1
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Vieira LG. Overcoming the Contact Problem in Quantitative Attenuated Total Reflection Spectroscopy Analysis of Flat Samples. APPLIED SPECTROSCOPY 2023; 77:1221-1227. [PMID: 37700591 PMCID: PMC10604394 DOI: 10.1177/00037028231199115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2023] [Accepted: 08/16/2023] [Indexed: 09/14/2023]
Abstract
A method for measuring the optical functions of a flat sample made of homogeneous and isotropic material, using attenuated total reflection spectroscopy when there is poor contact between the sample and the internal reflection element is presented. The approach consists in treating the spacing between the internal reflection element and the sample as an adjustable parameter, along with the dispersion model parameters, in the simultaneous fitting of s- and p-polarized spectra obtained when the gap distance is unknown. The method is tested with both synthetic and experimental (polystyrene) spectra. The results demonstrate the method's ability to accurately determine the optical functions even in the presence of a contact problem.
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Affiliation(s)
- Luis G. Vieira
- Centro de Física das Universidades do Minho e do Porto (CF-UM-UP), Laboratório de Física para Materiais e Tecnologias Emergentes (LaPMET) and Departamento de Física, Universidade do Minho, Braga, Portugal
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2
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van Haaren C, De Bock M, Kazarian SG. Advances in ATR-FTIR Spectroscopic Imaging for the Analysis of Tablet Dissolution and Drug Release. Molecules 2023; 28:4705. [PMID: 37375260 DOI: 10.3390/molecules28124705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 06/06/2023] [Accepted: 06/09/2023] [Indexed: 06/29/2023] Open
Abstract
One of the major challenges in the development of effective pharmaceutical formulations for oral administration is the poor solubility of active pharmaceutical ingredients. For this reason, the dissolution process and drug release from solid oral dosage forms, such as tablets, is usually thoroughly studied in order to understand the dissolution behaviour under various conditions and optimize the formulation accordingly. Standard dissolution tests used in the pharmaceutical industry provide information on the amount of drug released over time; however, these do not allow for a detailed analysis of the underlying chemical and physical mechanisms of tablet dissolution. FTIR spectroscopic imaging, by contrast, does offer the ability to study these processes with high spatial and chemical specificity. As such, the method allows us to see the chemical and physical processes which occur inside the tablet as it dissolves. In this review, the power of ATR-FTIR spectroscopic imaging is demonstrated by presenting a number of successful applications of this chemical imaging technique to dissolution and drug release studies for a range of different pharmaceutical formulations and study conditions. Understanding these processes is essential for the development of effective oral dosage forms and optimization of pharmaceutical formulations.
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Affiliation(s)
- Céline van Haaren
- Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK
| | - Marieke De Bock
- Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK
| | - Sergei G Kazarian
- Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK
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3
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Zhang D, Bian Q, Zhou Y, Huang Q, Gao J. The application of label-free imaging technologies in transdermal research for deeper mechanism revealing. Asian J Pharm Sci 2020; 16:265-279. [PMID: 34276818 PMCID: PMC8261078 DOI: 10.1016/j.ajps.2020.07.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Revised: 05/23/2020] [Accepted: 07/06/2020] [Indexed: 12/13/2022] Open
Abstract
The penetration behavior of topical substances in the skin not only relates to the transdermal delivery efficiency but also involves the safety and therapeutic effect of topical products, such as sunscreen and hair growth products. Researchers have tried to illustrate the transdermal process with diversified theories and technologies. Directly observing the distribution of topical substances on skin by characteristic imaging is the most convincing approach. Unfortunately, fluorescence labeling imaging, which is commonly used in biochemical research, is limited for transdermal research for most topical substances with a molecular mass less than 500 Da. Label-free imaging technologies possess the advantages of not requiring any macromolecular dyes, no tissue destruction and an extensive substance detection capability, which has enabled rapid development of such technologies in recent years and their introduction to biological tissue analysis, such as skin samples. Through the specific identification of topical substances and endogenous tissue components, label-free imaging technologies can provide abundant tissue distribution information, enrich theoretical and practical guidance for transdermal drug delivery systems. In this review, we expound the mechanisms and applications of the most popular label-free imaging technologies in transdermal research at present, compare their advantages and disadvantages, and forecast development prospects.
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Affiliation(s)
- Danping Zhang
- Institute of Pharmaceutics, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China
| | - Qiong Bian
- Institute of Pharmaceutics, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China
| | - Yi Zhou
- Institute of Pharmaceutics, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China
| | - Qiaoling Huang
- The Third People's Hospital of Hangzhou, Hangzhou 310012, China
| | - Jianqing Gao
- Institute of Pharmaceutics, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China
- Jiangsu Engineering Research Center for New-Type External and Transdermal Preparations, Changzhou 213000, China
- Corresponding author.
