Label-free polarisation-resolved optical imaging of biological samples

Content Provider	Semantic Scholar
Author	Vito, Giuseppe De
Copyright Year	2016
Abstract	Myelin is a biological structure present in all the gnathostomata. It is a highlyordered structure, in which many lipid-enriched and densely compacted phospholipid bilayers are rolled up in a cylindrical symmetry around a subgroup of axons. The myelin sheath increases the electrical transverse resistance and reduces the capacitance making the saltatory conduction of action potentials possible and therefore leading to a critically improved performance in terms of nervous impulse conduction speeds and travel lengths. Myelin pathologies are a large group of neurological diseases that often result in death or disability. In order to investigate the main causes of myelin damage and its temporal progression many microscopy techniques are currently employed, such as electron microscopy and histochemistry or fluorescence imaging. However, electron microscopy and histochemistry imaging require complex sample preparation and are therefore unsuitable for live imaging. Fluorescence imaging, as well as its derivatives, confocal and two-photon imaging, relies on the use of fluorescent probes to generate the image contrast but fluorophores and the associated sample processing, when applicable to living specimens, might nonetheless modify the biological properties of the target molecule and perturb the whole biological process under investigation; moreover, fluorescent immunostaining still requires the fixation of the cells. Coherent anti-Stokes Raman Scattering (CARS) microscopy, on the other hand, is a powerful and innovative imaging modality that permits the study of living specimens with excellent chemical contrast and spatial resolution and without the confounding and often tedious use of chemical or biological probes. This is particularly important in clinical settings, where the patient biopsy must be explanted in order to stain the tissue. In these cases it may be useful to resort to a set of label-free microscopy techniques. Among these, CARS microscopy is an ideal tool to investigate myelin morphology and structure, thanks to its abundance of CH2 bonds. The chemical selectivity of CARS microscopy is based on the properties of the contrast-generating CARS process. This is a nonlinear process in which the energy difference of a pair of incoming photons (“pump” and “Stokes”) matches the energy of one of the vibrational modes of a molecular bond of interest. This vibrational excited state is coherently probed by a third photon (“probe”) and anti-Stokes radiation is emitted.
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Language	English
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Resource Type	Article