We present an optical realization of a thermal ratchet. Directed motion Brownian particles in water is induced by modulating time spatially periodic but asymmetric potential. The net drift shows maximum as function the modulation period. experimental results agree with simple theoretical model based on diffusion.

We report results of a micromanipulation study single double-helical DNA molecules at forces up to 150 pN. Depending on whether the winding is allowed relax, or held fixed, qualitatively different structural transitions are observed. By studying as function structures underlying them characterized; this allows us first estimate $S\ensuremath{-}\mathrm{DNA}$ helicity. A model introduced describe these transitions; in addition $B\ensuremath{-}\mathrm{DNA}$, we find that four states needed experiments.

High resolution optical microscopy is essential in neuroscience but suffers from scattering biological tissues and therefore grants access to superficial brain layers only. Recently developed techniques use scattered photons for imaging by exploiting angular correlations transmitted light could potentially increase depths. But those ('angular memory effect') are of a very short range should theoretically be only present behind not inside media. From measurements on neural complementary...

Two-photon laser scanning microscopy (2PLSM) is an important tool for in vivo tissue imaging with sub-cellular resolution, but the penetration depth of current systems potentially limited by sample-induced optical aberrations. To quantify these, we measured refractive index n' somatosensory cortex 7 rats using defocus optimization full-field coherence tomography (ff-OCT). We found to be independent or rat age. From these measurements, calculated that two-photon beyond 200 µm into spherical...

We describe a fast continuous optimization wavefront shaping system able to focus light through dynamic scattering media. A micro-electro-mechanical system-based spatial modulator, photodetector, and field programmable gate array electronics are combined implement of with single-mode rate 4.1 kHz. The performances demonstrated by focusing colloidal solutions TiO2 particles in glycerol tunable temporal stability.

Most genetic regulatory mechanisms involve protein-DNA interactions. In these processes, the classical Watson-Crick DNA structure sometimes is distorted severely, which in turn enables precise recognition of specific sites by protein. Despite its key importance, very little known about such deformation processes. To address this general question, we have studied a model system, namely, RecA binding to double-stranded DNA. Results from micromanipulation experiments indicate that binds...

Rheological experiments were carried out on aqueous dispersions of cetyltrimethylammoniumhydroxynaphthalenecarboxylate (CTAHNC) as a function temperature. The results indicate the formation very long elongated wormlike micelles at temperatures higher than about 50 °C, conferring to system high viscosity. This behavior is explained by combined effect large end cap energy and low ionization degree resulting from strong binding weakly soluble counterions. At lower temperature surfactant forms...

In the neocortex, neuronal selectivities for multiple sensorimotor modalities are often distributed in topographical maps thought to emerge during a restricted period early postnatal development. Rodent barrel cortex contains somatotopic map vibrissa identity, but existence of representing other tactile features has not been clearly demonstrated. We addressed issue rat an intrabarrel movement direction using vivo two-photon imaging. discovered that emergence occurs long after all known...

We create tailored microstructures, consisting of complexes lipid membranes with self-assembled biopolymer shells, to study the fundamental properties and interactions these basic components living cells. measure mechanical response artificial structures at micrometer scale, using optical tweezers single-particle tracking. These systems exhibit rich dynamics that illustrate viscoelastic character quasi-two-dimensional network. present a theoretical model relating rheological observed dynamics.

In a commonly used motility assay, cytoskeletal filaments are observed as they glide over surface coated with motor proteins. Defects in the motion frequently interrupt flow of filaments. Examination one such defect, which filament adopts spiral form and rotates about fixed point, provides simple measure force exerted by We demonstrate universality this approach estimating elementary forces both myosin kinesin.

Myelin sheath disruption is responsible for multiple neuropathies in the central and peripheral nervous system. imaging has thus become an important diagnosis tool. However, vivo been limited to either low-resolution techniques unable resolve individual fibers or low-penetration of single fibers, which cannot provide quantitative information about large volumes tissue, as required diagnostic purposes. Here, we perform myelin without labeling at micron-scale resolution with >300-μm...

