title: Electrohydrodynamic generation and delivery of monodisperse picoliter droplets using a poly(dimethylsiloxane) microchip.
abstract: We developed a drop-on-demand microdroplet generator for the discrete dispensing of biosamples into a bioanalytical unit. This disposable PDMS microfluidic device can generate monodisperse droplets of picoliter volume directly out of a plane sidewall of the microfluidic chip by an electrohydrodynamic mechanism. The droplet generation was accomplished without using either an inserted capillary or a monolithically built-in tip. The minimum droplet volume was approximately 4 pL, and the droplet generation was repeatable and stable for at least 30 min, with a typical variation of less than 2.0% of drop size. The Taylor cone, which is usually observed in electrospray, was suppressed by controlling the surface wetting property of the PDMS device as well as the surface tension of the sample liquids. A modification of the channel geometry right before the opening of the microchannel also enhanced the continuous droplet generation without applying any external pumping. A simple numerical simulation of the droplet generation verified the importance of controlling the surface wetting conditions for the droplet formation. Our microdroplet generator can be effectively applied to a direct interface of a microfluidic chip to a biosensing unit, such as AMS, MALDI-MS or protein microarray-type biochips.
authors.affiliation: Department of Electrical Engineering and Computer Science, Biological Engineering Division, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
authors.forename: Sung Jae
authors.initials: SJ
authors.lastname: Kim
authors.forename: Yong-Ak
authors.initials: YA
authors.lastname: Song
authors.forename: Paul L
authors.initials: PL
authors.lastname: Skipper
authors.forename: Jongyoon
authors.initials: J
authors.lastname: Han
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D004583:Electrons; D057927:Hydrophobic and Hydrophilic Interactions; D046208:Microchip Analytical Procedures / Q000379:methods*; D014867:Water / Q000737:chemistry*
chemical_list: D004129:Dimethylpolysiloxanes; D014867:Water