagnosis approach of chronic lymphocytic leukemia on unstained blood smears using Raman microspectroscopy and supervised classification.

We have investigated the potential of Raman microspectroscopy combined with supervised classification algorithms to diagnose a blood lymphoproliferative disease, namely chronic lymphocytic leukemia (CLL). This study was conducted directly on human blood smears (27 volunteers and 49 CLL patients) spread on standard glass slides according to a cytological protocol before the staining step. Visible excitation at 532 nm was chosen, instead of near infrared, in order to minimize the glass contribution in the Raman spectra. After Raman measurements, blood smears were stained using the May-Grünwald Giemsa procedure to correlate spectroscopic data classifications with cytological analysis. A first prediction model was built using support vector machines to discriminate between the two main leukocyte subpopulations (lymphocytes and polymorphonuclears) with sensitivity and specificity over 98.5%. The spectral differences between these two classes were associated to higher nucleic acid content in lymphocytes compared to polymorphonuclears. Then, we developed a classification model to discriminate between neoplastic and healthy lymphocyte spectra, with a mean sensitivity and specificity of 88% and 91% respectively. The main molecular differences between healthy and CLL cells were associated with DNA and protein changes. These spectroscopic markers could lead, in the future, to the development of a helpful medical tool for CLL diagnosis.

The relationship between water loss, mechanical stress, and molecular structure of human stratum corneum ex vivo.

Proper hydration of the stratum corneum (SC) is important for maintaining skin's vital functions. Water loss causes development of drying stresses, which can be perceived as 'tightness', and plays an important role in dry skin damage processes. However, molecular structure modifications arising from water loss and the subsequent development of stress has not been established. We investigated the drying stress mechanism by studying, ex vivo, the behaviors of the SC components during water desorption from initially fully hydrated samples using Raman spectroscopy. Simultaneously, we measure the SC mechanical stress with a substrate curvature instrument. Very good correlations of water loss to the mechanical stress of the stratum corneum were obtained, and the latter was found to depend mainly on the unbound water fraction. In addition to that, the water loss is accompanied with an increase of lipids matrix compactness characterized by lower chain freedom, while protein structure showed an increase in amount of α-helices, a decline in α-sheets, and an increase in folding in the tertiary structure of keratin. The drying process of SC involves a complex interplay of water binding, molecular modifications, and mechanical stress. This article provides a better understanding of the molecular mechanism associated to SC mechanics.

Infrared spectral histopathology for cancer diagnosis: a novel approach for automated pattern recognition of colon adenocarcinoma.

Histopathology remains the gold standard method for colon cancer diagnosis. Novel complementary approaches for molecular level diagnosis of the disease are need of the hour. Infrared (IR) imaging could be a promising candidate method as it probes the intrinsic chemical bonds present in a tissue, and provides a "spectral fingerprint" of the biochemical composition. To this end, IR spectral histopathology, which combines IR imaging and data processing techniques, was employed on seventy seven paraffinized colon tissue samples (48 tumoral and 29 non-tumoral) in the form of tissue arrays. To avoid chemical deparaffinization, a digital neutralization of the spectral interference of paraffin was implemented. Clustering analysis was used to partition the spectra and construct pseudo-colored images, for assigning spectral clusters to various tissue structures (normal epithelium, malignant epithelium, connective tissue etc.). Based on the clustering results, linear discriminant analysis was then used to construct a stringent prediction model which was applied on samples without a priori histopathological information. The predicted spectral images not only revealed common features representative of the colonic tissue biochemical make-up, but also highlighted additional features like tumor budding and tumor-stroma association in a label-free manner. This novel approach of IR spectral imaging on paraffinized tissues showed 100% sensitivity and allowed detection and differentiation of normal and malignant colonic features based purely on their intrinsic biochemical features. This non-destructive methodology combined with multivariate statistical image analysis appears as a promising tool for colon cancer diagnosis and opens up the way to the concept of numerical spectral histopathology.

Raman spectroscopy: in vivo quick response code of skin physiological status.

Dermatologists need to combine different clinically relevant characteristics for a better understanding of skin health. These characteristics are usually measured by different techniques, and some of them are highly time consuming. Therefore, a predicting model based on Raman spectroscopy and partial least square (PLS) regression was developed as a rapid multiparametric method. The Raman spectra collected from the five uppermost micrometers of 11 healthy volunteers were fitted to different skin characteristics measured by independent appropriate methods (transepidermal water loss, hydration, pH, relative amount of ceramides, fatty acids, and cholesterol). For each parameter, the obtained PLS model presented correlation coefficients higher than R2=0.9. This model enables us to obtain all the aforementioned parameters directly from the unique Raman signature. In addition to that, in-depth Raman analyses down to 20 µm showed different balances between partially bound water and unbound water with depth. In parallel, the increase of depth was followed by an unfolding process of the proteins. The combinations of all these information led to a multiparametric investigation, which better characterizes the skin status. Raman signal can thus be used as a quick response code (QR code). This could help dermatologic diagnosis of physiological variations and presents a possible extension to pathological characterization.

Changes of skin collagen orientation associated with chronological aging as probed by polarized-FTIR micro-imaging.

During chronological skin aging, alterations in dermal structural proteins cause morphological modifications. Modifications are probably due to collagen fiber (type I collagen) rearrangement and reorientation with aging that have not been researched until now. FTIR microspectroscopy appears as an interesting method to study protein structure under normal and pathological conditions. Associated with a polarizer, this vibrational technique permits us to probe collagen orientation within skin tissue sections, by computing the ratio of integrated intensities of amide I and amide II bands. In this study, we used the polarized-FTIR imaging to evaluate molecular modifications of dermal collagen during chronological aging. The data processing of polarized infrared data revealed that type I collagen fibers become parallel to the skin surface in aged skin dermis. Our approach could find innovative applications in dermatology as well as in cosmetics.

Infrared and Raman imaging for characterizing complex biological materials: a comparative morpho-spectroscopic study of colon tissue.

Complementary diagnostic methods to conventional histopathology are currently being investigated for developing rapid and objective molecular-level understanding of various disorders, especially cancers. Spectral histopathology using vibrational spectroscopic imaging has been put in the frontline as potentially promising in this regard as it provides a "spectral fingerprint" of the biochemical composition of cells and tissues. In order to ascertain the feasible conditions of vibrational spectroscopic methods for tissue-imaging analysis, vibrational multimodal imaging (infrared transmission, infrared-attenuated total reflection, and Raman imaging) of the same colon tissue has been implemented. The spectral images acquired were subjected to multivariate clustering analysis in order to identify on a molecular level the constituent histological organization of the colon tissue such as the epithelium, connective tissue, etc., by comparing the cluster images with the histological reference images. Based on this study, a comparative analysis of important factors involved in the vibrational multimodal imaging approaches such as image resolution, time constraints, their advantages and limitations, and their applicability to biological tissues has been carried out. Out of the three different vibrational imaging modalities tested, infrared-attenuated total reflection mode of imaging appears to provide a good compromise between the tissue histology and the time constraints in achieving similar image contrast to that of Raman imaging at an approximately 33-fold faster measurement time. The present study demonstrates the advantages, the limitations of the important parameters involved in vibrational multimodal imaging approaches, and their potential application toward imaging of biological tissues.