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ABSTRACT: Droplet based microfluidic systems, in recent years, have demonstrated numerous advantages and exciting potential for Lab-On-a Chip applications. In order to fully realize the potential benefits of this technology, one requires precision dispensing and manipulation of droplets of known volume and sample concentration, in a rapid and controlled manner. In this article, we demonstrate the rapid and controlled microactuation of aqueous samples and subsequent dispensing of variable volume droplets in nanolitre to picolitre regime by using a coplanar tapered electrode structure that leverages the phenomena of liquid dielectrophoresis (L-DEP). The transient behavior of the tapered liquid jet departs significantly from that of a uniform liquid jet case and is not adequately explained in terms of a simplified lumped capacitance model as in the case of the uniform jet, during the L-DEP actuation. A more generalized numerical model is developed for the tapered actuation scheme to account for the experimental observations. We furthermore demonstrate that the density of the dispensed droplets can be proactively controlled by the judicious placement of electrode bumps and pinches in the electrode structure thus overcoming the limitations imposed by Rayleigh's instability criterion. The proposed droplet dispensing schemes are superior to existing L-DEP based dispensing schemes which are restricted in size and spacing of the dispensed droplets by Rayleigh's instability criteria and furthermore mostly restricted to equi-volume droplets.
Lab on a Chip 11/2010; 10(22):3094-102. · 5.67 Impact Factor
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BIODEVICES 2010 - Proceedings of the Third International Conference on Biomedical Electronics and Devices, Valencia, Spain, January 20-23, 2010; 01/2010
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ABSTRACT: Liquid dielectrophoresis (L-DEP), when deployed at microscopic scales on top of hydrophobic surfaces, offers novel ways of rapid and automated manipulation of very small amounts of polar aqueous samples for microfluidic applications and development of laboratory-on-a-chip devices. In this article we highlight some of the more recent developments and applications of L-DEP in handling and processing of various types of aqueous samples and reagents of biological relevance including emulsions using such microchip based surface microfluidic (SMF) devices. We highlighted the utility of these devices for on-chip bioassays including nucleic acid analysis. Furthermore, the parallel sample processing capabilities of these SMF devices together with suitable on- or off-chip detection capabilities suggest numerous applications and utility in conducting automated multiplexed assays, a capability much sought after in the high throughput diagnostic and screening assays.
Biomicrofluidics 01/2010; 4(2). · 3.37 Impact Factor
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ABSTRACT: Liquid Dielectrophoresis (L-DEP) has been successfully leveraged at microscopic scales and shown to provide a controllable means of on-chip precision dispensing and manipulation of sub-nanoliter single emulsion droplets. In this paper, we report on the dynamics of a DEP actuated emulsion jet prior to break-up and compare its characteristic behavior based on the lumped parameter model of Jones et al. (R. Ahmed and T. B. Jones, J. Micromech. Microeng., 2007, 17, 1052). Furthermore, features and aspects of these emulsion jets, their break-up and formation of sub-nanoliter emulsion droplets is studied in further detail. Applications of the proposed scheme in dispensing encapsulated sub-nanoliter droplets is envisioned in various fields including microTAS, on-chip handling and storage of cells and other biological samples for longer duration in controlled environments as well as solving the more general encapsulation issues in surface microfluidic devices. Scalability of the proposed scheme is shown by producing controlled sample-oil single emulsion droplets (aqueous samples in oil) in the range of 50-400 picoliters.
Lab on a Chip 10/2009; 9(19):2836-44. · 5.67 Impact Factor
