[Show abstract][Hide abstract] ABSTRACT: To determine the octanol–water partition coefficient (log Kow or log D), a microfluidic method is developed to reduce time and coast of analyze. A double Y serpentine microfluidic chip is fabricated used soft lithography facilities. To generate a biphasic parallel flow, hydrophilic microchannels walls are generated by oxygen plasma treatment. Epifluorescence microscopy is used to measure the intensity of fluorescence molecules in microchannel. Using microfluidic parallel diluter this intensity show a strong linear correlation with molecule concentration in solution. The equilibrium between phases is reached in less than 5 s. To validate this microsystem, we have determined the log D of fluorescein natrium molecule. The obtained results compare well with previous measurements using traditional shake-flask or microfluidic drops flow methods, with a relative difference to the literature less than 3%. Rapid microfluidic partition coefficient determination is useful for studying liquid–liquid partition of organic pollutant.
[Show abstract][Hide abstract] ABSTRACT: This paper reports the use of a recent composite material, noted hereafter i-PDMS, made of carbonyl iron microparticles mixed in a PolyDiMethylSiloxane (PDMS) matrix, for magnetophoretic functions such as capture and separation of magnetic species. We demonstrated that this composite which combine the advantages of both components, can locally generate high gradients of magnetic field when placed between two permanent magnets. After evaluating the magnetic susceptibility of the material as a function of the doping ratio, we investigated the molding resolution offered by i-PDMS to obtain microstructures of various sizes and shapes. Then, we implemented 500 μm i-PDMS microstructures in a microfluidic channel and studied the influence of flow rate on the deviation and trapping of superparamagnetic beads flowing at the neighborhood of the composite material. We characterized the attraction of the magnetic composite by measuring the distance from the i-PDMS microstructure, at which the beads are either deviated or captured. Finally, we demonstrated the interest of i-PDMS to perform magnetophoretic functions in microsystems for biological applications by performing capture of magnetically labeled cells.
[Show abstract][Hide abstract] ABSTRACT: Microfluidic technology has opened new possibilities for the crystallization of biological macromolecules during the past decade. Microfluidic systems offer numerous advantages over conventional crystal growth methods. They enable easy handling of nanovolumes of solutions, extreme miniaturization, and parallelization of crystallization assays, especially for high throughput screening applications. Our goal was to design a versatile, low cost, and easy-to-use crystallization chip based on counter-diffusion that is compatible with on-chip crystallographic characterization. The ChipX is a microfluidic chip made of cyclic olefin copolymer. It was used to grow crystals of biomolecules and perform complete X-ray diffraction analyses on synchrotron sources. Our results demonstrate that accurate crystallographic data can be collected at room temperature directly from ChipX microfluidic devices for both experimental SAD phasing and structure refinement.
[Show abstract][Hide abstract] ABSTRACT: This paper demonstrates the potential use of a new microfluidic device embedding thick electrodes for cell lysis and cell separation applications. The system consists of a microfluidic channel featuring conductive walls made of a polydimethylsiloxane (PDMS) matrix mixed with carbon nanoparticles. Cell lysis was performed electrically by applying square pulses across the channel width, which was monitored by fluorimetry. Lysed and unlysed cells showed different dielectrophoretic behavior under appropriate experimental conditions, which suggests that the developed device is suitable to perform both cell lysis and subsequent sorting of viable and dead cells.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:6281-4.
[Show abstract][Hide abstract] ABSTRACT: We have developed a method for studying cellular adhesion by using a custom-designed microfluidic device with parallel non-connected tapered channels. The design enables investigation of cellular responses to a large range of shear stress (ratio of 25) with a single input flow-rate. For each shear stress, a large number of cells are analyzed (500-1500 cells), providing statistically relevant data within a single experiment. Besides adhesion strength measurements, the microsystem presented in this paper enables in-depth analysis of cell detachment kinetics by real-time videomicroscopy. It offers the possibility to analyze adhesion-associated processes, such as migration or cell shape change, within the same experiment. To show the versatility of our device, we examined quantitatively cell adhesion by analyzing kinetics, adhesive strength and migration behaviour or cell shape modifications of the unicellular model cell organism Dictyostelium discoideum at 21 °C and of the human breast cancer cell line MDA-MB-231 at 37 °C. For both cell types, we found that the threshold stresses, which are necessary to detach the cells, follow lognormal distributions, and that the detachment process follows first order kinetics. In addition, for particular conditions' cells are found to exhibit similar adhesion threshold stresses, but very different detachment kinetics, revealing the importance of dynamics analysis to fully describe cell adhesion. With its rapid implementation and potential for parallel sample processing, such microsystem offers a highly controllable platform for exploring cell adhesion characteristics in a large set of environmental conditions and cell types, and could have wide applications across cell biology, tissue engineering, and cell screening.
