Magnetically controlled dielectrophoresis of metallic colloids

Peer reviewed: YesNRC publication: Ye

Improving the reliability and complexity of advanced electrowetting-based digital microfluidic devices

Peer reviewed: YesNRC publication: Ye

Modélisation des processus d'aimantation des réseaux de nanofils ferromagnétiques amorphes

Méthodes de modélisation micromagnétique -- Études des nanofils et des réseaux de nanofils -- Modélisation des champs et des processus d'animation

Numerical modeling of electrowetting processes in digital microfluidic devices

We use a three-dimensional multiphase lattice-Boltzmann model to study basic operations such as transport, merging and splitting of nanoliter water droplets actuated by electrowetting in digital microfluidic devices. In a first step, numerical and analytical predictions for the droplet transport velocity are compared and very good agreement is obtained for a wide range of contact angles. The same algorithm is employed then to study the dynamics of the splitting processes at different contact angles and different geometries of the cell. The configuration of the liquid droplet involved in a splitting process and the dependence of the splitting time on the transport velocity are also investigated and phenomenological laws describing these processes are also proposed.Nous avons utilis\ue9 un mod\ue8le 3D \ue0 plusieurs phases de type lattice-Boltzmann pour \ue9tudier des ph\ue9nom\ue8nes de base tels que le transport, la fusion et le fractionnement de gouttelettes d'eau de l\u2019ordre du nanolitre actionn\ue9 par \ue9lectromouillage \ue0 l\u2019aide de dispositifs microfluidiques num\ue9riques. Nous avons, dans un premier temps, compar\ue9 les pr\ue9dictions num\ue9riques et analytiques concernant la vitesse de transport des gouttes et obtenu des r\ue9sultats coh\ue9rents pour une gamme \ue9tendue d'angles de contact. Nous avons ensuite utilis\ue9 le m\ueame algorithme pour \ue9tudier la dynamique des processus de fractionnement selon des angles de contact et des g\ue9om\ue9tries cellulaires diff\ue9rentes. Nous avons \ue9galement analys\ue9 la configuration de la gouttelette liquide durant le processus de fractionnement ainsi que la d\ue9pendance du temps de fractionnement vis-\ue0-vis de la vitesse de transport. Nous proposons ici des lois ph\ue9nom\ue9nologiques qui d\ue9crivent ces processus.Peer reviewed: YesNRC publication: Ye

Numerical modeling of electrowetting processes in digital microfluidic devices

We use a three-dimensional multiphase lattice-Boltzmann model to study basic operations such as transport, merging and splitting of nanoliter water droplets actuated by electrowetting in digital microfluidic devices. In a first step, numerical and analytical predictions for the droplet transport velocity are compared and very good agreement is obtained for a wide range of contact angles. The same algorithm is employed then to study the dynamics of the splitting processes at different contact angles and different geometries of the cell. The configuration of the liquid droplet involved in a splitting process and the dependence of the splitting time on the transport velocity are also investigated and phenomenological laws describing these processes are also proposed.Nous avons utilis\ue9 un mod\ue8le 3D \ue0 plusieurs phases de type lattice-Boltzmann pour \ue9tudier des ph\ue9nom\ue8nes de base tels que le transport, la fusion et le fractionnement de gouttelettes d'eau de l\u2019ordre du nanolitre actionn\ue9 par \ue9lectromouillage \ue0 l\u2019aide de dispositifs microfluidiques num\ue9riques. Nous avons, dans un premier temps, compar\ue9 les pr\ue9dictions num\ue9riques et analytiques concernant la vitesse de transport des gouttes et obtenu des r\ue9sultats coh\ue9rents pour une gamme \ue9tendue d'angles de contact. Nous avons ensuite utilis\ue9 le m\ueame algorithme pour \ue9tudier la dynamique des processus de fractionnement selon des angles de contact et des g\ue9om\ue9tries cellulaires diff\ue9rentes. Nous avons \ue9galement analys\ue9 la configuration de la gouttelette liquide durant le processus de fractionnement ainsi que la d\ue9pendance du temps de fractionnement vis-\ue0-vis de la vitesse de transport. Nous proposons ici des lois ph\ue9nom\ue9nologiques qui d\ue9crivent ces processus.Peer reviewed: YesNRC publication: Ye

The influence of magnetic carrier size on the performance of microfluidic integrated micro-electromagnetic traps

Efficient manipulation and capture of magnetic carriers in fluid stream require appropriate magnetic confinement devices whose performances are strongly dependent on the nature of the magnetic carriers. In this sense, we have performed a systematic investigation of the magnetic capture efficiencies for five commercially available superparamagnetic particles pumped along rectangular microfluidic channels using microelectromagnetic traps composed of planar circular current-carrying microwires and cylindrical ferromagnetic posts. In addition, in order to obtain a quantitative description of particle movement, we have implemented a numerical model for the dynamics of magnetic objects subjected to magnetic field gradients in conventional continuous-flow microfluidic devices. Fully 3D trajectories of the particles, effective cross-sectional areas of the microchannel as well as micro-electromagnet trapping efficiencies are compared to experimental measurements and a very good agreement is obtained. Finally, a simple and effective analytical model to determine the critical velocity, i.e. when the magnetic trapping device is no longer able to capture and hold 100% of the magnetic superparamagnetic particles, is also presented.Peer reviewed: YesNRC publication: Ye

Active pneumatic control of centrifugal microfluidic flows for lab-on-a-chip applications

This paper reports a novel method of controlling liquid motion on a centrifugal microfluidic platform based on the integration of a regulated pressure pump and a programmable electromechanical valving system. We demonstrate accurate control over the displacement of liquids within the system by pressurizing simultaneously multiple ports of the microfluidic device while the platform is rotating at high speed. Compared to classical centrifugal microfluidic platforms where liquids are solely driven by centrifugal and capillary forces, the method presented herein adds a new degree of freedom for fluidic manipulation, which represents a paradigm change in centrifugal microfluidics. We first demonstrate how various core microfluidic functions such as valving, switching, and reverse pumping (i.e., against the centrifugal field) can be easily achieved by programming the pressures applied at dedicated access ports of the microfluidic device. We then show, for the first time, that the combination of centrifugal force and active pneumatic pumping offers the possibility of mixing fluids rapidly (~0.1 s) and efficiently based on the creation of air bubbles at the bottom of a microfluidic reservoir. Finally, the suitability of the developed platform for performing complex bioanalytical assays in an automated fashion is demonstrated in a DNA harvesting experiment where recovery rates of about 70% were systematically achieved. The proposed concept offers the interesting prospect to decouple basic microfluidic functions from specific material properties, channel dimensions and fabrication tolerances, surface treatments, or on-chip active components, thus promoting integration of complex assays on simple and low-cost microfluidic cartridges.Peer reviewed: YesNRC publication: Ye

Dynamics of superparamagnetic and ferromagnetic nano-objects in continuous-flow microfluidic devices

We present a numerical study on the dynamics of magnetic micro- and nano-objects subjected to magnetic field gradients in conventional continuous-flow microfluidic devices. By a mixed finite-element/discrete-element approach we solve the equations of the field driven motion for magnetic nano-objects floating in liquids at very low Reynolds numbers and compare the magnetic trapping efficiency of commercially available superparamagnetic microbeads to that of ferromagnetic nanowires. The drag force and the remanent magnetization of ferromagnetic nanowires are found to be responsible for the huge increase of their magnetic trappability whereas the slip-length associated with the Navier boundary condition at the transition to the nanoscale regime is found to be a much less important parameter.Peer reviewed: YesNRC publication: Ye