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4
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Song CL, Kazarian SG. Effect of Controlled Humidity and Tissue Hydration on Colon Cancer Diagnostic via FTIR Spectroscopic Imaging. Anal Chem 2020; 92:9691-9698. [DOI: 10.1021/acs.analchem.0c01002] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Cai Li Song
- Department of Chemical Engineering, South Kensington Campus, Imperial College London, London SW7 2AZ, United Kingdom
| | - Sergei G. Kazarian
- Department of Chemical Engineering, South Kensington Campus, Imperial College London, London SW7 2AZ, United Kingdom
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5
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Bhargava R, Madabhushi A. Emerging Themes in Image Informatics and Molecular Analysis for Digital Pathology. Annu Rev Biomed Eng 2017; 18:387-412. [PMID: 27420575 DOI: 10.1146/annurev-bioeng-112415-114722] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Pathology is essential for research in disease and development, as well as for clinical decision making. For more than 100 years, pathology practice has involved analyzing images of stained, thin tissue sections by a trained human using an optical microscope. Technological advances are now driving major changes in this paradigm toward digital pathology (DP). The digital transformation of pathology goes beyond recording, archiving, and retrieving images, providing new computational tools to inform better decision making for precision medicine. First, we discuss some emerging innovations in both computational image analytics and imaging instrumentation in DP. Second, we discuss molecular contrast in pathology. Molecular DP has traditionally been an extension of pathology with molecularly specific dyes. Label-free, spectroscopic images are rapidly emerging as another important information source, and we describe the benefits and potential of this evolution. Third, we describe multimodal DP, which is enabled by computational algorithms and combines the best characteristics of structural and molecular pathology. Finally, we provide examples of application areas in telepathology, education, and precision medicine. We conclude by discussing challenges and emerging opportunities in this area.
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Affiliation(s)
- Rohit Bhargava
- Departments of Bioengineering, Chemical and Biomolecular Engineering, Electrical and Computer Engineering, Mechanical Science and Engineering, and Chemistry, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801;
| | - Anant Madabhushi
- Center for Computational Imaging and Personalized Diagnostics; Departments of Biomedical Engineering, Urology, Pathology, Radiology, Radiation Oncology, General Medical Sciences, Electrical Engineering, and Computer Science; and Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, Ohio 44106;
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6
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Mansour RSH, Sallam AA, Hamdan II, Khalil EA, Yousef I. Elucidation of penetration enhancement mechanism of Emu oil using FTIR microspectroscopy at EMIRA laboratory of SESAME synchrotron. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2017; 185:1-10. [PMID: 28527394 DOI: 10.1016/j.saa.2017.05.026] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2016] [Revised: 05/11/2017] [Accepted: 05/11/2017] [Indexed: 06/07/2023]
Abstract
It has been proposed that Emu oil possesses skin permeation-enhancing effect. This study aimed to address its possible penetration enhancement mechanism(s) using IR microscopy, in accordance with LPP theory. The penetration of Emu oil through the layers of human skin was accomplished by monitoring oil-IR characteristic feature at 3006cm-1. The unsaturated components of Emu oil accumulated at about 270μm depth of skin surface. The interaction of Emu oil with lipid and protein constituents of SC was investigated in comparison with a commonly used enhancer, IPM. Inter-sample spectral differences were identified using PCA and linked with possible enhancement mechanisms. Emu oil treatment caused a change in the slope of the right contour of amide I band of the protein spectral range. This was also clear in the second derivative spectra where the emergence of a new shoulder at higher frequency was evident, suggesting disorganization of keratin α-helix structure. This effect could be a result of disruption of some hydrogen bonds in which amide CO and NH groups of keratin are involved. The low intensity of the emerged shoulder is also in agreement with formation of weaker hydrogen bonds. IPM did not affect the protein component. No conclusions regarding the effect of penetration enhancers on the SC lipids were obtained. This was due to the overlap of the endogenous (skin) and exogenous (oil) CH stretching and scissoring frequencies. The SC carbonyl stretching peak disappeared as a result of IPM treatment which may reflect some degree of lipid extraction.
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Affiliation(s)
| | | | - Imad I Hamdan
- Faculty of Pharmacy, University of Jordan, 11942 Amman, Jordan
| | - Enam A Khalil
- Faculty of Pharmacy, University of Jordan, 11942 Amman, Jordan
| | - Ibraheem Yousef
- SESAME Synchrotron, P.O. Box 7, 19252 Allan, Jordan; ALBA Synchrotron, Carrer de la Llum 2-26, 08290, Cerdanyola del Vallès, Barcelona, Spain.
