More Chemistry...
MORE CHEMISTRY ...
UCNP
Emission of high energy light (Visible or UV) after absorption of low energy photons (Near Infra Red) seems to go against Nature's laws. This is however observed for some crystals such as inorganic matrices doped with lanthanide ions. This spectacular feature is bound to the intrinsic long lived excited states of these metallic ions and to the regular spacing of their energy levels. To maximize the (poor) quantum yield, special care has to be taken to attain the proper crystal host phase. On the other way round, for biological applications, the nanocrystal' size control is mandatory. To achieve this goal we will participate to the design of a heating device to monitor the size of the particles during their growth.
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PHOTOCHROMIC DYES
Under light exposure, certain dyes undergo a reversible transformation that modifies their colour. The most spectacular one switch from colorless to colored (positive photochromism), other will be bleached. when the dye return spontaneously in the dark tio its original stable state it is called a T-photochrom, such as in sunglasses
SUPER-RESOLUTION
Whichever the optical technique used, there is a limit in the observation of details in a recorded image: the ability to distinguish two features in close vicinity. This limit of resolution is due to diffraction that was demonstrated by Ernst Abbe in 1873. Generally, the resolution limit of a fluorescent microscope is around 250 nm.
For a long time, this limit was considered to be insurmountable. Considerable investigations in the 90’s led to new techniques collectively termed super-resolution techniques, bypassing this barrier, that were crowned by the 2014 Nobel Prize.
Two families of super-resolution methodologies can be distinguished:
-the physical "Deterministic way", based on patterned illumination spectroscopy (ex: STimulated Emission Depletion STED),
-and the stochastic approach (ex: Single-Molecule Localization Microscopy (SMLM), Super-resolution Optical Fluctuation Imaging (SOFI)).
In the frame of this project, we focused on the stochastic approach, where the resolution is achieved thanks to single molecule localization of blinking probes over successives temporal acquisitions (around 5k-10k frames).
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