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ABSTRACT: Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging is a highly versatile, label free and non-destructive chemical imaging method which can be applied to study a wide range of samples and systems. This review summarises some of the recent advances and applications of this imaging method in the area of biomedical studies, including examples of section of aorta, skin tissue and live cells. Two of the major advantages of measuring in ATR mode are the opportunity to measure samples that absorb strongly in the IR spectrum, such as aqueous systems, without significant sample preparation and the ability to increase the spatial resolution of the measured image. The implications of these advantages as well as some limitations of this imaging approach are discussed and a brief outlook at some of the possible future developments in this area is provided.
The Analyst 04/2013; 138(7):1940-51. · 4.23 Impact Factor
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ABSTRACT: The label-free, non-destructive chemical analysis offered by FTIR spectroscopic imaging is a very attractive and potentially powerful tool for studies of live biological cells. FTIR imaging of live cells is a challenging task, due to the fact that cells are cultured in an aqueous environment. While the synchrotron facility has proven to be a valuable tool for FTIR microspectroscopic studies of single live cells, we have demonstrated that high quality infrared spectra of single live cells using an ordinary Globar source can also be obtained by adding a pair of lenses to a common transmission liquid cell. The lenses, when placed on the transmission cell window, form pseudo hemispheres which removes the refraction of light and hence improve the imaging and spectral quality of the obtained data. This study demonstrates that infrared spectra of single live cells can be obtained without the focus shifting effect at different wavenumbers, caused by the chromatic aberration. Spectra of the single cells have confirmed that the measured spectral region remains in focus across the whole range, while spectra of the single cells measured without the lenses have shown some erroneous features as a result of the shift of focus. It has also been demonstrated that the addition of lenses can be applied to the imaging of cells in microfabricated devices. We have shown that it was not possible to obtain a focused image of an isolated cell in a droplet of DPBS in oil unless the lenses are applied. The use of the approach described herein allows for well focused images of single cells in DPBS droplets to be obtained.
The Analyst 03/2013; · 4.23 Impact Factor
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ABSTRACT: This work uses ATR-FTIR spectroscopic imaging to study the dissolution of delayed release and pH resistant compressed coating pharmaceutical tablets. Tablets with an inner core and outer shell were constructed using a custom designed compaction cell. The core of the delayed release tablets consisted of hydroxypropyl methylcellulose (HPMC) and caffeine. The shell consisted of microcrystalline cellulose (MCC) and glucose. The core of the pH resistant formulations was an ibuprofen and PEG melt and the shell was constructed from HPMC and a basic buffer. UV/vis spectroscopy was used to monitor the lag-time and visible optical video imaging was used as a complementary imaging technique with a larger field of view. Two delayed release mechanisms were established. For tablets with soluble shell sections lag-time was dependent upon rapid shell dissolution. For tablets less soluble shells, the lag-time was controlled by the rate dissolution medium ingress through the shell and the subsequent expansion of the wet HPMC core. The pH resistant formulations prevented crystallization of the ibuprofen in the core during dissolution despite an acidic dissolution medium. FTIR imaging produced important information about the physical and chemical processes occurring at the interface between tablet sections during dissolution.
European journal of pharmaceutical sciences: official journal of the European Federation for Pharmaceutical Sciences 01/2013; · 2.61 Impact Factor
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ABSTRACT: Transmission mode is one of the most common sampling methods for FTIR spectroscopic imaging because the spectra obtained generally have a reasonable signal to noise ratio. However, dispersion and refraction of infrared light occurs when samples are sandwiched between infrared windows or placed underneath a layer of liquid. Dispersion and refraction cause infrared light to focus with different focal lengths depending on the wavelength (wavenumber) of the light. As a result, images obtained are in focus only at a particular wavenumber while they are defocused at other wavenumber values. In this work, a solution to correct this spread of focus by means of adding a lens on top of the infrared transparent window, such that a pseudo hemisphere is formed, has been investigated. Through this lens (or hemisphere), refraction of light is removed and the light across the spectral range has the same focal depth. Furthermore, the lens acts as a solid immersion objective and an increase of both magnification and spatial resolution (by 1.4 times) is demonstrated. The spatial resolution was investigated using an USAF resolution target, showing that the Rayleigh criterion can be achieved, as well as a sample with a sharp polymer interface to indicate the spatial resolution that can be expected in real samples. The reported approach was used to obtain chemical images of cross-sections of cancer tissue and hair samples sandwiched between infrared windows showing the versatility and applicability of the method. In addition to the improved spatial resolution, the results reported herein also demonstrate that the lens can reduce the effect of scattering near the edges of tissue samples. The advantages of the presented approach, obtaining FTIR spectroscopic images in transmission mode with the same focus across all wavenumber values and simultaneous improvement in spatial resolution, will have wide implications ranging from studies of live cells to sorption of drugs into tissues.
