We propose a simple microfluidic device able to separate submicron particles (critical size ∼0.1 μm) from a complex sample with no filter (minimum channel dimension being 5 μm) by hydrodynamic filtration. A model taking into account the actual velocity profile and hydrodynamic resistances enables prediction of the chip sorting properties for any geometry. Two design families are studied to obtain (i) small sizes within minutes (low-aspect ratio, two-level chip) and (ii) micron-sized sorting with a μL flow rate (3D architecture based on lamination). We obtain quantitative agreement of sorting performances both with experiments and with numerical solving, and determine the limits of the approach. We therefore demonstrate a passive, filter-less sub-micron size sorting with a simple, robust, and easy to fabricate design.
International audienceImpedance spectroscopy has gained interest for the quantitative detection of specific cells mainly due to a label-free detection and their miniaturization capability required for integration on chip and development of point-of-care diagnostics. In this paper, we report the study of impedimetric microfluidic devices with improved sensitivity targeting the immuno-detection of cells. The sensitivity of our system was evaluated in terms of the capacity of the electrodes to trap monocytes by immune-reaction with CD14 antibody immobilized on micro-electrode surface. All measurements were performed in faradic mode using a redox probe. The sensitivity was evaluated as a function of the impedance increase recorded at 100 Hz caused by the insulating character of the cell trapped on electrodes. Analyses first confirmed that the sensing performances were significantly improved by using microfluidic. This increase could originate from an increase in the probability of cell trapping and a better organization of cells on the electrode due to the laminar flow. The great sensitivity was recorded with interdigitated electrodes for which the influence of the gap value was evaluated. The maximum sensitivity was reached with the smallest inter-electrodes gap tested (50 µm). This performance was in part attributed to the redox cycling taking place between neighboring fingers that was strongly affected when cells were trapped on the electrodes edges. Furthermore we also demonstrate that the slice of cell concentration for which the sensitivity is maximized is correlated to the area of electrodes. Moreover, the smallest area of interdigitated electrode (0.1 mm length) allowed the detection of as low as 5 cells per m
Mating-type switching in the budding yeast Saccharomyces cerevisiae relies on the Sir protein complex to silence HML and HMR, the two loci containing copies of the alleles of the mating type locus, MAT. Sir-based transcriptional silencing has been considered locus-specific, but the recent discovery of rare and transient escapes from silencing at HMLα2 with a sensitive assay called to question if these events extend to the whole locus. Adapting the same assay, we measured that transient silencing failures at HML were more frequent for the α2 gene than α1, similarly to their expression level in unsilenced cells. By coupling a mating assay, at HML we found that one of the two genes at that locus can be transiently expressed while the other gene is maintained silent. Thus transient silencing loss can be a property of the gene rather than the locus. Cells lacking the SIR1 gene experience epigenetic bistability at HML and HMR. Our previous result led us to ask if HML could allow for two independent epigenetic states within the locus in a sir1Δ mutant. A simple construct using a double fluorescent reporter at HMLα1 and HMLα2 ruled out this possibility. Each HML locus displayed a single epigenetic state. We revisited the question of the correlation between the states of two HML loci in diploid cells, and showed they were independent. Finally, we determined the relative strength of gene repression achieved by Sir-based silencing with that achieved by the a1-α2 repressor.
Periodic arrays of micro-or nano-pillars constitute solid state matrices with excellent properties for DNA size separation. Nanofabrication technologies offer many solutions to tailor the geometry of obstacle arrays, yet most studies have been conducted with cylinders arranged in hexagonal lattices. In this report, we investigate the dynamics of single DNA collision with elliptical nanoposts using hydrodynamic actuation.Our data shows that the asymmetry of the obstacles has minor effect on unhooking dynamics, and thus confirms recent predictions obtained by Brownian dynamics simulations. In addition, we show that the disengagement dynamics are correctly predicted by models of electrophoresis, and propose that this consistency is associated to the confinement in slit-like channels. We finally conclude that elliptical posts are expected to marginally improve the performances of separation devices.Size separation of DNA molecules with electrophoresis is a key process of molecular biology, which has been widely investigated over decades [1]. Separation cannot be performed in free solution [2], requiring the use of matrices to achieve size-dependent DNA mobilities. Slab gels are the most common separation matrices, but optimal performances have been reached with capillaries of hundreds of µm in diameter filled with concentrated polymer solutions. This technology features excellent physical properties associated to rapid heat dissipation and reduction of convection [3], and the chemical composition of polymer solutions has been tailored to enhance the resolution of separation experiments, which now reach base-pair (bp) resolution for fragments up to ~500-1000 bp [4]. Despite these successes, the nanoscale arrangement of polymer solutions is intrinsically disordered, making it difficult to precisely control the migration of DNA at the molecular level. Therefore Volkmuth and Austin proposed to use micro or nanofabricated solid state artificial matrices for DNA separation [5]. These systems consist of arrays of posts etched in glass or silicon with exquisite control over their size, spacing, and shape from the nano to the millimeter scale. This approach showed impressive results for long DNA chains of ~100.10 3 base pairs (100 kbp) [6] that were separated in tens of seconds in comparison to hours otherwise [7]. For shorter DNA fragments, artificial matrices of nanoposts of ~200 nm in radius have been devised, also showing exquisite performances [8].Machining technologies offer many choices for the design of the matrix, yet hexagonal arrays of cylindrical obstacles have been predominantly characterized in the literature [9]. The idea of using asymmetric obstacles to separate biomolecules has nevertheless been documented in the context of e.g.Brownian ratchet devices [10], which enable to perform spatial separations of DNA based on the size dependence of its diffusion coefficient [11]. Dense and asymmetric obstacles have also been incorporated into artificial matrices to test their separation power [12], and it was...
This study demonstrates the integration of a multilevel magnetophoretic lab on chip: combining 3D fluid engineering and localized magnetic actuation enables the full integration of a cell tagging and magnetic separation device. A system performing magnetic handling of beads at cell resolution was also devised based on the same technologies.
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