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7
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Andrew Chan KL, Kazarian SG. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) imaging of tissues and live cells. Chem Soc Rev 2016; 45:1850-64. [PMID: 26488803 DOI: 10.1039/c5cs00515a] [Citation(s) in RCA: 136] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
FTIR spectroscopic imaging is a label-free, non-destructive and chemically specific technique that can be utilised to study a wide range of biomedical applications such as imaging of biopsy tissues, fixed cells and live cells, including cancer cells. In particular, the use of FTIR imaging in attenuated total reflection (ATR) mode has attracted much attention because of the small, but well controlled, depth of penetration and corresponding path length of infrared light into the sample. This has enabled the study of samples containing large amounts of water, as well as achieving an increased spatial resolution provided by the high refractive index of the micro-ATR element. This review is focused on discussing the recent developments in FTIR spectroscopic imaging, particularly in ATR sampling mode, and its applications in the biomedical science field as well as discussing the future opportunities possible as the imaging technology continues to advance.
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Affiliation(s)
- K L Andrew Chan
- Institute of Pharmaceutical Science, King's College London, SE1 9NH, UK
| | - Sergei G Kazarian
- Department of Chemical Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK.
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8
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Kazarian SG, Chan KLA. ATR-FTIR spectroscopic imaging: recent advances and applications to biological systems. Analyst 2013; 138:1940-51. [DOI: 10.1039/c3an36865c] [Citation(s) in RCA: 267] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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9
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Walsh MJ, Kajdacsy-Balla A, Holton SE, Bhargava R. Attenuated total reflectance Fourier-transform infrared spectroscopic imaging for breast histopathology. VIBRATIONAL SPECTROSCOPY 2012; 60:23-28. [PMID: 22773893 PMCID: PMC3388548 DOI: 10.1016/j.vibspec.2012.01.010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Histopathology forms the gold standard for the diagnosis of breast cancer. Fourier Transform Infrared (FT-IR) spectroscopic imaging has been proposed to be a potentially powerful adjunct to current histopathological techniques. Most studies using FT-IR imaging for breast tissue analysis have been in the transmission or transmission-reflection mode, in which the wavelength and optics limit the data to a relatively coarse spatial resolution (typically, coarser than 5 μm × 5 μm per pixel). This resolution is insufficient to examine many histologic structures. Attenuated Total Reflectance (ATR) FT-IR imaging incorporating a Germanium optic can allow for a four-fold increase in spatial resolution due to the material's high refractive index in the mid-IR. Here, we employ ATR FT-IR imaging towards examining cellular and tissue structures that constitute and important component of breast cancer diagnosis. In particular, we resolve and chemically characterize endothelial cells, myoepithelial cells and terminal ductal lobular units. Further extending the ability of IR imaging to examine sub-cellular structures, we report the extraction of intact chromosomes from a breast cancer cells and their spatially localized analysis as a novel approach to understand changes associated with the molecular structure of DNA in breast cancer.
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Affiliation(s)
- Michael J. Walsh
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL
| | | | - Sarah E. Holton
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL
| | - Rohit Bhargava
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL
- University of Illinois Cancer Center, University of Illinois at Urbana-Champaign, Urbana, IL
- Electrical and Computer Engineering, Mechanical Science and Engineering and Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL
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10
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Kong R, Bhargava R. Characterization of porcine skin as a model for human skin studies using infrared spectroscopic imaging. Analyst 2011; 136:2359-66. [DOI: 10.1039/c1an15111h] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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11
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Kong R, Reddy RK, Bhargava R. Characterization of tumor progression in engineered tissue using infrared spectroscopic imaging. Analyst 2010; 135:1569-78. [PMID: 20498913 PMCID: PMC3030988 DOI: 10.1039/c0an00112k] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Engineered tissues can provide models for imaging and disease progression and the use of such models is becoming increasingly prevalent. While structural characterization of these systems is documented, a combination of biochemical and structural knowledge is often helpful. Here, we apply Fourier transform infrared (FT-IR) spectroscopic imaging to examine an engineered tissue model of melanoma. We first characterize the biochemical properties and spectral changes in different layers of growing skin. Second, we introduce malignant melanocytes to simulate tumor formation and growth. Both cellular changes associated with tumor formation and growth can be observed. In particular, chemical changes associated with tumor-stromal interactions are observed during the course of tumor growth and appear to influence a 50-100 microm region. The development of this analytical approach combining engineered tissue with spectroscopy, imaging and computation will allow for quality control and standardization in tissue engineering and novel scientific insight in cancer progression.