Analytical Chemistry 12/2012; · 5.86 Impact Factor
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ABSTRACT: Rapid, in situ, and label-free chemical analysis in microfluidic devices is highly desirable. FT-IR spectroscopic imaging has previously been shown to be a powerful tool to visualize the distribution of different chemicals in flows in a microfluidic device at near video rate imaging speed without tracers or dyes. This paper demonstrates the possibility of using this imaging technology to capture the chemical information of all reactants and products at different points in time and space in a two-phase system. Differences in the rates of chemical reactions in laminar flow and segmented flow systems are also compared. Neutralization of benzoic acid in decanol with disodium phosphate in water has been used as the model reaction. Quantitative information, such as concentration profiles of reactant and products, can be extracted from the imaging data. The same feed flow rate was used in both the laminar flow and segmented flow systems. The laminar flow pattern was achieved using a plain wide T-junction, whereas the segmented flow was achieved by introducing a narrowed section and a nozzle at the T-junction. The results show that the reaction rate is limited by diffusion and is much slower with the laminar flow pattern, whereas the reaction is completed more quickly in the segmented flow due to better mixing.
Analytical Chemistry 04/2012; 84(9):4052-6. · 5.86 Impact Factor
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ABSTRACT: The use of self-assembled monolayers is an established method to study the effect of surface properties on proteins and other biological materials. The generation of a monolayer with a gradient of chemical properties allows for the study of multiple surface properties simultaneously in a high throughput manner. Typically, in order to detect the presence of proteins or biological material on a surface, the use of additional dyes or tags is required. Here we present a novel method of studying the effect of gradient surface properties on protein adsorption and crystallization in situ through the use of ATR-FTIR spectroscopic imaging, which removes the need for additional labeling. We describe the successful application of this technique to the measurement of the growth of a gradient monolayer of octyltrichlorosilane across the surface of a silicon ATR element. ATR-FTIR imaging was also used to study the adsorption of lysozyme, as a model protein, onto the modified surface. The sensitivity of measurements obtained with a focal plane array (FPA) detector were improved though the use of pixel averaging which allowed small absorption bands to be detected with minimal effect on the spatial resolution along the gradient. Study of the effect of surface hydrophobicity on both adsorption of lysozyme to the element and lysozyme crystallization revealed that more lysozyme adsorbed to the hydrophobic side of the ATR element and more lysozyme crystals formed in the same region. These findings strongly suggest a correlation exists between surface protein adsorption and protein crystallization. This method could be applied to the study of other proteins and whole cells.
Langmuir 02/2012; 28(6):3174-9. · 4.19 Impact Factor
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ABSTRACT: The introduction of carbon nanotubes (CNTs) modifies bulk polymer properties, depending on intrinsic quality, dispersion, alignment, interfacial chemistry and mechanical properties of the nanofiller. These effects can be exploited to enhance the matrices of conventional microscale fibre-reinforced polymer composites, by using primary reinforcing fibres grafted with CNTs. This paper presents a methodology that combines atomic force microscopy, polarised Raman spectroscopy, and nanoindentation techniques, to study the distribution, alignment and orientation of CNTs in the vicinity of epoxy-embedded micrometre-scale silica fibres, as well as, the resulting local mechanical properties of the matrix. Raman maps of key features in the CNT spectra clearly show the CNT distribution and orientation, including a 'parted' morphology associated with long grafted CNTs. The hardness and indentation modulus of the epoxy matrix were improved locally by 28% and 24%, respectively, due to the reinforcing effects of CNTs. Moreover, a slower stress relaxation was observed in the epoxy region containing CNTs, which may be due to restricted molecular mobility of the matrix. The proposed methodology is likely to be relevant to further studies of nanocomposites and hierarchical composites.
Nanoscale 11/2011; 3(11):4759-67. · 5.91 Impact Factor
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ABSTRACT: This work presents the novel application of attenuated total reflection-Fourier transform infrared spectroscopic (ATR-FTIR) imaging to study the dissolution of ibuprofen form tablets in which the internal pH of the matrix has been modified by addition of acidic and basic powders to the formulations. Acidic additives to the matrix retarded the dissolution of crystalline ibuprofen domains. Basic additives formed both soluble and insoluble salts with the ibuprofen depending on the pH modifier added. Tablets consisting of hydroxypropyl methylcellulose, ibuprofen, and an acidic or basic additive were studied. FTIR imaging in ATR mode was used for analysis of water ingress into the tablet and the presence, distribution, and chemical state of the drug. The FTIR imaging data showed distinct changes in the dissolution of crystalline ibuprofen between the formulations with different pH modifiers. In the basic formulations, FTIR imaging identified the formation of salts. The sodium salt formed was highly soluble and enhanced dissolution, whereas the calcium salt was highly insoluble and slowed the dissolution. FTIR imaging has produced important data concerning the internal matrix dissolution performance.