We designed Calcium Rubies, a family of functionalizable BAPTA-based red-fluorescent calcium (Ca(2+)) indicators as new tools for biological Ca(2+) imaging. The specificity this Ca(2+)-indicator is its side arm, attached on the ethylene glycol bridge that allows coupling indicator to various groups while leaving open possibility aromatic substitutions BAPTA core tuning Ca(2+)-binding affinity. Using we now synthesize and characterize three different CaRubies with affinities between 3 22 μM....

Acousto-optic deflection (AOD) devices offer unprecedented fast control of the entire spatial structure light beams, most notably their phase. AOD modulation ultra-short laser pulses, however, is not straightforward to implement because intrinsic chromatic dispersion and non-stationarity acousto-optic diffraction. While schemes exist compensate dispersion, remains an obstacle. In this work we demonstrate efficient modulator for stable phase using time-locked generation frequency-modulated...

In living cells, cytoskeletal filaments interact with the plasma membrane to form structures that play a key role in cell shape and mechanical properties. To study interaction between these basic components, we designed an vitro self-assembled network of actin attached outer surface giant unilamellar vesicles. Optical tweezers single-particle tracking experiments are used rich dynamics actin-coated membranes (ACM). We show microrheology studies can be carried out on such individual...

Combining optical microscopy and atomic force microscopy, a complete characterization of Langmuir-Blodgett bilayers made arachidic acid has been performed. At macroscopic scales, both techniques can be used to control the homogeneity transferred films. By roughness thickness could determined. These are compatible with normal orientation fully extended aliphatic chains respect substrate. Molecular-resolution images give first direct experimental evidence for presence pairs dislocations in...

Langmuir-Blodgett films of barium arachidate have been studied on both macroscopic and microscopic scales by atomic force microscopy. As prepared, the exhibit a disordered hexagonal structure; molecularly resolved images in direct space establish connection between extent positional order presence defects such as dislocations. Upon heating, reorganize into more condensed state with centered rectangular crystallographic arrangement; this new long-range unusual structural features, height...

The mechanical properties of composite membranes obtained by self-assembly actin filaments with giant fluid vesicles are studied micromanipulation optical tweezers. These complexes exhibit typical features a solid shell, including finite in-plane shear elastic modulus $(\ensuremath{\sim}{10}^{\ensuremath{-}6}\phantom{\rule{0ex}{0ex}}\mathrm{N}/\mathrm{m})$. A buckling instability is observed when localized force the order 0.5 pN applied perpendicular to membrane plane. Although predicted for...

We report a micelle−vesicle transition induced by the addition of neutral cosurfactant, hexanol, into wormlike micellar solution gemini cationic surfactant. This was investigated with rheology measurements as well direct imaging techniques. It observed cryo transmission electron microscopy that micelles first become elongated an increase which increases viscosity. As hexanol concentration is increased, another more fluid phase appears, where are highly branched and coexist small vesicles....

The buckling of a two-dimensional polymer network at the air-water interface has been evidenced by grazing incidence x-ray scattering. A comprehensive description inhomogeneous octadecyltrichlorosilane polymerized film was obtained atomic force microscopy and scattering measurements. occurs with characteristic wavelength \ensuremath{\simeq}10 \ensuremath{\mu}m.

We have studied silanated-silica surfaces concurrently by Atomic-Force Microscopy and contact angle measurements. observations evidenced two types of defects at the nanometer scale within silane layers which were detected neither nor hysteresis In contrast, in case incomplete layers, these latter measurements exhibited a high sensitivity to surface coverage as soon it becomes lower than critical value. Chemical modifications tip been performed adhesion forces are reported.

may come from teaching and research institutions in France or abroad, public private centers.L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques niveau recherche, publiés ou non, émanant des établissements d'enseignement recherche français étrangers, laboratoires publics privés.A spatio-temporally compensated acousto-optic scanner for two-photon microscopy providing large field of view

Nonlinear fluorescence microscopy promotes in-vivo optical imaging of cellular structure at diffraction-limited resolution deep inside scattering biological tissues. Active compensation tissue-induced aberrations and light through adaptive wavefront correction further extends the accessible depth by restoring high large depth. However, those corrections are only valid over a very limited field view within angular memory effect. To overcome this limitation, we introduce an acousto-optic...