M.J. Pilling

Comparison of transmission and transflectance mode FTIR imaging of biological tissue

FTIR microscopy is a powerful technique which has become popular due to its ability to provide complementary information during histopathological assessment of biomedical tissue samples. Recently however, questions have been raised on the suitability of the transflection mode of operation for clinical diagnosis due to the so called Electric Field Standing Wave (EFSW) effect. In this paper we compare chemical images measured in transmission and transflection from prostate tissue obtained from five different patients, and discuss the variability of the spectra acquired with each sampling modality. We find that spectra obtained in transflection undergo a non-linear distortion, i.e. non-linear variations in absorption band strength across the spectra, and that there are significant differences in spectra measured from the same area of tissue depending on the mode of operation. Principal Component Analysis (PCA) is used to highlight that poorer discrimination between benign and cancerous tissue is obtained in transflection mode. In addition we show that use of second derivatives, while qualitatively improves spectral discrimination, does not completely alleviate the underlying problem.

The origin of inverse absorption bands observed in the far-infrared RAIRS spectra of SnCl4 and SnBr4 adsorbed on thin-film SnO2 surfaces

The adsorption of SnCl4 and SnBr4 on polycrystalline SnO2 has been studied using synchrotron radiation based far-infrared reflection absorption infrared spectroscopy FIR-RAIRS. In order to exploit the sensitivity advantages of the buried metal layer method, the SnO2 is in the form of a thin film deposited on a tungsten foil substrate. Adsorption of SnCl4 and SnBr4 on an oxygen sputtered surface at 120 K results in spectra characteristic of condensed multilayers. In addition, both spectra exhibit an inverse absorption band centred at 355 cm(-1). Modified 4-layer, wavelength-dependent, Greenler calculations show that this inverse absorption band is induced by the presence of the adsorbate but is characteristic of the SnO2 layer. The lack of any frequency shift upon changing the adsorbate from SnCl4 to SnBr4 rules out the possibility that the inverse absorption band is due to a dipole-forbidden parallel mode of the molecule excited via the interaction with free electron oscillations in the metal, resulting from the radiation induced oscillating electric field just below the surface

A far-infrared RAIRS investigation of SnCl4 and water on thin-film carbon and silica surfaces

Far-infrared RAIRS spectroscopy employing synchrotron radiation as a soul ee, has been used to study the interaction of SnCl4, and water on thin-him silica and carbon surfaces. This has been made possible by growing the thin films on a highly reflecting tungsten substrate, enabling the conventional RAIRS geometry to be used. In addition to the observation of a strongly chemisorbed species on the silica surface the spectra from both surfaces indicate the presence of a more weakly bound complex containing both water and SnCl4

A far-infrared RAIRS investigation of SnCl4 on a silica surface using the buried metal layer approach

Far-infra red RAIRS spectroscopy employing synchrotron radiation as a source, has been used to study the interaction of SnCl4 on a thin-him silica surface. This has been made possible by growing the silica film on a highly reflecting tungsten substrate, enabling the conventional RAIRS geometry to be used. We show that reasonable S/N RAIRS spectra can be obtained in this region, even from films up to 1000 thick, enabling subtle details in the spectrum of the chemisorbed species to be obtained

Anomalous inverse absorption features in the far-infrared RAIRS spectra of SnCl4 on thin-film SnO2 surfaces

As part of a study of the chemistry of tin oxide chemical vapor deposition precursors at oxide surfaces, we have utilized the so-called buried metal layer approach to obtain far-IR reflection absorption infrared spectroscopy (RAIRS) spectra for SnCl4 adsorbed at a tin oxide surface supported on a polycrystalline tungsten foil. Two types of surface preparation—namely, sputtering with Ar or O2—have been used to clean the tin oxide surfaces prior to experiment. On O2-sputtered surfaces at 300 K, the spectra are dominated by an inverse-absorption feature in the form of a positive-going band in the spectrum, obtained via the ratio of the sample spectrum to that of the clean surface background. At low temperature, the spectra display both the positive-going inverse-absorption feature and the normal negative-going absorption features common to many RAIRS studies from metallic surfaces. On an Ar-sputtered surface, the inverse absorption band is not observed, but is replaced, at least at 300 K, by an absorption ba...

FTIR imaging of the molecular burden around Aβ deposits in an early-stage 3-Tg-APP-PSP1-TAU mouse model of Alzheimer's disease.

Alzheimers disease is one of the major causes of dementia in the elderly. The disease is caused by the misfolding of water soluble alpha-helical proteins, which leads to the accumulation of β-sheets in the form of amyloid plaques, which can subsequently affect surrounding tissue areas by oxidative stress neurotoxicity. The aim of the present study was to design a novel methodology to analyze the extent to the neuronal burden around protein-rich Aβ plaques suspected to affect molecular components by oxidative stress induced by inflammatory states. To do so, sagittal brain tissue sections from triple transgenic APPxPSP1xTAU mice were used to carry high magnification FTIR-FPA bench-top chemical imaging. The study used the combination of chemometric procedures involving spectral curve fitting and image processing to study the molecular changes occurring around the plaques. The study shows the performance of the approach by demonstrating its usefulness to co-localize molecular changes to different areas around the plaques. The results, although very preliminary, point to the strong interplay between the distance from the plaque and co-accumulation of molecular components indicative of inflammatory states.

Exploiting CELLULOSE SYNTHASE (CESA) class-specificity to probe cellulose microfibril biosynthesis

Mutagenesis reveals which CESA protein classes have the greatest influence on the regulation of cellulose microfibril biosynthesis in the Arabidopsis secondary cell wall. Cellulose microfibrils are the basic units of cellulose in plants. The structure of these microfibrils is at least partly determined by the structure of the cellulose synthase complex. In higher plants, this complex is composed of 18 to 24 catalytic subunits known as CELLULOSE SYNTHASE A (CESA) proteins. Three different classes of CESA proteins are required for cellulose synthesis and for secondary cell wall cellulose biosynthesis these classes are represented by CESA4, CESA7, and CESA8. To probe the relationship between CESA proteins and microfibril structure, we created mutant cesa proteins that lack catalytic activity but retain sufficient structural integrity to allow assembly of the cellulose synthase complex. Using a series of Arabidopsis (Arabidopsis thaliana) mutants and genetic backgrounds, we found consistent differences in the ability of these mutant cesa proteins to complement the cellulose-deficient phenotype of the cesa null mutants. The best complementation was observed with catalytically inactive cesa4, while the equivalent mutation in cesa8 exhibited significantly lower levels of complementation. Using a variety of biophysical techniques, including solid-state nuclear magnetic resonance and Fourier transform infrared microscopy, to study these mutant plants, we found evidence for changes in cellulose microfibril structure, but these changes largely correlated with cellulose content and reflected differences in the relative proportions of primary and secondary cell walls. Our results suggest that individual CESA classes have similar roles in determining cellulose microfibril structure, and it is likely that the different effects of mutating members of different CESA classes are the consequence of their different catalytic activity and their influence on the overall rate of cellulose synthesis.

Far-infrared reflection-absorption investigation of SnCl4 on silica and Na-modified silica surfaces using the buried metal layer approach

One of the key reactions in the CVD growth of SnO2 on glass is that between SnCl4 and H2O. Exploiting the buried metal layer approach, we have used far-infrared RAIRS at the Daresbury synchrotron, to study the initial steps in this process on model glass surfaces, consisting of thin (approximately 500 - 1000 angstroms) SiO2 films and Na covered SiO2 films grown on a tungsten substrate.