Publication

To study toroidal bubbles at our leisure, we trapped them within 3D-printed cages (using DLP) with openings small enough to prevent water from entering. We have shown that their resonant frequency is higher when the tori are thin, i.e. when their small radius becomes much smaller than their large radius. These bubbles can be assembled to produce original acoustic fields: for example in a long tunnel of rings

At the ocean level, we hypothesize that dolphins should already be aware of the acoustic properties of rings since they often emit pulsed sounds when making rings. In particular, they should be able to detect a “glissando” toward higher resonance frequencies when a ring enlarges and narrows during its ascent.

Reference
M. Alloul, B. Dollet, O. Stephan, E. Bossy, C. Quilliet, and P. Marmottant Acoustic resonance frequencies of underwater toroidal bubbles Physical Review Letters 129, 134501 (2022)

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The migration of cells in 3D media is a complex process and plays a key role in the development of cancers. During metastasis, cancer cells develop a strategy and a mode of migration adapted to their environment to invade other tissues.

In this study, we analyzed the migration of cancer cells with different metastatic potentials in various collagen matrices. The collagen fibers and the cell actin cytoskeleton were visualized simultaneously using the reflection and fluorescence imaging modes on a confocal microscope. The displacement fields of collagen fibers were determined using a home–made phase correlation algorithm applied to the reflection image stacks obtained in time. The analysis of the cell shape in parallel with the collagen fiber displacement showed the most invasive cells are characterized by a great diversity of shape. These cells produced the largest fiber displacements whatever the rigidity of the collagen gel. The detailed analysis of cell movements enhanced the fact that cancer cells were also able to exhibit different phenotypes (mesenchymal and amoeboid) according to their metastatic potential. We showed that cells can push and/or pull collagen fibers in order to deform collagen efficiently. The actin–rich regions were found to be correlated with the largest displacement fields and the correlation is enhanced in the case of most invasive cells.

Figure : 3D collagen fiber displacements around a migrating bladder cancer cell. The initial 3D cell shape is shown in grey. The vector length and the color indicate the displacement magnitude in µm. The x, y and z grids are in µm.

See online : Laforgue, L., Fertin, A., Usson, Y., Verdie C. & Laurent V. Efficient deformation mechanisms enable invasive cancer cells to migrate faster in 3D collagen networks. Sci Rep 12, 7867 (2022)

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We therefore proposed to combine FFS with photobleaching and demonstrated theoretically that, regardless of the initial distribution of individual fluorescent markers on the countable features, the brightness (measured by FFS) always decreases linearly, thus providing two results: the brightness of individual fluorescent markers and a parameter depending on the mean and variance of the distribution of these markers on the countable features. We experimentally demonstrated this new method using a streptavidin monolayer (acting as a host for biomimetic samples) to estimate the surface density of streptavidins and then the density of biotin molecules that bind to them. The density of the streptavidin monolayer estimated with our new method is in excellent agreement with completely independent ellipsometric spectroscopy measurements.

We present a new, self-calibrating method called pbFFS (for photobleaching fluctuation fluorescence spectroscopy) whose objective is to characterize molecules or particles labeled with an unknown distribution of fluorophores. Thanks to photobleaching, which acts as a control parameter, the pbFFS method provides information on the distribution of fluorescent labels and a reliable estimate of the density or absolute concentration of the molecules of interest. We fully demonstrate the principle of the pbFFS method theoretically and also implement it to measure the surface density of a monolayer of fluorescently labeled streptavidin molecules, which is used as a base layer to develop biomimetic systems. The surface density measured by pbFFS is consistent with the results of spectroscopic ellipsometry, a classical surface technique. However, pbFFS has two main advantages: it allows in situ characterization (no dedicated substrate is required) and can be applied to low masses of adsorbed molecules, which we demonstrate here by quantifying the density of biotin-Atto molecules that bind to the streptavidin layer. Finally, we also applied pbFFS to molecules diffusing in solution, in order to confirm the distribution of fluorescent markers found on the surface. In conclusion, pbFFS provides a set of tools to study molecules labeled with a variable number of fluorophores, with the aim of quantifying either the number of molecules or the distribution of fluorescent markers, the latter being particularly relevant for oligomerization studies.

See online : Combining Fluorescence Fluctuations and Photobleaching to Quantify Surface Density” Julius Sefkow-Werner, Elisa Migliorini, Catherine Picart, Dwiria Wahyuni, Irène Wang, and Antoine Delon Anal. Chem.

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Signal correlation is a fundamental operation for many imaging and location-based applications. In astronomy, interferometry techniques provide high resolution images from the correlation of signals received by different antennas or telescopes. Similarly, we can locate a radio transmitter by measuring the relative delays of signals received at different locations by correlation. However, the digital techniques that usually perform this operation are intrinsically limited by the sampling rate of the converters, as well as by the real-time processing capacity. In practice, digital correlation cannot handle radio signals with a bandwidth of more than a few hundred MHz. However, bandwidth is an important parameter, as it is synonymous with more flux in astronomy and increased resolution in the case of transmitter location. Researchers from the Laboratoire Interdisciplinaire de Physique (LIPhy, CNRS/UGA) and the Institut de Planétologie et d'Astrophysique de Grenoble (IPAG, CNRS/UGA) have developed a new concept of photonic architecture that calculates in real time the correlation function of radio signals in an analog way and is adapted to signals with a bandwidth between a few MHz and a few GHz. These results are published in the journal Optica.

Figure: Measurement of the time difference of arrival of radio frequency signals by photonic correlation. The signal whose spectrum is represented in (a) is transmitted by the Tx antenna (b). Two receiving antennas (Rx1 and Rx2) pick up the signal and send it to the analog optical correlator (b). The maximum of the correlation function gives the difference in signal propagation time between the transmitting antenna and the two receiving antennas. By moving Rx2 (in 1 inch steps), a translation of the correlation function is observed, due to the change in propagation time between the transmitter and Rx2 (c).
This concept is based on the so-called multi-heterodyne interferometry and it consists in giving in real time the completeness of the correlation function of two signals by calculating simultaneously, for more than 200 values of relative delays, the cross-correlation coefficients between the signals. To do this, the radio signals are transferred to the optical domain and then sent through a pair of loops whose function is to produce replicas of the input signals that are shifted both in time and in frequency. The main contribution of the method is this double loop architecture which allows the calculation of the correlation function to be parallelized. The time step of the correlator, which corresponds to the difference in travel times in the two loops, is adjusted from a few nanoseconds to a few picoseconds to process signals with a bandwidth ranging from MHz to GHz. The researchers applied this architecture to the localization of radio frequency transmitters by time difference of arrival (figure) and obtained an accuracy close to 10 ps for an integration time of 100 ms.
It remains to characterize the performances of this architecture to apply it to the real-time localization of transmitters, wifi and cell phones for example. In astronomy, a preliminary experiment of imaging the sun by radio interferometry at 10 GHz will be carried out at IPAG in order to evaluate the interest of this technique for imaging.

See online : Multi-delay photonic correlator for wideband RF signal processing. G. Bourdarot, J.-P. Berger, H. Guillet de Chatellus ;Optica, paru le 24 mars 2022.

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An international consortium including LIPhy researchers has developed a new technology to make these peptides photoactivatable, thus allowing precise spatiotemporal control of neuronal ion channels associated with excitability. This technology opens the door to new opportunities for translational research and therapeutic applications using light.

See online : In vivo spatiotemporal control of voltage-dependent ion channels using photoactivatable peptide toxins. Montnach J, Blömer LA, et al, Nat Commun. 2022 Jan 20;13(1):417.

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