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Affiliation(s)
- Rong Kong
- Department of Bioengineering and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Rohith K. Reddy
- Department of Bioengineering and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Rohit Bhargava
- Department of Bioengineering and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
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12
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Palombo F, Danoux CB, Weinberg PD, Kazarian SG. Measurement of drug and macromolecule diffusion across atherosclerotic rabbit aorta ex vivo by attenuated total reflection-Fourier transform infrared imaging. JOURNAL OF BIOMEDICAL OPTICS 2009; 14:044008. [PMID: 19725720 DOI: 10.1117/1.3174395] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Diffusion of two model drugs-benzyl nicotinate and ibuprofen-and the plasma macromolecule albumin across atherosclerotic rabbit aorta was studied ex vivo by attenuated total reflection-Fourier transform infrared (ATR-FTIR) imaging. Solutions of these molecules were applied to the endothelial surface of histological sections of the aortic wall that were sandwiched between two impermeable surfaces. An array of spectra, each corresponding to a specific location in the section, was obtained at various times during solute diffusion into the wall and revealed the distribution of the solutes within the tissue. Benzyl nicotinate in Ringer's solution showed higher affinity for atherosclerotic plaque than for apparently healthy tissue. Transmural concentration profiles for albumin demonstrated its permeation across the section and were consistent with a relatively low distribution volume for the macromolecule in the middle of the wall. The ability of albumin to act as a drug carrier for ibuprofen, otherwise undetected within the tissue, was demonstrated by multivariate subtraction image analysis. In conclusion, ATR-FTIR imaging can be used to study transport processes in tissue samples with high spatial and temporal resolution and without the need to label the solutes under study.
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Affiliation(s)
- Francesca Palombo
- Imperial College London, Department of Chemical Engineering and Chemical Technology, South Kensington Campus, London, SW7 2AZ, United Kingdom
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13
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Tetteh J, Mader K, Andanson JM, McAuley W, Lane M, Hadgraft J, Kazarian S, Mitchell J. Local examination of skin diffusion using FTIR spectroscopic imaging and multivariate target factor analysis. Anal Chim Acta 2009; 642:246-56. [DOI: 10.1016/j.aca.2009.03.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2008] [Revised: 02/26/2009] [Accepted: 03/03/2009] [Indexed: 01/12/2023]
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14
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Andanson JM, Hadgraft J, Kazarian SG. In situ permeation study of drug through the stratum corneum using attenuated total reflectance [corrected] Fourier transform infrared spectroscopic imaging. JOURNAL OF BIOMEDICAL OPTICS 2009; 14:034011. [PMID: 19566304 DOI: 10.1117/1.3130324] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Infrared (IR) spectroscopy is one of the most chemically specific analytical methods that gives information about composition, structure, and interactions in a material. IR spectroscopy has been successfully applied to study the permeation of xenobiotics through the skin. Combining IR spectroscopy with an IR array detector led to the development of Fourier transform infrared (FTIR) spectroscopic imaging, which generates chemical information from different areas of a sample at the microscopic level. This is particularly important for heterogeneous samples, such as skin. Attenuated total reflectance [corrected] (ATR)-FTIR imaging has been applied to measure, in situ, the diffusion of benzyl nicotinate (BN) through the outer layer of human skin [stratum corneum (SC)]. In vitro experiments have demonstrated the heterogeneous distribution of SC surface lipids before the penetration of a saturated solution of BN. Image analysis demonstrated a strong correlation between the distribution of lipids and drugs, while ethanol appeared to be homogenously distributed in the SC. These results show the ability of ATR-FTIR imaging to measure simultaneously the affinities of drug and solvent to the lipid-rich and lipid-poor skin domains, respectively, during permeation. This information may be useful in better understanding drug-diffusion pathways through the SC.
