Chemistry/Biochemistry
Session Topic:
Molecular Imaging
Chair:
Hervé Rigneault/Institut Fresnel CNRS - Mosaic group
Molecular imaging deals with the detection of molecular entities which are present in cell, tissues or on surfaces. Because the signal of such tiny emitters is very faint, dedicated approaches and techniques need to be implemented. Although it provides a nanometer resolution, the electronic microscope is unable to work on living samples. On the contrary, optical techniques are well adapted to work on living cells and tissues and have to exhibit dedicated characteristics such as:
-A high sensitivity: molecular concentrations found in biological signalling processes are often very low and require a high sensitivity (down to the single molecule level) together with a large optical magnification. It is also important to find an efficient and specific contrast mechanism to detect the molecules of interest.
-A high spatial and temporal resolving power: the cell volume exhibits a variety of sub-structures and one aims at localizing the molecular signal with the best accuracy, furthermore a good temporal resolution (s to ms) is needed to describe most of the biological dynamics.
-Cell innocuousness: Any relevant study should not perturb the cell and keep it in its natural physiological state.
Although local probe techniques are making progresses, they still exhibit limitations connected to the accurate monitoring of the distance between the probe and the soft biological sample. Optical techniques and especially far field microscopy are still nowadays the best compromise for sensitivity, spatial and temporal resolution, innocuousness and easiness of implementation. Although the fluorescence contrast is widely used in molecular imaging in bio and non bio sample, new techniques are arising that used the interaction of an ultra-short laser pulse with a molecular assembly.
In this session we will have two talks illustrating these new techniques:
Ms Sophie Brasselet from the ENS Cachan and will focus on optical techniques that are able to reveal order at a molecular scale. Second harmonic generation and two photons fluorescence combined with light polarization analysis will be used to study molecular order in various systems.
Mr Hideaki Kano from the University of Tokyo will present an optical technique that is able to build an image of the molecular bonds present in the sample. Known as CARS (Coherent Anti-stokes Raman Scattering), this innovative approach can work directly on unstained samples and is not subject to photo-bleaching.
These two examples illustrate how these new approaches are promising to study at a molecular scale the order, the diffusion in time and space and the interactions.