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A conducting droplet set on the lower plate of a condenser acquires an electrical charge when subjected to an electrical field. Above a threshold value the electrical force lifts the droplet. If the droplet's charge does not leak away, the droplet moves up to the upper electrode and bounces on it. Coating the upper electrode with a dielectric layer allows the otherwise regular droplet back and forth motion to be controlled. This new idea is applied to a droplet-based microfluidic system which drives droplets by electrowetting on a planar array. In this way additional flexibility is achieved since droplets can be displaced and controlled in the three space dimensions.

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The detection of airborne pathogens is becoming a subject of great concern in modern day society. Recent studies have shown that electrostatic samplers are suitable for collecting microorganisms as well as preserving their viability. In most of these studies, flow rates were lower than 12.5 L/min or required a concentration stage to increase the flow rate to 100 L/min. In the present study, a single stage electrostatic sampler was developed for an efficient collection of microorganisms at 100 L/min. The design is based on the positive DC corona between coaxial cylinders to continuously create charged particles as they pass through the sampler. The physical collection efficiency of the device was investigated by sampling the ambient air particles. The efficiency in collecting live biological samples was determined by sampling live bacterial spores with the collector situated inside an aerosol chamber. It is shown that particles of 0.3-0.35 µm are captured with an efficiency of about 86%, whereas cultivable spores of Bacillus thuringiensis are collected with an efficiency of about 94%. Results are compared with an analytical predictive model. The experimental results are similar to the efficiencies previously reported in the literature; however, the current sampler design features a higher flow rate which enables the device to be used as an alarm trigger in a shorter period of time.

Airborne particles are known to cause illness and to influence meteorological phenomena. It is therefore important to monitor their concentrations and to identify them. A challenge is to collect micro and nanoparticles, microorganisms as well as toxic molecules with a device as simple and small as possible to be used easily and everywhere. Electrostatic precipitation is an efficient method to collect all kinds of airborne particles. Furthermore, this method can be miniaturized. A portable, silent, and autonomous air sampler based on this technology is therefore being developed with the final objective to collect very efficiently airborne pathogens such as supermicron bacteria but also submicron viruses. Particles are collected on a dry surface so they may be concentrated afterwards in a small amount of liquid medium to be analyzed. It is shown that nearly 98 % of airborne particles from 10 nm to 3 μm are collected.

This paper presents a brief overview of Electro Wetting On Dielectric (EWOD) microdroplet actuation technology fluidic behaviour. EWOD specifics are compared with other digital microfluidics actuation modes. In particular ease of integration with complex protocols is emphasized. After reviewing the electro-wetting principle and various Electro-Hydro-Dynamic (EHD) phenomena; we compare various EWOD configurations for Lab on a Chip. Two fluid functionalities will be detailed: on-chip droplet dispensing, and mixing. We cover chip architecture and the benefits of organizing these chips as fludic microprocessors. Finally, real time PCR (Polymerase Chain Reaction) within a 64 nl droplet is described as an illustration of a biological application using EWOD.

A single conducting drop resting on the lower plane electrode of a horizontal condenser and surrounded by a dielectric fluid is considered. When a DC field is applied to the electrodes, the drop acquires electric charges and is subjected to an electrostatic force normal to the electrode. This driving force may eventually detach the drop if the applied field strength exceeds a threshold value. For small drops, the gravitational field and the electrical force effect can be neglected with respect to the surface tension. In this case, it may be assumed that drops are undeformable and keep a spherical cap shape. Based on this model, charges and forces are calculated analytically in any wetting conditions. To this end, previous studies concerning solid spheres are conveniently extended. The usefulness of the above model is then considered to determine the lift-off threshold value. For non-wetting conditions, new experimental results are presented: they fit precisely the derived theoretical lift-off conditions. For wetting conditions, the preceding calculations are shown to be unable to provide any testable criterion. The undeformability assumption has to be relaxed.