Editing Digital microfluidics (section)

=== Displacement by electrostatic actuation ===
Three-dimensional droplet actuation has been made possible by implementing a closed system; this system contains a μL sized droplet in immiscible fluid medium. The droplet and medium are then sandwiched between two electromagnetic plates, creating an EM field between the two plates.<ref name="Roux_2007">{{cite journal | vauthors = Roux JM, Fouillet Y, Achard JL | title = 3D droplet displacement in microfluidic systems by electrostatic actuation. | journal = Sensors and Actuators A: Physical | date = March 2007 | volume = 134 | issue = 2 | pages = 486–93 | doi = 10.1016/j.sna.2006.05.012 | bibcode = 2007SeAcA.134..486R | s2cid = 108644890 | url = https://hal.archives-ouvertes.fr/hal-00267651/file/Roux2007.pdf }}</ref><ref>{{cite journal | vauthors = Fouillet Y, Achard JL | title = Microfluidique discrète et biotechnologie. | journal = Comptes Rendus Physique | date = June 2004 | volume = 5 | issue = 5 | pages = 577–88 | doi = 10.1016/j.crhy.2004.04.004 | bibcode = 2004CRPhy...5..577F | url = https://hal.archives-ouvertes.fr/hal-00182327/file/fouillet2004.pdf }}</ref> The purpose of this method is to transfer the droplet from a lower planar surface to an upper parallel planar surface and back down via electrostatic forces.<ref name="Roux_2007" /><ref name="Kolar_2001">{{cite conference | vauthors = Kolar P, Fair RB | title = Non-contact electrostatic stamping for DNA microarray synthesis (poster) | conference = Proceedings of the SmallTalk2001 | location = San Diego, USA | date = 2001 }}</ref> The physics behind such particle actuation and perpendicular movement can be understood from early works of N. N. Lebedev and I. P. Skal’skaya.<ref name="Lebedev_1962">{{cite journal | vauthors = Lebedev NN, Skal'skaya IP | title = Force acting on a conducting sphere in the field of a parallel plate condenser | journal = Soviet Phys. Tech. Phys. | volume = 7 | date = 1962 | pages = 268–270 }}</ref> In their research, they attempted to model the Maxwell electrical charge acquired by a perfectly round conducting particle in the presence of a uniform magnetic field caused by a perfectly-conducting and infinitely-stretching surface.<ref name="Lebedev_1962" /> Their model helps to predict the Z-direction motion of the microdroplets within the device as it points to the magnitude and direction of forces acting upon a micro droplet. This can be used to help accurately predict and correct for unwanted and uncontrollable particle movement. The model explains why failing to employ dielectric coating on one of the two surfaces causes reversal of charge within the droplet upon contact with each electrode and in turn causes the droplets to uncontrollably bounce of between electrodes.

Digital microfluidics (DMF), has already been readily adapted in many biological fields.<ref>{{cite journal | vauthors = Velev OD, Prevo BG, Bhatt KH | title = On-chip manipulation of free droplets | journal = Nature | volume = 426 | issue = 6966 | pages = 515–6 | date = December 2003 | pmid = 14654830 | doi = 10.1038/426515a | bibcode = 2003Natur.426..515V | s2cid = 21293602 }}</ref><ref name="Gascoyne_2004">{{cite journal | vauthors = Gascoyne PR, Vykoukal JV, Schwartz JA, Anderson TJ, Vykoukal DM, Current KW, McConaghy C, Becker FF, Andrews C | title = Dielectrophoresis-based programmable fluidic processors | journal = Lab on a Chip | volume = 4 | issue = 4 | pages = 299–309 | date = August 2004 | pmid = 15269795 | doi = 10.1039/b404130e }}</ref><ref name="Taniguchi_2002">{{cite journal | vauthors = Taniguchi T, Torii T, Higuchi T | title = Chemical reactions in microdroplets by electrostatic manipulation of droplets in liquid media | journal = Lab on a Chip | volume = 2 | issue = 1 | pages = 19–23 | date = February 2002 | pmid = 15100855 | doi = 10.1039/b108739h }}</ref> By enabling three-dimensional movement within DMF, the technology can be used even more extensively in biological applications, as it could more accurately mimic 3-D microenvironments. A large benefit of employing this type of method is that it allows for two different environments to be accessible by the droplet, which can be taken advantage of by splitting the microfluidic tasks among the two surfaces. For example, while the lower plane can be used to move droplets, the upper plate can carry out the necessary chemical and/or biological processes.<ref name="Roux_2007" /> This advantage can be translated into practical experiment protocols in the biological community, such as coupling with DNA amplification.<ref>{{cite journal | vauthors = Coelho B, Veigas B, Fortunato E, Martins R, Águas H, Igreja R, Baptista PV | title = Digital Microfluidics for Nucleic Acid Amplification | journal = Sensors | volume = 17 | issue = 7 | pages = 1495 | date = June 2017 | pmid = 28672827 | pmc = 5539496 | doi = 10.3390/s17071495 | doi-access = free | bibcode = 2017Senso..17.1495C }}</ref><ref name="Kolar_2001" /><ref>{{cite journal | vauthors = Coelho BJ, Veigas B, Bettencourt L, Águas H, Fortunato E, Martins R, Baptista PV, Igreja R | display-authors = 6 | title = Digital Microfluidics-Powered Real-Time Monitoring of Isothermal DNA Amplification of Cancer Biomarker | journal = Biosensors | volume = 12 | issue = 4 | pages = 201 | date = March 2022 | pmid = 35448261 | pmc = 9028060 | doi = 10.3390/bios12040201 | doi-access = free }}</ref> This also allows for the chip to be smaller, and to give researchers more freedom in designing platforms for microdroplet analysis.<ref name="Roux_2007" />