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Posted: Jan 15, 2013
3D mapping of lipid orientation in biological tissues such as skin
(Nanowerk News) A non-invasive method that makes it possible to observe in situ how assemblies of lipids
are oriented in biological tissues, and which does not require any labeling or preparation,
has been developed by physicists from the Laboratoire d’Optique et Biosciences (CNRS /
Inserm / École Polytechnique).
Mapping of molecular orientation in an artificial lipid assembly using polarized third-harmonic generation (P-THG) microscopy (left). Diagram showing the molecular structure of a multilamellar lipid assembly (right). P-THG mapping of molecular orientation in an amalgamation of multilamellar lipid vesicles. This virtual optical section, obtained without labeling, shows that the molecules are oriented perpendicularly at the interfaces.
Multilamellar assemblies of lipids (fats) play a key role in certain physiological functions, not just within the
skin (which serves as a protective barrier against external aggressions) but also in the way neurons
function. The disorganization of these assemblies is often linked to serious pathologies. However, the
techniques normally used to determine the arrangement of molecules, such as X-ray scattering or nuclear
magnetic resonance, are not suitable for studying intact biological tissues with good cellular resolution. In
addition, they often require labeling and/or significant sample preparation.
First developed in the 1990s, multiphoton microscopy allows intact biological tissue to be observed in three
dimensions with sub-cellular resolution at depths exceeding several hundred micrometers. Researchers
from the Laboratoire d’Optique et Biosciences have identified a new indicator, known as P-THG (polarized
third-harmonic generation), which is sensitive to molecular order in multi-layer lipid assemblies. Thanks to
this optical contrast source, it is now possible to map the general orientation and degree of alignment of
lipid assemblies in three dimensions and also to observe their possible disorganization. This novel
multiphoton microscopy technique thus provides a non-invasive tool for probing molecular alignment in situ in biological media.
This approach enables scientists to map, with unparalleled sensitivity and contrast, the organization of lipids in human skin biopsies without prior preparation or labeling. This work lays the foundations for future developments in multiphoton microscopy as a method for measuring molecular order in intact biological media and opens the way to potential novel applications for detecting and studying the early stages of pathologies linked to molecular disorders.