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Droplet Formation edit
There are two ways to make new droplets with a digital microfluidic device. Either an existing droplet can be split apart, or a new droplet can be made from a reservoir of material.[1] Both processes can generally only be done in a closed device,[2][3] though this often is not a problem as the top plates of DMF devices are typically removable,[4] so an open device can be made temporarily closed should droplet formation be necessary.
From a an Existing Droplet edit
A droplet can be split by charging two electrodes on opposite sides of a droplet on an uncharged electrode. In the same way a droplet on an uncharged electrode will move towards an adjacent, charged electrode,[5] this droplet will move towards both active electrodes. Liquid moves to either side, which causes the middle of the droplet to neck[1] For a droplet of the same size as the electrodes, splitting will occur approximately when , as the neck will be at its thinnest.[1] is the radius of curvature of the menisci at the neck, which is negative for a concave curve, and is the radius of curvature of the menisci at the elongated ends of the droplet. This process is simple and consistently results in two droplets of equal volume.[1][6]
From a Reservoir edit
Creating a new droplet from a reservoir of liquid can be done in a similar fashion to splitting a droplet. In this case, the reservoir remains stationary while a sequence of electrodes are used to draw liquid out of the reservoir. This drawn liquid and the reservoir form a neck of liquid, akin to the neck of a splitting droplet but longer, and the collapsing of this neck forms a dispensed droplet from the drawn liquid.[1][7] In contrast to splitting, though, dispensing droplets in this manner is inconsistent in scale and results. There is no reliable distance liquid will need to be pulled from the reservoir for the neck to collapse, if it even collapses at all.[8] Because this distance varies, the volumes of dispensed droplets will also vary within the same device.[8][9] Due to these inconsistencies, alternative techniques for dispensing droplets have been proposed, including drawing liquid out of reservoirs in geometries that force a thinner neck[1][10] and moving reservoirs into corners so as to cut the reservoir down the middle.[6][10] Multiple iterations of the latter can produce droplets of more manageable sizes.[6][10]
- ^ a b c d e f Sung Kwon Cho; Hyejin Moon; Chang-Jin Kim (2003). "Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits". Journal of Microelectromechanical Systems. 12 (1): 70–80. doi:10.1109/JMEMS.2002.807467. ISSN 1057-7157.
- ^ Berthier, Jean (2013). Micro-Drops and Digital Microfluidics. William Andrew. pp. 261–263. ISBN 9781455728008.
- ^ Chang, Jong-Hyeon; Kim, Dong-Sik; Pak, James Jung-Ho (2011-05-02). "Simplified Ground-type Single-plate Electrowetting Device for Droplet Transport". Journal of Electrical Engineering and Technology. 6 (3): 402–407. doi:10.5370/JEET.2011.6.3.402. ISSN 1975-0102.
- ^ Kirby, Andrea E.; Wheeler, Aaron R. (2013-07-02). "Digital Microfluidics: An Emerging Sample Preparation Platform for Mass Spectrometry". Analytical Chemistry. 85 (13): 6178–6184. doi:10.1021/ac401150q. ISSN 0003-2700.
- ^ Fair, Richard B.; Khlystov, Andrey; Tailor, Tina D.; Ivanov, Vladislav; Evans, All D.; Srinivasan, Vijay; Pamula, Vamsee K.; Pollack, Michael G.; Griffin, Peter B. (2006). "Chemical and biological applications of digital microfluidic devices". IEEE Des. Test Comput: 10–24.
- ^ a b c Lee, Abraham P.; Hung, Lung-Hsin; Lin, Robert; Teh, Shia-Yen (2008-01-29). "Droplet microfluidics". Lab on a Chip. 8 (2): 198–220. doi:10.1039/B715524G. ISSN 1473-0189.
- ^ Shih-Kang Fan; Hashi, C.; Chang-Jin Kim (2003). "Manipulation of multiple droplets on N/spl times/M grid by cross-reference EWOD driving scheme and pressure-contact packaging". IEEE The Sixteenth Annual International Conference on Micro Electro Mechanical Systems, 2003. MEMS-03 Kyoto: 694–697. doi:10.1109/MEMSYS.2003.1189844.
- ^ a b Elvira, Katherine S.; Leatherbarrow, Robin; Edel, Joshua; deMello, Andrew (2012-04-06). "Droplet dispensing in digital microfluidic devices: Assessment of long-term reproducibility". Biomicrofluidics. 6 (2): 022003–022003–10. doi:10.1063/1.3693592. ISSN 1932-1058. PMC 3360711. PMID 22655007.
{{cite journal}}: CS1 maint: PMC format (link) - ^ Wijethunga, Pavithra A. L.; Nanayakkara, Yasith S.; Kunchala, Praveen; Armstrong, Daniel W.; Moon, Hyejin (2011). "On-Chip Drop-to-Drop Liquid Microextraction Coupled with Real-Time Concentration Monitoring Technique". Analytical Chemistry. 83 (5): 1658–1664. doi:10.1021/ac102716s. ISSN 0003-2700.
- ^ a b c Nikapitiya, N. Y. J. B.; You, S. M.; Moon, H. (2014). "Droplet dispensing and splitting by electrowetting on dielectric digital microfluidics". 2014 IEEE 27th International Conference on Micro Electro Mechanical Systems (MEMS): 955–958. doi:10.1109/MEMSYS.2014.6765801.