[Show abstract][Hide abstract] ABSTRACT: This paper reports on the integration of thick carbon-polydimethylsiloxane (C-PDMS) electrodes in microfluidic systems for electrokinetic operations. The C-PDMS material, obtained by mixing carbon nanopowder and PDMS, preserves PDMS processing properties such as O2 plasma activation and soft-lithography patternability in thick or 3D electrodes. Conductivity in the order of 10 S m−1 was reached for a carbon concentration of 25 wt%. To evaluate the adhesion between PDMS and C-PDMS, we prepared bi-material strips and carried out a manual pull test. The cohesion and robustness of C-PDMS were also evaluated by applying a large range of electric field conditions from dc to ac (300 kHz). No damage to the electrodes or release of carbon was noticed. The use of such a material for electrokinetic manipulation was validated on polystyrene particles and cells. Here, we demonstrate that C-PDMS seems to be a valuable technological solution for electrokinetic in microfluidic and particularly for biological applications such as cell electrofusion, lysis and trapping, which are favored by uniform lateral electric fields across the microchannel section.
Journal of Micromechanics and Microengineering 08/2011; 21(9):095013. · 1.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents an alternative approach to create low-cost and patternable carbon electrodes suitable for microfluidic devices. The fabrication and the electrochemical performances of electrodes made of Polydimethylsiloxane doped with commercially available carbon black (C-PDMS) are described. Conductivity and electrochemical measurements performed on various carbon to PDMS ratios showed that electrodes with suitable electrochemical properties were obtained with a ratio of 25 %.
[Show abstract][Hide abstract] ABSTRACT: The combination of microfluidic and electrochemistry for the generation of surface anisotropy of functionalized pyrrole is described. By using co-electropolymerization of pyrrole and pyrrole-biotin in a microfluidic environment, we have created a surface density gradient of pyrrole-biotin on gold electrodes as revealed by fluorescence. The combination of fast electropolymerization and microfluidic allows the transfer of a local volume anisotropy to a surface anisotropy with a tuneable slope of the gradient.
[Show abstract][Hide abstract] ABSTRACT: The objective of this work was to develop and characterize a poly(dimethylsiloxane) device with an integrated active cooling function able to carry out capillary electrophoresis separations. Polymer-based microdevices are indispensable to recent advances in biomedical analysis. In particular, they have been applied to many microfluidic platforms owing to their low cost, ease of fabrication, and versatility in preparing complex microstructures. However, when applied to capillary electrophoresis separations, polymer microfluidic structures present an inherent disadvantage compared to glass and Si structures; they have a lower thermal conductivity than glass and Si. Although miniaturized devices allow operation at high electric fields, they face separation efficiency limitations due to Joule heating. There is, therefore, a strong need of developing capillary electrophoresis microfluidic structures with active cooling in order to operate at a higher electric field and potentially increase separation efficiency in these microdevices. A poly(dimethylsiloxane)/glass hybrid microfluidic capillary electrophoresis system is presented, where Joule heating was minimized by using an integrated active cooling function. Two poly(dimethylsiloxane) slabs with embedded microfluidic structures were irreversibly sealed on both sides of a thin glass slide. The top poly(dimethylsiloxane) slab was used to carry out capillary electrophoresis separations, whereas the bottom poly(dimethylsiloxane) slab was employed to cool down the buffer solution used during the capillary electrophoresis separation. As demonstrated on current versus voltage plots and on capillary electrophoresis electropherograms, capillary electrophoresis separation was able to be operated at a higher electric field when using the cooling function. The cooling rate was adjustable by varying the flow rate and the initial temperature of the liquid flowing in the cooling microfluidic structure.