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Affiliation(s)
- Jean-Michel Andanson
- Imperial College London, Department of Chemical Engineering, South Kensington Campus, London SW7 2AZ, United Kingdom
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15
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Shah NB, Wolkers WF, Morrissey M, Sun WQ, Bischof JC. Fourier Transform Infrared Spectroscopy Investigation of Native Tissue Matrix Modifications Using a Gamma Irradiation Process. Tissue Eng Part A 2008. [DOI: 10.1089/ten.tea.2008.0158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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16
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Boncheva M, Tay FH, Kazarian SG. Application of attenuated total reflection Fourier transform infrared imaging and tape-stripping to investigate the three-dimensional distribution of exogenous chemicals and the molecular organization in Stratum corneum. JOURNAL OF BIOMEDICAL OPTICS 2008; 13:064009. [PMID: 19123656 DOI: 10.1117/1.3006072] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Attenuated total reflection Fourier transform infrared spectroscopic imaging combined with tape-stripping is an advantageous approach to map the depth penetration and lateral distribution of topically applied chemicals in Stratum corneum (SC) and the conformational order of SC lipids. Tape-stripping progressively removes layers of SC, and chemical imaging provides spatially resolved information on the chemical composition of both the newly exposed SC surface and of the tapes used for stripping. The procedure is rapid, minimally invasive, and does not necessitate cross-sectioning of the skin. This approach offers a simple and direct way to determine the distribution of exogenous volatile and non-volatile chemicals in SC as a function of the chemical composition of the formulation and time, and the conformational order of SC lipids in native and topically treated skin. The procedure described here is well suited to address questions of relevance for the areas of drug delivery, dermatology, and skin care.
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Affiliation(s)
- Mila Boncheva
- Firmenich SA Corporate R&D Division, PO Box 239, Route des Jeunes 1, CH-1211 Geneva 8 Switzerland.
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17
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Chan KLA, Kazarian SG. Attenuated total reflection-Fourier transform infrared imaging of large areas using inverted prism crystals and combining imaging and mapping. APPLIED SPECTROSCOPY 2008; 62:1095-1101. [PMID: 18926018 DOI: 10.1366/000370208786049042] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Attenuated total reflection-Fourier transform infrared (ATR-FT-IR) imaging is a very useful tool for capturing chemical images of various materials due to the simple sample preparation and the ability to measure wet samples or samples in an aqueous environment. However, the size of the array detector used for image acquisition is often limited and there is usually a trade off between spatial resolution and the field of view (FOV). The combination of mapping and imaging can be used to acquire images with a larger FOV without sacrificing spatial resolution. Previous attempts have demonstrated this using an infrared microscope and a Germanium hemispherical ATR crystal to achieve images of up to 2.5 mm x 2.5 mm but with varying spatial resolution and depth of penetration across the imaged area. In this paper, we demonstrate a combination of mapping and imaging with a different approach using an external optics housing for large ATR accessories and inverted ATR prisms to achieve ATR-FT-IR images with a large FOV and reasonable spatial resolution. The results have shown that a FOV of 10 mm x 14 mm can be obtained with a spatial resolution of approximately 40-60 microm when using an accessory that gives no magnification. A FOV of 1.3 mm x 1.3 mm can be obtained with spatial resolution of approximately 15-20 microm when using a diamond ATR imaging accessory with 4x magnification. No significant change in image quality such as spatial resolution or depth of penetration has been observed across the whole FOV with this method and the measurement time was approximately 15 minutes for an image consisting of 16 image tiles.
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Affiliation(s)
- K L Andrew Chan
- Department of Chemical Engineering, Imperial College London, London, SW7 2AZ, UK
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18
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Boncheva M, Damien F, Normand V. Molecular organization of the lipid matrix in intact Stratum corneum using ATR-FTIR spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:1344-55. [PMID: 18298945 DOI: 10.1016/j.bbamem.2008.01.022] [Citation(s) in RCA: 169] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2007] [Revised: 01/22/2008] [Accepted: 01/28/2008] [Indexed: 10/22/2022]
Abstract
ATR-FTIR spectroscopy is useful in investigating the lateral organization of Stratum corneum (SC) lipids in full-thickness skin. Based on studies of the thermotropic phase transitions in n-tricosane and in excised human skin, the temperature dependence of the CH2 scissoring bandwidth emerged as a measure of the extent of orthorhombic and hexagonal phases. This dependence provides a simpler measure of the lateral order in lipid assemblies than the common spectroscopic approaches based on difference spectra, curve fitting of the CH2 scissoring region, and the position of the CH2 stretching vibrations. It has the advantages of ease of determination, relatively low variability, and high discriminative power for the type of lateral intermolecular chain packing. A comparison of the lateral organization of the lipids at the SC surface of mammalian skin using the scissoring bandwidth revealed considerable differences between human abdominal skin (containing mostly orthorhombic phases), porcine ear skin (containing mostly hexagonal phases), and reconstructed human epidermis (containing mostly disordered phases). This parameter also correctly described the different effects of propylene glycol (minimally disturbing) and oleic acid (formation of a highly disordered phase) on the SC lipids in excised human skin. The procedure described here is applicable to in vivo studies in the areas of dermatology, transdermal drug delivery, and skin biophysics.
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Affiliation(s)
- Mila Boncheva
- Corporate R&D Division, Firmenich SA, P.O. Box 239, Route des Jeunes 1, CH-1211 Geneva 8, Switzerland.
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