Ultrafast microfluidic mixer with three-dimensional flow focusing for studies of biochemical kinetics

Abstract

Studies of the kinetics of biochemical reactions, especially of folding of proteins and RNA, are important for understanding the function of biomolecules and processes in live cells. Many biochemical reactions occur rapidly and thus need to be triggered on very short time scales for their kinetics to be studied, which is often accomplished by mixing in a turbulent flow. More rapid and sample-efficient mixing is achieved in laminar flow in a microfluidic device, in which the sample is two-dimensionally (2D) focused to a thin sheet. Here we describe the design and operation of an ultrafast microfluidic mixer with three-dimensional (3D) flow focusing. The confinement of a 3D-focused sample to a narrow stream near the middle of a microchannel renders its velocity nearly uniform and makes it possible to monitor the reaction kinetics without exclusion of any parts of the sample. Hence, the sample consumption is substantially reduced and the fluorescence of the sample can be monitored without a confocal setup. Moreover, the 3D-focusing allows facile measurements of velocity of the sample with a high spatial resolution using a specially developed technique based on epi-fluorescence imaging. The data on the velocity vs. position are used to precisely calibrate the conversion between position and the reaction time, which is essential for accurate kinetic measurements. The device performs mixing on a 10 ms scale, which is comparable to that of the laminar mixers with 2D focusing. Unlike previous ultrafast laminar mixers, which were machined in hard materials, the present microfluidic device is made of a single cast of poly(dimethylsiloxane), PDMS, and is thus simpler and less expensive to manufacture.

Analysis of a laminar-flow diffusional mixer for directed self-assembly of liposomes

“…10,11 It additionally provides control of the shape of the interface between converging solutions, 12 of the concentration distributions and gradients, and of the residence times of the solutes. 13 Size and geometry of microfluidic channel influence the size distribution of the resulting liposomes.…”

“…19 Hydrodynamic focusing forms an integral part of a typical laminar-flow diffusionmixer. 5,6,13,[20][21][22][23] The technique uses co-flow of miscible focusing solution to confine a solution to a sub-cross-section of a channel. Groups develop various hydrodynamic focusing architectures for mitigating sticking to channel walls, 6 ensuring rapid mixing, 13,24,25 and ensuring uniform residence time among the focused solutes.…”

“…5,6,13,[20][21][22][23] The technique uses co-flow of miscible focusing solution to confine a solution to a sub-cross-section of a channel. Groups develop various hydrodynamic focusing architectures for mitigating sticking to channel walls, 6 ensuring rapid mixing, 13,24,25 and ensuring uniform residence time among the focused solutes. 13,21,22 Three-dimensional (3D) hydrodynamic focusing sheaths a solution into a cylindrical core at the center of the channel, whereas twodimensional (2D) hydrodynamic focusing sheaths a solution into a columnar shape spanning the height of the channel.…”

A simple and efficient outflow boundary condition for the incompressible Navier–Stokes equations

“…There is also much research into sophisticated three-dimensional hydrodynamics and pollutant modelling (Chau & Jiang, 2001, 2004Epely-Chauvin, De Cesare, & Schwindt, 2014;Gholami, Akbar, Minatour, Bonakdari, & Javadi, 2014;Liu & Yang, 2014;Wu & Chau, 2006). Thus, microfluidics has become important for many lab-on-a-chip applications such as enzymatic kinetics (Pabit & Hagen, 2002), protein folding (Gambin, Simonnet, VanDelinder, Deniz, & Groisman, 2010), single molecule detection (De Mello & Edel, 2007), and flow cytometry (Mao, Lin, Dong, & Huang, 2009;Wang et al, 2005;Yun et al, 2010). The aspect ratio of a typical micro-channel is very large.…”

Ultrafast cooling reveals microsecond-scale biomolecular dynamics

“…To rapidly exchange the medium, microfluidic devices with tight hydrodynamic focusing of a narrow stream of protein solution in a continuous laminar flow have been used, reaching temporal resolutions as high as B1 ms 1,2 . Microfluidic systems require small sample volumes and are compatible with high-resolution optical microscopy, making them well suited for experiments with fluorescently labelled biomolecules 3,4 . Nevertheless, hydrodynamic focusing systems require delicate adjustment and careful measurements of high-speed microscopic flows, complicating their practical application.…”