Experimental Heat Transfer 01/2010; 23(1):63-72. · 0.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Simulation and experimental data are combined to optimize the electrode geometry of a membraneless laminar flow glucose biofuel cell. The design of the cell is based on a Y-shaped microfluidic channel that exploits the laminar flow of fluids. Glucose is oxidized by the glucose oxidase enzyme at the anode whereas oxygen is reduced by the laccase enzyme at the cathode. The energy output level of the microfluidic biofuel cell is limited by the reaction-depletion boundary layer at the electrode surfaces. To optimize the electrochemical characteristics of the device, our approach involves the reduction of both electrode length and spacing between anode and cathode in the microchannel. Computational fluids dynamics and electrochemical measurements show that the current density and power density are 3 times higher by decreasing the electrode length from 10 to 0.5 mm. The device delivers a power density of 0.33 mW cm−2 for a cell voltage of 0.22 V in buffered solutions at 300 μL min−1 flow rate. Moreover, the electrical performances are increased by generating up to 0.55 mW cm−2 for a cell voltage of 0.3 V when ohmic losses in the electrolyte are decreased by reducing the distance between cathode and anode in the microchannel.
[Show abstract][Hide abstract] ABSTRACT: A microfluidic glucose/O2 biofuel cell, delivering electrical power, is developped based on both laminar flow and biological enzyme strategies. The device consists of a Y-shaped microfluidic channel in which fuel and oxidant streams flow laminarly in parallel at gold electrode surfaces without convective mixing. At the anode, the glucose is oxidized by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in presence of specific redox mediators. Such cell design protects the anode from interfering parasite reaction of O2 at the anode and works with different streams of oxidant and fuel for optimal operation of the enzymes. The dependence of pH and nature of mediator on the current is evaluated in order to determine the optimum conditions to high current densities. The maximum power density delivered by the assembled biofuel cell reaches 70 mW·cm−2 at 0.28 V with 10 mM glucose at 23 °C. The microfluidic approach reported here demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O2 biofuel cell device.
[Show abstract][Hide abstract] ABSTRACT: Microfluidic devices were designed to perform on micromoles of biological macromolecules and viruses the search and the optimization of crystallization conditions by counter-diffusion, as well as the on-chip analysis of crystals by X-ray diffraction. Chips composed of microchannels were fabricated in poly-dimethylsiloxane (PDMS), poly-methyl-methacrylate (PMMA) and cyclo-olefin-copolymer (COC) by three distinct methods, namely replica casting, laser ablation and hot embossing. The geometry of the channels was chosen to ensure that crystallization occurs in a convection-free environment. The transparency of the materials is compatible with crystal growth monitoring by optical microscopy. The quality of the protein 3D structures derived from on-chip crystal analysis by X-ray diffraction using a synchrotron radiation was used to identify the most appropriate polymers. Altogether the results demonstrate that for a novel biomolecule, all steps from the initial search of crystallization conditions to X-ray diffraction data collection for 3D structure determination can be performed in a single chip.
Lab on a Chip 06/2009; 9(10):1412-21. · 5.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An acrylate monolith has been synthesized into a cyclic olefin copolymer microdevice for reversed-phase electrochromatography purposes. Microchannels, designed by hot embossing, were filled up with an acrylate monolith to serve as a hydrophobic stationary phase. A lauryl acrylate monolith was formulated to suit the hydrophobic material, by implementing 100% organic porogenic solvent. This new composition was tested in capillary prior to its transfer into the microfluidic device. Surface functionalization of the cyclic olefin copolymer surface was applied using UV-grafting technique to improve the covalent attachment of this monolith to the plastic walls of the microfluidic chip. The on-chip performances of this monolith were evaluated in detail for the reversed-phase electrochromatographic separation of polycyclic aromatic hydrocarbons, with plate heights reaching down to 10 microm when working at optimal velocity.
