title: Rapid mixing of sub-microlitre drops by magnetic micro-stirring.
abstract: We demonstrate rapid mixing of sub-microlitre droplets (250 nl) using miniaturized magnetic stir bars (400 μm × 200 μm × 15 μm). The stir bars are fabricated using laser micromachining and placed on the substrate on which the drops are manipulated. They are activated by an externally applied magnetic field and used in combination with on-demand drop merging in enthalpy arrays. This technique results in a 10-fold increase in mixing rate, and a mixing time constant of about 2 s. Drop mixing times are measured by Förster resonance energy transfer (FRET) and verified by thermodynamic measurements of binding and enzymatic reactions.
authors.affiliation: Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304, USA. dirk.debruyker@parc.com
authors.forename: Dirk
authors.initials: D
authors.lastname: De Bruyker
authors.forename: Michael I
authors.initials: MI
authors.lastname: Recht
authors.forename: Ali Asgar S
authors.initials: AA
authors.lastname: Bhagat
authors.forename: Francisco E
authors.initials: FE
authors.lastname: Torres
authors.forename: Alan G
authors.initials: AG
authors.lastname: Bell
authors.forename: Richard H
authors.initials: RH
authors.lastname: Bruce
mesh_terms: D031541:Fluorescence Resonance Energy Transfer; D008280:Magnetics; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D008904:Miniaturization; D055585:Physical Phenomena; D013816:Thermodynamics