Editing Digital microfluidics (section)

=== From an existing droplet ===
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,<ref name="Fair_2007" /> this droplet will move towards both active electrodes. Liquid moves to either side, which causes the middle of the droplet to neck.<ref name="Cho_2003" /> For a droplet of the same size as the electrodes, splitting will occur approximately when <math>R_{neck}/R_{end}=-1</math>, as the neck will be at its thinnest.<ref name="Cho_2003" /> <math>R_{neck}</math> is the [[radius of curvature]] of the [[Meniscus (liquid)|menisci]] at the neck, which is negative for a concave curve, and <math>R_{end}</math> 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.<ref name="Cho_2003" /><ref name="Teh_2008">{{cite journal | vauthors = Teh SY, Lin R, Hung LH, Lee AP | title = Droplet microfluidics | journal = Lab on a Chip | volume = 8 | issue = 2 | pages = 198–220 | date = February 2008 | pmid = 18231657 | doi = 10.1039/B715524G }}</ref>

The conventional method<ref name="Pollack_2000">{{Cite journal| vauthors = Pollack MG, Fair RB, Shenderov AD|date=2000-09-11|title=Electrowetting-based actuation of liquid droplets for microfluidic applications|journal=Applied Physics Letters|volume=77|issue=11|pages=1725–1726|doi=10.1063/1.1308534|bibcode=2000ApPhL..77.1725P|issn=0003-6951}}</ref><ref name="Cho_2003" /> of splitting an existing droplet by simply turning the splitting electrodes on and off produces new droplets of relatively equal volume. However, the new droplets formed by the conventional method show considerable difference in volume.<ref>{{Cite journal| vauthors = Nikapitiya NY, Nahar MM, Moon H |date=2017-06-16|title=Accurate, consistent, and fast droplet splitting and dispensing in electrowetting on dielectric digital microfluidics|journal=Micro and Nano Systems Letters|volume=5|issue=1|page=24|doi=10.1186/s40486-017-0058-6|bibcode=2017MNSL....5...24N|issn=2213-9621|doi-access=free}}</ref><ref name="Banerjee_2012">{{cite journal | vauthors = Banerjee A, Liu Y, Heikenfeld J, Papautsky I | title = Deterministic splitting of fluid volumes in electrowetting microfluidics | journal = Lab on a Chip | volume = 12 | issue = 24 | pages = 5138–5141 | date = December 2012 | pmid = 23042521 | doi = 10.1039/c2lc40723j }}</ref> This difference is caused by local perturbations due to the rapid mass transport.<ref name="Banerjee_2012" /> Even though the difference is negligible in some applications, it can still pose a problem in applications that are highly sensitive to variations in volume,<ref name="Liu_2014">{{Cite journal| vauthors = Liu Y, Banerjee A, Papautsky I |date=2014-01-10|title=Precise droplet volume measurement and electrode-based volume metering in digital microfluidics|journal=Microfluidics and Nanofluidics|volume=17|issue=2|pages=295–303|doi=10.1007/s10404-013-1318-2|s2cid=16884950|issn=1613-4982}}</ref><ref>{{Cite journal| vauthors = Vergauwe N, Witters D, Atalay YT, Verbruggen B, Vermeir S, Ceyssens F, Puers R, Lammertyn J | display-authors = 6 |date=2011-01-26|title=Controlling droplet size variability of a digital lab-on-a-chip for improved bio-assay performance|journal=Microfluidics and Nanofluidics|volume=11|issue=1|pages=25–34|doi=10.1007/s10404-011-0769-6|s2cid=93039641|issn=1613-4982}}</ref> such as immunoassays<ref>{{cite journal | vauthors = Shamsi MH, Choi K, Ng AH, Wheeler AR | title = A digital microfluidic electrochemical immunoassay | journal = Lab on a Chip | volume = 14 | issue = 3 | pages = 547–554 | date = February 2014 | pmid = 24292705 | doi = 10.1039/c3lc51063h }}</ref> and DNA amplification.<ref>{{cite journal | vauthors = Chang YH, Lee GB, Huang FC, Chen YY, Lin JL | title = Integrated polymerase chain reaction chips utilizing digital microfluidics | journal = Biomedical Microdevices | volume = 8 | issue = 3 | pages = 215–225 | date = September 2006 | pmid = 16718406 | doi = 10.1007/s10544-006-8171-y | s2cid = 21275449 }}</ref> To overcome the limitation of the conventional method, an existing droplet can be split by gradually changing the potential of the electrodes at the splitting region instead of simply switching them on and off.<ref name="Banerjee_2012" /> Using this method, a noticeable improvement in droplet volume variation, from around 10% variation in volume to less than 1% variation in volume, has been reported.<ref name="Banerjee_2012" />