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Adaptive optics for quantitative confocal microscopy

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The resolution of fluorescence microscopy is often limited by the aberrations introduced by the biological sample when imaging deep into thick tissues. Indeed, the sample distorts the incident and radiated fields, thereby degrading the image formation. It is possible, however, as what is done in astronomy (where aberrations are due to atmospheric turbulences), to correct the wave front, using, for example, a deformable mirror : this is the principle of Adaptive Optics (AO).

A new approach, adapted to confocal microscopy, has been proposed at the Interdisciplinary Physics Laboratory (LIPhy) and Institut for Advanced Biosciences (IAB) from 2011. While, in general, certain characteristics of the image (such as the intensity or the contrast) are used to measure the impact of the deformation of the wave front, the new strategy implementation takes advantage of the temporal fluctuations of fluorescence due to the small number of molecules diffusing through the confocal volume. Indeed, it is possible to calculate, from these fluctuations, quantities such as the average number of molecules in the confocal volume, or their brightness (that is to say, the signal per molecule)1. It should be mentioned that most of the time confocal microscopy of biological living specimens does not allow direct measurement of the wave front. In fact, measuring a quantity such as brightness is equivalent to measure the signal from a single guide star and thus allows access to the Strehl ratio. This principle has already been demonstrated in the frame of a former ANR (National Agency for Research) Emergence project (2012- mid 2014) and led to several publications about biological applications and one patent2,3,4.
The Confobright projects aims first at setting-up on the IAB platform a quantitative confocal microscope equipped to perform fluorescence fluctuation measurements with an adaptive optics add-on. In contrast to the initial home-made system built at the LIPhy laboratory, the IAB prototype will be based on commercial only solutions. The quantitative confocal microscope will be provided by a company with whom we are collaborating, while the choice of the adaptive optics add-on is currently under investigation. The software developments necessary to drive the deformable mirror will be done with the technical support of the microscopy company. Along with these technical developments, a series of biological applications will be investigated on the IAB platform to assess and optimize the performances of the AO-quantitative confocal microscope in various experimental conditions.

The project will run for 18 months, with the financial support of the Technology transfer & start-up building company of Grenoble Alpes.
We are seeking for a talented engineer and/or PhD, with a strong experience in advanced microscopy and willing to work at the interface between physics and biology. Knowledges in confocal microscopy, adaptive optics, photon correlation and control software are especially welcome. The position is available from January-February 2017.

(1) C.-E. Leroux et al., Adaptive Optics for Fluorescence Correlation Spectroscopy, Opt. Exp., 19, 26839-26849 (2011).
(2) C.-E. Leroux et al., Correction of cell-induced optical aberrations in a fluorescence fluctuation microscope, Opt. Let. 38, 2401-2403 (2013)
(3) C.-E. Leroux et al., Fluorescent correlation spectroscopy measurements with adaptive optics in the intercellular space of spheroids, Bio. Opt. Exp. 5, 3730 (2014)
(4) A. Delon, C.-E. Leroux et A. Grichine, Adaptive optics device using fluorescent signal fluctuations, US patent application No. 61/737427

Adaptative Optics