Journal of Pharmaceutical Sciences 06/2011; 100(11):4745-55. · 3.06 Impact Factor
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ABSTRACT: Tip-enhanced Raman mapping is a powerful, emerging technique that offers rich chemical information and high spatial resolution. Currently, most of the successes in tip-enhanced Raman scattering (TERS) measurements are based on the inverted configuration where tips and laser are approaching the sample from opposite sides. This results in the limitation of measurement for transparent samples only. Several approaches have been developed to obtain tip-enhanced Raman mapping in reflection mode, many of which involve certain customisations of the system. We have demonstrated in this work that it is also possible to obtain TERS nano-images using an upright microscope (top-illumination) with a gold-coated Si atomic force microscope (AFM) cantilever without significant modification to the existing integrated AFM/Raman system. A TERS image of a single-walled carbon nanotube has been achieved with a spatial resolution of ∼ 20-50 nm, demonstrating the potential of this technique for studying non-transparent nanoscale materials.
Nanotechnology 04/2011; 22(17):175701. · 3.98 Impact Factor
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ABSTRACT: We have previously demonstrated that FT-IR spectroscopic imaging can be used as a powerful, label-free detection method for studying laminar flows. However, to date, the speed of image acquisition has been too slow for the efficient detection of moving droplets within segmented flow systems. In this paper, we demonstrate the extraction of fast FT-IR images with acquisition times of 50 ms. This approach allows efficient interrogation of segmented flow systems where aqueous droplets move at a speed of 2.5 mm/s. Consecutive FT-IR images separated by 120 ms intervals allow the generation of chemical movies at eight frames per second. The technique has been applied to the study of microfluidic systems containing moving droplets of water in oil and droplets of protein solution in oil. The presented work demonstrates the feasibility of the use of FT-IR imaging to study dynamic systems with subsecond temporal resolution.
Analytical Chemistry 03/2011; 83(9):3606-9. · 5.86 Impact Factor
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ABSTRACT: The aim of this study was to fabricate three-dimensional (3D) porous chitosan/poly(ε-caprolactone) (PCL) hydrogels with improved mechanical properties for tissue engineering applications. A modified emulsion lyophilisation technique was developed to produce 3D chitosan/PCL hydrogels. The addition of 25 and 50 wt% of PCL into chitosan substantially enhanced the compressive strength of composite hydrogel 160 and 290%, respectively, compared to pure chitosan hydrogel. The result of ATR-FTIR imaging corroborated that PCL and chitosan were well mixed and physically co-existed in the composite structures. The composite hydrogels were constructed of homogenous structure with average pore size of 59.7 ± 14 μm and finer pores with average size of 4.4 ± 2 μm on the wall of these larger pores. The SEM and confocal laser scanning microscopy images confirmed that fibroblast cells were attached and proliferated on the 3D structure of these composite hydrogels. The composite hydrogels acquired in this study possessed homogeneous porous structure with improved mechanical strength and integrity. They may have a high potential for the production of 3D hydrogels for tissue engineering applications.
Journal of Materials Science Materials in Medicine 02/2011; 22(2):279-88. · 2.32 Impact Factor
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ABSTRACT: Three-dimensional (3D) chemical information was obtained by means of a combination of two-dimensional attenuated total reflection Fourier transform infrared (ATR-FT-IR) imaging with a focal plane array detector and variable angle depth profiling. Since the penetration depth of the evanescent wave in ATR spectroscopy is not limited by diffraction, it was possible to resolve thin sandwiched polymer layers nondestructively within a stack of polymer layers. Chemical images were obtained from layers of different thickness of the laminate by moving a custom-made aperture to specific positions on the condenser lens of the ATR accessory. Sequences of absorption images detect the successive appearance of thin, buried layers of polybutylmethacrylate (d(PBMA) = 400 nm) and polycarbonate (d(TMPC) = 300 nm) in different depths of the stack of polymer layers. The depth resolution of variable-angle ATR-FT-IR imaging is sufficiently high to detect surface roughness at the interface between different polymer layers. Two different stacks of polymers with reordered sandwich-layers were imaged simultaneously, demonstrating the potential of variable angle ATR-FT-IR for 3D-imaging of a sample with xyz-heterogeneity, which can be a powerful analytical technique for materials science and biomedical research.
