Accelerated Transport of Particles in Confined Channels with a High Roughness Amplitude.

We investigate the pressure-driven transport of particles 200 or 300 nm in diameter in shallow microfluidic channels ∼1 μm in height with a bottom wall characterized by a high roughness amplitude of ∼100 nm. This study starts with the description of an assay to generate cracks in hydrophilic thin polymer films together with a structural characterization of these corrugations. Microfluidic chips of variable height are then assembled on top of these rough surfaces, and the transport of particles is assessed by measuring the velocity distribution function for a set of pressure drops.

DNA separation and enrichment using electro-hydrodynamic bidirectional flows in viscoelastic liquids.

DNA size separation followed by purification and enrichment constitute essential operations for genetic engineering. These processes are mostly carried out using DNA electrophoresis in gels or in polymer solutions, a well-established yet lengthy technique which has been notably improved using Lab-on-Chip technologies. So far, innovations for DNA separation or enrichment have been mostly undertaken separately, and we present an approach that allows us to perform these two processes simultaneously for DNA fragments spanning 0.

Metrology of confined flows using wide field nanoparticle velocimetry.

The manipulation of fluids in micro/nanofabricated systems opens new avenues to engineer the transport of matter at the molecular level. Yet the number of methods for the in situ characterization of fluid flows in shallow channels is limited. Here we establish a simple method called nanoparticle velocimetry distribution analysis (NVDA) that relies on wide field microscopy to measure the flow rate and channel height based on the fitting of particle velocity distributions along and across the flow direction.

Relevance and limitations of crowding, fractal, and polymer models to describe nuclear architecture.

Chromosome architecture plays an essential role for all nuclear functions, and its physical description has attracted considerable interest over the last few years among the biophysics community. These researches at the frontiers of physics and biology have been stimulated by the demand for quantitative analysis of molecular biology experiments, which provide comprehensive data on chromosome folding, or of live cell imaging experiments that enable researchers to visualize selected chromosome loci in living or fixed cells. In this review our goal is to survey several nonmutually exclusive models that have emerged to describe the folding of DNA in the nucleus, the dynamics of proteins in the nucleoplasm, or the movements of chromosome loci.

High-throughput chromatin motion tracking in living yeast reveals the flexibility of the fiber throughout the genome.

Chromosome dynamics are recognized to be intimately linked to genomic transactions, yet the physical principles governing spatial fluctuations of chromatin are still a matter of debate. Using high-throughput single-particle tracking, we recorded the movements of nine fluorescently labeled chromosome loci located on chromosomes III, IV, XII, and XIV of Saccharomyces cerevisiae over an extended temporal range spanning more than four orders of magnitude (10(-2)-10(3) sec). Spatial fluctuations appear to be characterized by an anomalous diffusive behavior, which is homogeneous in the time domain, for all sites analyzed.

Mapping the local organization of cell membranes using excitation-polarization-resolved confocal fluorescence microscopy.

Fluorescence anisotropy and linear dichroism imaging have been widely used for imaging biomolecular orientational distributions in protein aggregates, fibrillar structures of cells, and cell membranes. However, these techniques do not give access to complete orientational order information in a whole image, because their use is limited to parts of the sample where the average orientation of molecules is known a priori. Fluorescence anisotropy is also highly sensitive to depolarization mechanisms such as those induced by fluorescence energy transfer.

An atomic force microscopy analysis of yeast mutants defective in cell wall architecture.

Yeast cells are surrounded by a thick cell wall, the composition and structure of which have been characterized by biochemical and genetic methods. In this study, we used atomic force microscopy (AFM) to visualize the cell surface topography and to determine cell wall nanomechanical properties of yeast mutants defective in cell wall architecture. While all mutants investigated showed some alteration in cell surface topography, this alteration was particularly salient in mutants defective in beta-glucan elongation (gas1), chitin synthesis (chs3) and cross-linkages between chitin and beta-glucan (crh1crh2).