In nanometer-sized apertures with charged surfaces, the extension of the electrical double layer results in the electrostatic exclusion of co-ions and enrichment in counterions, which affects the permselectivity of such structures. A modeling of this phenomenon is proposed and is compared with quantitative measurements of the ionic permeability change of a Pyrex nanoslit at low ionic strength. The comparison of experimental results with theoretical predictions justifies that electrostatic forces are the governing forces in nanofluidics.

We report on the systematic investigation of electropreconcentration phenomena in hybrid micro/nanofluidic devices. The competition between the electroosmotic dragging force and the highly nonlinear electrophoretic forces induced by the polarization effect is responsible for four preconcentration regimes within such structures that can arise at both cathodic and anodic sides of the nanochannel. Numerical calculations on the spatiotemporal concentration of charged molecules confirm such a classification, showing a general agreement with the reported experimental data at low and moderate ionic strengths. The results also suggest that both the mobility and the valence of the species of interest are important parameters in the determination of the preconcentration rates.

One major advantage of using genetically tractable model organisms such as the fission yeast Schizosaccharomyces pombe is the ability to construct temperature-sensitive mutations in a gene. The resulting gene product or protein behaves as wildtype at permissive temperatures. At non-permissive or restrictive temperatures the protein becomes unstable and some or all of its functions are abrogated. The protein regains its function when returning to a permissive temperature. In principle, temperature-sensitive mutation enables precise temporal control of protein activity when coupled to a fast temperature controller. Current commercial temperature control devices do not have fast switching capability over a wide range of temperatures, making repeated temperature changes impossible or impractical at the cellular timescale of seconds or minutes. Microfabrication using soft-lithography is emerging as a powerful tool for cell biological research. We present here a simple disposable polydimethylsiloxane (PDMS) based microfluidic device capable of reversibly switching between 5 °C and 45 °C in less than 10 s. This device allows high-resolution live cell imaging with an oil immersion objective lens. We demonstrate the utility of this device for studying microtubule dynamics throughout the cell cycle.

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We investigate the preconcentration profiles of a fluorescein and bovine serum albumin derivatized with this fluorescent tag in a microfluidic chip bearing a nanoslit. A new preconcentration method in which a hydrodynamic pressure is added to both electroosmotic and electrophoretic contributions is proposed to monitor the location of the preconcentration frontline. A simple predictive model of this pressure-assisted electropreconcentration is proposed for the evolution of the flow profile along this micro/nano/microfluidic structure. We show with a small analyte such as fluorescein that the additional hydrostatic pressure mode enables to stabilize the concentration polarization (CP) effect, resulting in better control of the cathodic focusing (CF) peak. For BSA (bovine serum albumin), we exhibit that the variation of the hydrodynamic pressure can have an even more drastic effect on the preconcentration. We show that, depending on this hydrodynamic pressure, the preconcentration can be chosen, either in the cathodic side or in the anodic one. For the first time, we prove here that both anodic focusing (AF) and cathodic focusing (CF) regimes can be reached in the same structures. These results also open new routes for the detection and the quantification of low abundance biomarkers.