Langmuir 12/2010; 26(24):19027-32. · 4.19 Impact Factor
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ABSTRACT: Tip-enhanced Raman scattering (TERS) has emerged as a powerful analytical tool for measuring chemical images with nanometre spatial resolution. In this paper, the application of TERS to study differentiation of single-walled carbon nanotubes (SWCNTs) with 14 nm spatial resolution is demonstrated by the measurement of a mixture of two different types of SWCNTs as the model sample. The results demonstrate that TERS is a viable tool for the detection and localization of different SWCNTs and amorphous carbon in mixed SWCNTs based on the spectral differences in the radial breathing mode and the D bands.
Nanotechnology 11/2010; 21(44):445704. · 3.98 Impact Factor
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ABSTRACT: Details on how fluoride interferes in enamel mineralization are still controversial. Therefore, this study aimed at analyzing the organic contents of fluorosis-affected teeth using Fourier Transformation Infrared spectroscopy. To this end, 10 male Wistar rats were divided into two groups: one received 45 ppm fluoride in distilled water for 60 days; the other received distilled water only. Then, the lower incisors were removed and prepared for analysis by two FTIR techniques namely, transmission and micro-ATR. For the first technique, the enamel was powdered, whereas in the second case one fluorotic incisor was cut longitudinally for micro-ATR. Using transmission and powdered samples, FTIR showed a higher C-H content in the fluorotic enamel compared with control enamel (p<0.05, n=4 in the flurotic, and n=5 in the control group). Results from the micro-ATR-FTIR spectroscopic analysis on one longitudinally cut incisor carried out at six points reveal a higher C-H bond content at the surface of the enamel, with values decreasing toward the dentine-enamel junction, and reaching the lowest values at the subsuperficial enamel. These results agree with the morphological data, which indicate that in the rat incisor the fluorotic lesion is superficial, rather than subsuperficial, as in the case of human enamel. The results also suggest that the increased C-H bond content may extend toward the more basal enamel (intraosseous), indicating that fluorotic enamel may intrinsically contain more protein. Finally, particularly when coupled to ATR, FTIR is a suitable tool to study the rat incisor enamel, which is a largely used model of normal and abnormal amelogenesis. Further studies along this line may definitely answer some questions regarding protein content in fluorotic enamel as well as their origin.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 09/2010; 77(1):59-63. · 2.10 Impact Factor
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ABSTRACT: A versatile approach for the rapid prototyping of microfluidic devices suitable for use with FT-IR spectroscopic imaging is introduced. Device manufacture is based on the direct printing of paraffin onto the surface of an infrared transparent substrate, followed by encapsulation. Key features of this approach are low running costs, rapid production times, simplicity of design modifications and suitability for integration with FT-IR spectroscopic measurements. In the current experiments, the minimum width of channel walls was found to be approximately 120 mum and approximately 200 when a 25 mum and 12 mum spacer is used, respectively. Water and poly(ethylene glycol) are used as model fluids in a laminar flow regime, and are imaged in both transmission and attenuated total reflection (ATR) modes. It is established that adoption of transmission mode measurements yields superior sensitivity whilst the ATR mode is more suitable for quantitative analysis using strong spectral absorption bands. Results indicate that devices manufactured using this approach are suitable for use with in situ FT-IR spectroscopic imaging.
Lab on a Chip 08/2010; 10(16):2170-4. · 5.67 Impact Factor
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ABSTRACT: Fourier transform infrared (FT-IR) spectroscopic imaging has become a very powerful method in chemical analysis. In this review paper we describe a variety of opportunities for obtaining FT-IR images using the attenuated total reflection (ATR) approach and provide an overview of fundamental aspects, accessories, and applications in both micro- and macro-ATR imaging modes. The advantages and versatility of both ATR imaging modes are discussed and the spatial resolution of micro-ATR imaging is demonstrated. Micro-ATR imaging has opened up many new areas of study that were previously precluded by inadequate spatial resolution (polymer blends, pharmaceutical tablets, cross-sections of blood vessels or hair, surface of skin, single live cells, cancerous tissues). Recent applications of ATR imaging in polymer research, biomedical and forensic sciences, objects of cultural heritage, and other complex materials are outlined. The latest advances include obtaining spatially resolved chemical images from different depths within a sample, and surface-enhanced images for macro-ATR imaging have also been presented. Macro-ATR imaging is a valuable approach for high-throughput analysis of materials under controlled environments. Opportunities exist for chemical imaging of dynamic aqueous systems, such as dissolution, diffusion, microfluidics, or imaging of dynamic processes in live cells.
