title: On-site formation of emulsions by controlled air plugs.
abstract: Air plugs are usually undesirable in microfluidic systems because of their detrimental effect on the system's stability and integrity. By controlling the wetting properties as well as the topographical geometry of the microchannel, it is reported herein that air plugs can be generated in pre-defined locations to function as a unique valve, allowing for the on-site formation of various emulsions including single-component droplets, composite droplets with droplet-to-droplet concentration gradient, blood droplets, paired droplets, as well as bubble arrays without the need for precious flow control, a difficult task with conventional droplet microfluidics. Moreover, the self-generated air valve can be readily deactivated (turned off) by the introduction of an oil phase, allowing for the on-demand release of as-formed droplets for downstream applications. It is proposed that the simple, yet versatile nature of this technique can act as an important method for droplet microfluidics and, in particular, is ideal for the development of affordable lab-on-a-chip systems without suffering from scalability and manufacturing challenges that typically confound the conventional droplet microfluidics.
authors.affiliation: Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong, China.
authors.forename: Xiaowen
authors.initials: X
authors.lastname: Huang
authors.forename: Wenli
authors.initials: W
authors.lastname: Hui
authors.forename: Chonglei
authors.initials: C
authors.lastname: Hao
authors.forename: Wanqing
authors.initials: W
authors.lastname: Yue
authors.forename: Mengsu
authors.initials: M
authors.lastname: Yang
authors.forename: Yali
authors.initials: Y
authors.lastname: Cui
authors.forename: Zuankai
authors.initials: Z
authors.lastname: Wang
mesh_terms: D000388:Air; D004655:Emulsions / Q000737:chemistry*; D016650:Fluorescein-5-isothiocyanate / Q000737:chemistry; D005453:Fluorescence; D018922:HL-60 Cells; D006801:Humans; D044085:Microfluidics / Q000379:methods*; D055620:Optical Phenomena
chemical_list: D004655:Emulsions; D016650:Fluorescein-5-isothiocyanate
keywords: droplet microfluidics; immobilization; point of care diagnostics; valve