The application of standard two-way curve resolution methods is reported for analysis of three-way Raman image data. Two current curve resolution methods are described: principal factor multivariate curve resolution (PF-MCR), which uses principal factor analysis (PFA) combined with varimax rotation and alternating least-squares optimization (ALS), and orthogonal projection multivariate curve resolution (OP-MCR), which uses a Gram–Schmidt modified orthogonal projection approach (OPA) followed by ALS. The OP-MCR technique is shown to be an extremely rapid method of analysis producing results equivalent to those of PF-MCR in one-third to one-fourth the time. The results from MCR analysis using either method provide the number of chemical species present in the sample, the spectrum of each species for identification, and the concentration image for each species. The additional benefit of image noise reduction also results from the MCR techniques. A brief description of the theory is presented followed by analysis and comparison of results for two real Raman image data. A discussion is given addressing the rapid analysis aspects of OP-MCR and the relative merits and drawbacks of the technique in comparison to PF-MCR. The use of data subsampling is also discussed as a way of decreasing analysis time without loss in accuracy or performance.
The use of Raman microscopy in imaging two emulsion systems is described. Registered optical microscopy and Raman images are collected, the latter describing the chemical basis of the heterogeneity observed in the former. These examples act as a powerful demonstration of the application of the Raman microscopy technique to the analysis and understanding of microstructure in commercial products. The results indicate how the principles of Raman imaging can be applied to complex, multicomponent, multiphase systems of inherently low contrast. Such systems are of importance because they represent a wide variety of commercial product systems, ranging from pharmaceutical creams through skin creams and toothpastes. The use of a software environment for the organization, storage, management, interrogation, and manipulation of multidimensional spectral imaging data is also described. The important factors to be considered in determining the full information content of such data sets are established, and suggestions as to how such data sets can be optimally interrogated are made.
Step-scan Fourier Transform Inflared (FT-IR) Photoacoustic Spectroscopy (PAS) has been used to study the penetration of substances through abdominal pig skin. The experiments were performed in vitro and dimethylsulfoxide(DMS0) was applied either onto the surface or the bottom of the sample. The results demonstrated that DMSO propagated fast through the skin from the bottom sur$ace. The ease of identijication of this substance in this spectral range showed the potential of the technique, suggesting that penetration and distribution of other chemicals through the skin can be investigated by FT-IR PAS.Penetration and interaction of substances through skin have been investigated both for medical and cosmetic purposes, but the mechanism involved is not well understood [l,2]. Based on its ability to perform depth profile analysis, PAS has already been shown to be suitable for the study of penetration of topically applied substances into skin[3-51. Giese et al, for example, have studied the penetration of sunscreen into human skin, in the visible spectral range [S].The absorption bands from specific group components of substances are easily identified in the infrared spectral range, and a technique such as photoacoustic spectroscopy, which provides depth profile analysis in this range, may be convenient to study the distribution of substances through the skin. .
Raman microscopy and imaging couples the spatial resolution of optical microscopy with the spectral resolution and information content of Raman spectroscopy. Together, a powerful tool for the investigation of chemical, or molecular, heterogeneity is created. Raman microspectroscopy enables the nondestructive analysis of small quantities of sample and the identification of contaminants and inclusions in situ within a matrix – both of great importance and utility in forensic investigations. Perhaps more importantly, it has been recognized that the microheterogeneity of products has an influence on both product performance and appearance. In the analysis of complex, multiphase systems, optical microscopy contrast methods (the majority of which depend upon refractive index changes) are commonly employed to provide information on the structural organization of materials. However, information on the chemical organization of materials is then often based on conjecture. Raman microscopy is arguably the most easily applied of a family of techniques that use the innate spectral signatures of the components as a contrast element and hence provides a method for analyzing chemical heterogeneity in “real” systems. Typically, the information that would be appropriate from an investigation of chemical heterogeneity would be: the number of chemical components present; the pure spectrum of each component; spatially resolved concentration information for each individual component. Raman microscopy and imaging provides a tool to determine these important factors in complex, multiphase systems. In its simplest form, the Raman microspectroscopy experiment requires a laser to be focused down to a diffraction‐limited spot on a sample and the inelastically scattered light is collected from that point and analyzed. This generates a Raman spectrum, which is indicative of the identity and quantity of the molecular species present in that sample volume. The limiting spatial resolution that can be obtained is of the order of 1 µm in the lateral plane and 2 µm in the axial plane, the microscopes used lending themselves to a confocal optical arrangement that provides this level of depth discrimination. The information content is constrained to that available in the Raman vibrational spectra and so commonly molecules with distinct functional groups are clearly distinguished, whilst it is more difficult to distinguish specifically between molecules with very similar molecular structure and chemical functionality. It is also a commonly held belief that Ramaninvestigations are hampered by fluorescence interference, which obscures the Raman spectrum. However, with modern Raman microscopes there are few samples where this limitation becomes completely defeating. Several approaches to the generation of Raman images (images where the contrast is based on the chemical or molecular heterogeneity) have been established and are discussed in detail. A comparison is made between these different Raman imaging approaches and also with different spectral imaging methods.
Summary Opto-thermal transient radiometry (OTTER) is a non-invasive measurement technique, well suited for in vivo skin research. Its excitation and detection wavelengths can be selected to give a high sensitivity to stratum corneum hydration. This is demonstrated with measurements of hydration changes resulting from occlusion with a neoprene cover and with a topical application of an occlusive preparation. In the former case, the hydration was found to recover to normal levels upon exposure to atmospheric conditions in a characteristic time of 15 min. In the latter case, a topical application of petroleum jelly was found to lead to a doubling of stratum corneum hydration over 2h. This ability to measure hydration changes in the presence of topical hydrating agents is thought to be a particularly valuable property of the OTTER technique. With a different choice of excitation and detection wavelengths, OTTER can be used to measure skin thickness, from the surface down to the vascular bed. This technique was used to measure a skin thickness map of the ventral surface of the forearm of a volunteer, showing distinct thickening near the wrist and ulna. Another use of this technique is the study of changes in subcutaneous blood distribution associated with erythema. As a demonstration of this, blood distribution changes brought about by the topical application of a salicylate/nicotinate preparation were studied. The main finding is that the subcutaneous blood spreads towards the surface, with the mean depth decreasing from 63 mum to 55mum.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.