Alzheimer’s disease (AD) is characterized by the presence of extracellular deposits of amyloid-beta peptides (known as AD plaques). Its assessment is usually achieved post-mortem, requiring chemical pre-treatment via an antibody or indirect labelling. Label-free imaging techniques, like auto-fluorescence, spontaneous Raman (SpR) and stimulated Raman (SRS) imaging could be performed on tissue in its native state to study the biomolecular composition of AD plaques and contribute to a better understanding of the disease. Here we present imaging results of human brain amyloid core plaques. We show blue and green autofluorescence emission localized at the same plaque position while Raman spectroscopy revealed the presence of carotenoids at the same spot. For identifying the underlying carotenoids, first carotenoid reference spectra in hexane solution and then adsorbed on aggregated Aβ42 peptides were recorded. From the six carotenoids measured, lycopene matched closest with the Raman peak positions observed in the measured AD plaque. Furthermore, we used SRS to investigate the presence of a lipid halo around plaque locations as reported in literature for transgenic AD mice.
Environmental pollution by microplastics (MPs) represents a serious burden of the 21st century. Sensing the interactions of photosynthetic organisms with MPs is based on the study of their endogenous fluorescence derived from chlorophylls. Fluorescently labelled custom-made MPs were tested. We also recorded endogenous fluorescence of the moss in the presence of “naturally-occurring” MPs (polyethylene content of 2 mg/g, non fluorescent) in suspended matter (SM) from the river Rhine. Performed experiments evaluated the distribution of the MPs, as well as the sensitivity of endogenous fluorescence of chlorophylls to their presence. Understanding the interaction of living organisms with MPs will help to assess the impact of this environmental pollution and eventually to propose new approaches for its removal from water sources.
This conference presentation, “Stimulated Raman scattering simulation for imaging optimization” was prepared for the Biomedical Spectroscopy, Microscopy, and Imaging II conference at SPIE Photonics Europe 2022.
This conference presentation, “Label-free stimulated Raman scattering imaging utilized for correlating silicone content in breast tissue with capsular contracture in an intra-patient study” was prepared for the Biomedical Spectroscopy, Microscopy, and Imaging II conference at SPIE Photonics Europe 2022.
Light microscopes don’t have the ability to identify silicone (PDMS) particles from implants in histological slides. We describe a label-free method based on stimulated Raman scattering microscopy to locate and identify silicone in breast tissue.
Label-free imaging of Alzheimer’s disease (AD) brain tissue could contribute to a better understanding of its pathology. Here, we present a comprehensive study of sequentially applied spectroscopic and imaging modalities on snap-frozen AD tissue.
Alzheimer’s disease (AD) is the most common form of dementia, which is one of the main death leading causes with around 46 million people affected worldwide. Alzheimer’s disease is characterized by the accumulation of extracellular deposits of proteins in the brain, known as amyloid-beta (Aβ) plaques. Currently, in-vivo detection of Aβ pathology is solely possible by two invasive techniques: the analysis of cerebral fluid or PET imaging. Raman spectroscopy may be an alternative way of in-vivo diagnosis of Aβ deposits as it is sensitive to concentrations of biomolecules. It is an established and common non-destructive technique, which in addition allows for minimal sample preparation. Recent publications on transgenic mouse and human AD brain tissue suggest that Raman spectroscopy is an adequate technique to identify and localize Aβ plaques1,2. However, publications on human tissue lack the proof of plaque existence at the same location, imaged with Raman spectroscopy. The present study is designed to confirm ultimately a match between Raman spectra and possible amyloid-beta plaque locations. This is achieved by superimposing the autofluorescence image, the Raman imaging map and the stained fluorescence image of the same tissue section. Additionally, obtained data will be compared to previous studies of post mortem human AD brain tissue that was formalin fixed and paraffin embedded.
Dementia is one of the main death leading causes worldwide and Alzheimer’s disease (AD) is its most common form. In postmortem examinations of AD brain tissue, extracellular deposits of proteins are observed, known as amyloid-beta (Aß) plaques. Aß plaques are characterized by their occurrence of beta-sheets and are, beside tau tangles, biological hallmarks in the postmortem diagnosis of AD. Little research on the detectability of Aß deposits in brain tissue using Raman spectroscopy has been published.
Here, we examined formalin fixed, paraffin embedded tissue slices of AD and healthy control cases. The slices have been spectrally raster imaged with a step size smaller the size of a plaque using a commercial Raman spectroscope with a NIR laser source to obtain a hyperspectral map of the size of 0.5mm2. Specific band intensities including, among others, protein and lipid components were analyzed and afterward compared to the healthy control cases to study spectral differences. Further, Aß deposit locations could be precisely matched to the obtained spectral data by staining the same Raman imaged tissue slice with Thioflavin afterward. In addition, plaques can be co-localized by using histochemical stained adjacent tissue slices.
In conclusion, we present new insights on spectral changes in the Raman fingerprint region of 950 to 1800cm-1 when analyzing the molecular composition of AD brain tissue.
Exposure to polycyclic aromatic hydrocarbons (PAHs) is considered a serious threat to the health of animals and humans and should be thoroughly monitored. Next to chemical analysis of PAHs in the various environmental compartments, PAH metabolites in body fluids (e.g., bile and urine) could be measured to determine the actual uptake. Although pyrene is not considered particularly toxic, its metabolite 1-hydroxy pyrene is often used as a biomarker because it is usually found at considerable concentrations and the analysis is relatively simple. As the result of differences in volatility and/or solubility, the uptake of more relevant carcinogens like benzo(a)pyrene may be some orders of magnitude lower and is far more difficult to measure. Determination of benzo(a)pyrene metabolites requires a very selective and sensitive method, and so far these compounds could only be detected after exposure to heavy pollution. In this paper it will be shown how several hydroxy benzo(a)pyrene metabolites are selectively determined using Shpol'skii spectroscopy. With this method, highly resolved fluorescence spectra are obtained upon cooling the sample in a suitable solvent to cryogenic temperatures. When a tunable laser system is employed as an excitation source, sub- femtomole amounts can be detected. Applications of the technique to marine monitoring (benzo(a)pyrene metabolites in fish bile) and to occupational hygienics (benzo(a)pyrene metabolites in workers' urine) are discussed. The data will be compared with 1-hydroxy pyrene concentrations to evaluate the routine use of the latter compound as a biomarker.
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