Applied Spectroscopy 05/2010; 64(5):135A-152A. · 1.66 Impact Factor
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ABSTRACT: The aim of this study was to develop a method for converting an amorphous drug to a crystalline form to enhance its stability and inhalation performance. Spray-dried amorphous salbutamol sulphate powder was conditioned with supercritical carbon dioxide (scCO(2)) modified with menthol. The effect of menthol concentration, pressure, temperature and time on the characteristics of the resulting salbutamol sulphate powder was investigated. Pure scCO(2) had no effect on the physical properties of amorphous salbutamol sulphate; however, scCO(2) modified with menthol at 150bar and 50 degrees C was efficient in converting amorphous drug to crystalline form after 12h of conditioning. The average particle size of powders decreased slightly after the conditioning process because of reducing agglomeration between particles by increasing surface roughness. Emitted dose measured by the fine particle fraction (FPF(emitted)) of amorphous salbutamol sulphate was enhanced from 32% to 43% after conditioning with scCO(2)+menthol and its water uptake was significantly decreased. This study demonstrates the potential of scCO(2)+menthol for converting amorphous forms of powders to crystalline, while preserving the particle size.
International journal of pharmaceutics 03/2010; 388(1-2):114-22. · 2.96 Impact Factor
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ABSTRACT: Elucidating the chemical composition of microfluidic flows is crucial in both understanding and optimising reactive processes within small-volume environments. Herein we report the implementation of a novel detection methodology based on Attenuated Total Reflection (ATR)-Fourier Transform Infra-Red (FTIR) spectroscopic imaging using an infrared focal plane array detector for microfluidic applications. The method is based on the combination of an inverted prism-shape ATR crystal with a poly(dimethylsiloxane)-based microfluidic mixing device. To demonstrate the efficacy of this approach, we report the direct measurement and imaging of the mixing of two liquids of different viscosities and the imaging and mixing of H2O and D2O with consecutive H/D isotope exchange. This chemically specific imaging approach allows direct analysis of fluid composition as a function of spatial position without the use of added labels or dyes, and can be used to study many processes in microfluidics ranging from reactions to separations.
Lab on a Chip 10/2009; 9(20):2909-13. · 5.67 Impact Factor
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ABSTRACT: Fouling in heat exchangers is a major economic problem for the crude oil industry. Despite significant research in this area, the fundamentals of the complex fouling process are not fully understood. There are many analytical techniques that are useful in the characterization of such deposits; however, each has its own limitations and drawbacks. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging has the advantage of being a nondestructive analytical technique with minimal sample preparation and, most importantly, is able to provide both chemical and spatial information about a sample. This paper introduces novel applications combining macro- and micro-ATR modes in FTIR imaging to characterize real deposits from a heat exchanger of a crude oil refinery. A lab-made aperture was utilized in macro-ATR imaging to correct the distortion of spectral bands that occurs for materials with a high refractive index, such as petroleum deposits. Using different ATR accessories for the macro (Golden Gate with a diamond crystal) and micro (germanium coupled to an infrared microscope) modes, FTIR imaging, with fields of view of 610 × 530 μm2 and 63 × 63 μm2, respectively, yields important information about the spatial distribution of different components in the deposits. Macro-ATR-FTIR imaging revealed clusters of chemically different compounds such as asphaltenes, carbonates, sulfates, sulfoxides, oxalates, and possibly coke. It was also demonstrated that with the enhanced spatial resolution of the micro-ATR approach, a more representative spectrum of the components can be achieved. Different forms of the oxalate functional group, one of which was barely at the detection limit of the macro-ATR approach, were also identified using the micro-ATR method. The sensitivity of the two modes of measurement with different spatial resolutions allows spatial and chemical information to be obtained and analyzed for domains of different sizes in studied samples.
08/2009;
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ABSTRACT: Attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopic imaging combined with a gelatine tape lift method was applied to fingermarks contaminated with various types of cosmetic residues and drugs. This approach allowed not only the imaging of partial fingermarks but also demonstrated the advantage of this chemical imaging methodology in being able to detect heterogeneously distributed localized compounds after surfaces contaminated with various types of cosmetics or drug residues had been handled. This is the first time that the detection of cosmetics in fingermarks deposited on nonporous and porous surfaces has been performed. These results show a potential extension of the applicability of ATR-FTIR imaging to forensic science. Copyright © 2009 John Wiley & Sons, Ltd.
Surface and Interface Analysis 08/2009; 42(5):386 - 392. · 1.18 Impact Factor
