Analytical applications of near-infrared spectroscopy and imaging
Near-infrared (NIR) spectroscopy provides the information of overtone and combination bands of C-H, O-H, S-H, C=O bond stretching and bending motions. Recent developments in conventional NIR spectroscopy integrate near and middle infrared focal plane array detectors and acousto-optic tunable filter (AOTF) and made it possible to develop an effective multispectral imaging instrument. Such techniques provide chemically specific images rapidly and non-invasively and contain spatial and spectroscopic information. For example, in our laboratory, we have demonstrated the versatility of multispectral imaging technique in the analysis of materials to detect inhomogeneity in terms of distribution and conformation. Biomolecules encapsulated in silica gel offer more advantages over liquid phase solutions for analytical applications. Although, these materials are made by dispersion of aqueous solution of biomolecules into the silica sot, their spatial distribution in terms of concentration and conformation determines its physical and chemical properties. We have developed multispectral imaging instrument (1850 nm to 2400 nm, spatial resolution of 10 X 10 microns/pixel) and used as a tool to detect inhomogeneity in terms of distribution and conformation in silica gel materials encapsulated with bovine serum albumin (BSA). Based on the spectral information collected from different areas of the images we detected the inhomogeneous distribution of BSA encapsulated in silica-gel materials. Using bio-mimetic functional group attached polystyrene resin particles we developed a model study that can potentially be used to detect cancer in early stages. For this purpose, we developed two different instruments. Namely, microscopic multispectral imaging instrument (1000-1750 nm region and spatial resolution of 0.91 ± 0.02 microns/pixel) and macroscopic multispectral imaging instrument (1700-2500 run region and spatial resolution of 22 ± 2 microns/pixel) in NIR region. Cassegrain based reflective objective was used to obtain the high spatial resolution of microscopic multispectral imaging instrument. Both of these instruments can simultaneously determine the inhomogeneity visually and as well as spectroscopically. We also introduced a novel method to encapsulate fullerenes in silica sol-gels that have number of applications in optics and electronics. It should also be noted that these materials must contain highly dispersed and homogeneous distribution of fullerenes to be effectively useful. Extending multispectral imaging technique to the visible region, we have developed another set of two different instruments in 420 nm to 990 nm region to analyze the prepared nano-composites. Namely, microscopic multispectral imaging instrument (spatial resolution of 0.8 X 0.8 microns/pixel) and macroscopic multispectral imaging instrument (spatial resolution of 10 X 10 microns/pixel) in NIR region. These instruments were been used to detect homogeneity of fullerene dispersions in prepared silica sol-gel nano-composites. Although, pure forms of fullerenes have a number of applications in various branches of science, they are extracted as mixture of fullerenes (C60 and C70 etc.,) when they are synthesized. Multivariate method of analysis has been used to determine the compositions of fullerene mixtures. We described and demonstrated a novel method that determines the compositions of different kinds of fullerenes by utilizing the combination of NIR spectrophotometry and multivariate analysis. It is not only a simple, inexpensive, accurate, and fast method but also a non-destructive method. Because of their high non-polar nature fullerenes are being used as reversed phase stationary phase for high performance liquid chromatography (HPLC) by covalently attaching them on to the silica surface. However, gas liquid chromatography (GLC) offers relatively faster analysis and high resolution values over LC. We used pure forms of fullerenes and functionalized fullerenes as stationary phases in GLC. We used room temperature ionic liquids (RTIL) to dissolve fullerenes and functionalized fullerenes and coated them as stationary phases to the walls of the fused silica capillary column. We observed that fullerene and functionalized fullerene containing columns show high resolution values in separation of different analyte mixtures over corresponding blank ionic liquid columns.
Santhosh K Challa,
"Analytical applications of near-infrared spectroscopy and imaging"
(January 1, 2007).
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