Digital microfluidic has recently been under intensive study, as an effective method to carry out liquid manipulation in Lab-On-a-Chip (LOC) systems. Among droplet actuation forces, ElectroWetting on Dielectric (EWOD) and Liquid DiElectroPhoresis (LDEP) are powerful tools, used in many LOC platforms. Such digital microfluidic transductions do not require integration of complex mechanical components such as pumps and valves to perform the fluidic operations. However, although LDEP has been proved to be efficient to carry and manipulate biological components in insulating liquids, this microfluidic transduction requires several hundreds of volts at relatively high frequencies (kHz to MHz). With the purpose to develop integrated microsystems µ-TAS (Micro Total Analysis System) or Point of Care systems, the goal here is to reduce such high actuation voltage, the power consumption, though using standard dielectric materials. This paper gives key rules to determine the best tradeoff between liquid manipulation efficiency, low-power consumption and robustness of microsystems using LDEP actuation. This study leans on an electromechanical model to describe liquid manipulation that is applied to an experimental setup, and provides precise quantification of both actuation voltage V_th and frequency f_c thresholds between EWOD and LDEP regimes. In particular, several parameters will be investigated to quantify V_th and f_c, such as the influence of the chip materials, the electrodes size and the device configurations. Compared to current studies in the field, significant reduction of both V_th and f_c is achieved by optimization of the aforementioned parameters.

This article reports an original concept enabling the rapid fabrication of continuous-flow microfluidic chips with a programmable and reconfigurable geometry. The concept is based on a digital microfluidic platform featuring an array of individually addressable electrodes. A selection of electrodes is switched on sequentially to create a de-ionized (DI) water finger specific pattern, while the surrounding medium consists of liquid-phase paraffin. The water displacement is induced by both electrowetting on dielectric and liquid dielectrophoresis phenomena. Once the targeted DI water pattern is obtained, the chip temperature is lowered by turning on an integrated thermoelectric cooler, forming channel structures made of solidified paraffin with edges delimitated by the DI water pattern. As a result, the chip can be used afterwards to conduct in-flow continuous microfluidic experiments. This process is resettable and reversible by heating up the chip to melt the paraffin and reconfigure the microchannel design on demand, offering the advantages of cost, adaptability, and robustness. This paper reports experimental results describing the overall concept, which is illustrated with typical and basic fluidic geometries.

The generation of droplets for biological reactions at the microscale can be achieved by many techniques, among which the so-called liquid dielectrophoresis technique (LDEP). This is not a new process, but the parameters influencing actuation voltage still need further insight: size and geometry (electrodes width and gap, dielectric thickness), materials (dielectric constant), liquids (surface tension, dielectric constant, conductivity), working conditions (voltage, frequency) and substrate wettability (contact angle). This large experimental space is firstly reduced using non dimensional numbers and then studied in a systematic way thanks to the design of experiments. The contact angle influence is explained thanks to a new analytical model. To summarize, this paper recalls analytical models used to predict the voltage threshold required to develop a liquid rivulet from a mother drop, taking the contact angle into account and providing a large set of experimental results.

This study presents a new application of Liquid DiElectroPhoresis (LDEP) for local surface functionalization of a planar substrate. Circular spots (diameter ranging from 24 to 100 μm) made of PolyEthyleneImine (PEI) polymer can be accurately positioned, after evaporation of sessile microdroplets, created by LDEP, from a solute polymer. This local surface modification is validated by trapping of Bacillus subtilis spores onto these spots.