[Show abstract][Hide abstract] ABSTRACT: A microfluidic glucose/O2 biofuel cell, delivering electrical power, is developed based on both laminar flow and biological enzyme strategies. The device consists of a Y-shaped microfluidic channel in which fuel and oxidant streams flow laminarly in parallel at gold electrode surfaces without convective mixing. At the anode, the glucose is oxidized by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in the presence of specific redox mediators. Such cell design protects the anode from interfering parasite reaction of O2 at the anode and works with different streams of oxidant and fuel for optimal operation of the enzymes. The dependence of the flow rate on the current is evaluated in order to determine the optimum flow that would provide little to no mixing while yielding high current densities. The maximum power density delivered by the assembled biofuel cell reaches 110 μW cm−2 at 0.3 V with 10 mM glucose at 23 °C. This research demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O2 biofuel cell device.
[Show abstract][Hide abstract] ABSTRACT: A Y-shaped microfluidic channel is applied for the first time to the construction of a glucose/O2 biofuel cell, based on both laminar flow and biological enzyme strategies. During operation, the fuel and oxidant streams flow parallel at gold electrode surfaces without convective mixing. At the anode, the glucose oxidation is performed by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in the presence of specific redox mediators. Such cell design protects the anode from an interfering parasite reaction of O2 at the anode and offers the advantage of using different streams of oxidant and fuel for optimal performance of the enzymes. Electrochemical characterizations of the device show the influence of the flow rate on the output potential and current density. The maximum power density delivered by the assembled biofuel cell reached 110 μW cm−2 at 0.3 V with 10 mM glucose at 23 °C. The microfluidic approach reported here demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O2 biofuel cell device.
[Show abstract][Hide abstract] ABSTRACT: This paper describes a microfluidic device fabricated in poly(dimethylsiloxane) that was employed to perform amperometric quantifications using on-chip calibration curves and on-chip standard addition methods. This device integrated a network of Au electrodes within a microfluidic structure designed for automatic preparation of a series of solutions containing an electroactive molecule at a concentration linearly decreasing. This device was first characterized by fluorescence microscopy and then evaluated with a model electroactive molecule such as Fe(CN(6))(4-). Operating a quantification in this microfluidic parallel approach rather than in batch mode allows a reduced analysis time to be achieved. Moreover, the microfluidic approach is compatible with the on-chip calibration of sensors simultaneously to the analysis, therefore preventing problems due to sensor response deviation with time. When using the on-chip calibration and on-chip standard addition method, we reached concentration estimation better than 5%. We also demonstrated that compared to the calibration curve approach, the standard addition mode is less complex to operate. Indeed, in this case, it is not necessary to take into account flow rate discrepancies as in the calibration approach.
The Analyst 01/2009; 134(3):472-477. · 3.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper describes two configurations that integrate electrochemical detection into microfluidic devices. The first configuration is a low-cost approach based on the use of PCB technology. This device was applied to electrochemiluminescence detection. The second configuration was used to carry out amperometric quantification of electroactive species using a serial dilution microfluidic system.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2009; 2009:4144-6.
[Show abstract][Hide abstract] ABSTRACT: This paper presents the design of two configurations of electrodes ("gold versus Ag/AgCl" and "gold versus gold") and an electrochemiluminescence (ECL) microfluidic device fabricated in the inexpensive printed circuit board (PCB) technology. The PCB electrodes are electrochemically characterized to determine appropriate working potentials. The ECL microfluidic device with integrated PCB electrodes is tested using luminol as luminophore to quantify H<sub>2</sub>O<sub>2</sub> concentrations. Synchronous detection technique is implemented for weak signal recovery. For both PCB electrode configurations, a 100 nM H<sub>2</sub>O<sub>2</sub> concentration is detected and a linear range extending from 100 nM to 10 mM is observed with a photomultiplier tube. A lab-on-board compatible potentiostat and a compact CMOS photodetector module are also designed and validated. The proposed instrumental approach may represent a low-cost way to develop portable analytical systems.
[Show abstract][Hide abstract] ABSTRACT: In this work, we developed a PDMS electrophoresis device able to carry out on-chip derivatization and quantification of amino acids (AAs) using naphthalene-2,3-dicarboxaldehyde (NDA) as a fluorogenic agent. A chemical modification of the PDMS surface was found compulsory to achieve the derivatization of AAs with NDA and a limit of detection (LOD) of 40nM was reached for glycine. Finally, we suggested the applicability of this microdevice for the analysis of real biological samples such as a rat hippocampus microdialysate.