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Micromachines 2017, 8(12), 353;

Electrical Tweezer for Droplet Transportation, Extraction, Merging and DNA Analysis

Department of Mechanical Engineering, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4L7, Canada
Regional Virology Laboratory, St. Joseph’s Healthcare Hamilton, Hamilton, ON L8N 4A6, Canada
Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON L8S 4L8 Canada
Department of Electrical and Computer Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada
Author to whom correspondence should be addressed.
Received: 1 November 2017 / Revised: 21 November 2017 / Accepted: 28 November 2017 / Published: 30 November 2017
(This article belongs to the Special Issue Biomedical Microdevices: Design, Fabrication and Application)
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Droplets of aqueous solutions distributed in an immiscible oil phase are increasingly used and investigated as a means to handle and assay small volumes of samples. The primary attraction of this method is that surface interactions are kept to a minimum, and changes in sample concentration, especially due to adsorption to the walls, are avoided. Microfluidic methods to generate, transport, merge, split and perform reactions in droplets were developed recently. These methods depend on the continuous flow of the two phases involved inside closed microfluidic channels. Alternatively, an electrowetting phenomenon was also exploited to control the movement of droplets between two solid substrates. However, there are some situations where small volume sample transport and assaying are required in open systems. Here, we demonstrate a simple electromechanical probe (tweezers) that is capable of manipulating a small aqueous droplet in a bi-layer oil phase. The tweezer consists of two needles positioned close to each other and uses polarization of the aqueous droplet in an applied electrical field to confine the droplet between the needles with minimal solid contact. Mechanical motion of the tweezer can be used to transport the droplet to various positions. Operations such as aliquoting, merging and transport are demonstrated. Finally, this method was used to perform a DNA amplification assay where droplets of the sample and the amplification mixture are aliquoted separately, mixed and amplified using an in-situ heater. This electromechanical tweezer is of interest in low-throughput, small-volume biological and chemical assays where the investigator requires direct and open access to the samples. View Full-Text
Keywords: droplets; electrical tweezer; microfluidics; amplification; nanoliter; droplet extraction; droplet merging; droplet transportation droplets; electrical tweezer; microfluidics; amplification; nanoliter; droplet extraction; droplet merging; droplet transportation

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Shahid, A.; Chong, S.; Mahony, J.; Deen, M.J.; Selvaganapathy, P.R. Electrical Tweezer for Droplet Transportation, Extraction, Merging and DNA Analysis. Micromachines 2017, 8, 353.

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