title: Comprehensive two-dimensional manipulations of picoliter microfluidic droplets sampled from nanoliter samples.
abstract: A facile method is presented for achieving comprehensive two-dimensional droplet manipulations in closed microstructures consisting of microwell arrays and a straight microchannel. In this method, picoliter/nanoliter droplets with controllable sizes and numbers are sampled from nanoliter samples/reagents with almost 100% efficiency. Droplet motions are precisely controlled in the ±X-direction and ±Y-direction by managing hydrostatic pressure and magnetic repulsion, respectively. As a demonstration, a fluorescein-labeled droplet and a deionized droplet are successively generated and trapped in adjacent microwells. Then their positions are quickly exchanged without cross-contamination and fusion is implemented on-demand. After operations, hydrophobic ferrofluid can be completely replaced by mineral oil and droplets still remain in microwells safely. A typical fluorescence intensity-based assay is demonstrated: droplet arrays containing copper ion are diluted disproportionately first and then detected by addition of droplet arrays containing Calcein. With the ability of comprehensive two-dimensional droplet manipulations, this method could be used in various miniaturized biochemical analyses including requirements of multistep procedures and in situ monitoring.
authors.affiliation: School of Pharmacy, East China University of Science and Technology, Shanghai 200237, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Zhang
authors.forename: Qionglin
authors.initials: Q
authors.lastname: Liang
authors.forename: Xiaoni
authors.initials: X
authors.lastname: Ai
authors.forename: Ping
authors.initials: P
authors.lastname: Hu
authors.forename: Yiming
authors.initials: Y
authors.lastname: Wang
authors.forename: Guoan
authors.initials: G
authors.lastname: Luo
mesh_terms: D003300:Copper / Q000032:analysis; D004129:Dimethylpolysiloxanes / Q000737:chemistry; D019793:Fluorescein / Q000737:chemistry; D005452:Fluoresceins / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D046228:Microarray Analysis; D046210:Microfluidic Analytical Techniques; D008899:Mineral Oil / Q000737:chemistry; D036103:Nanotechnology
chemical_list: D004129:Dimethylpolysiloxanes; D005452:Fluoresceins; D007477:Ions; C013830:baysilon; D003300:Copper; D008899:Mineral Oil; D019793:Fluorescein; C007740:fluorexon