title: Achieving uniform mixing in a microfluidic device: hydrodynamic focusing prior to mixing.
abstract: We describe a microfluidic mixer that is well-suited for kinetic studies of macromolecular conformational change under a broad range of experimental conditions. The mixer exploits hydrodynamic focusing to create a thin jet containing the macromolecules of interest. Kinetic reactions are triggered by molecular diffusion into the jet from adjacent flow layers. The ultimate time resolution of these devices can be restricted by premature contact between co-flowing solutions during the focusing process. Here, we describe the design and characterization of a mixer in which hydrodynamic focusing is decoupled from the diffusion of reactants, so that the focusing region is free from undesirable contact between the reactants. Uniform mixing on the microsecond time scale is demonstrated using a device fabricated by imprinting optical-grade plastic. Device characterization is carried out using fluorescence correlation spectroscopy (FCS) and two-photon microscopy to measure flow speeds and to quantify diffusive mixing by monitoring the collisional fluorescence quenching, respectively. Criteria for achieving microsecond time resolution are described and modeled.
authors.affiliation: School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Hye Yoon
authors.initials: HY
authors.lastname: Park
authors.forename: Xiangyun
authors.initials: X
authors.lastname: Qiu
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Rhoades
authors.forename: Jonas
authors.initials: J
authors.lastname: Korlach
authors.forename: Lisa W
authors.initials: LW
authors.lastname: Kwok
authors.forename: Warren R
authors.initials: WR
authors.lastname: Zipfel
authors.forename: Watt W
authors.initials: WW
authors.lastname: Webb
authors.forename: Lois
authors.initials: L
authors.lastname: Pollack
mesh_terms: D044085:Microfluidics / Q000295:instrumentation*; D008962:Models, Theoretical; D013057:Spectrum Analysis / Q000379:methods