Summary We describe a spraying-plunging method for preparing cryo-EM grids with vitreous ice of controllable, highly consistent thickness using a microfluidic device. The new polydimethylsiloxane (PDMS)-based sprayer was tested with apoferritin. We demonstrate that the structure can be solved to high resolution with this method of sample preparation. Besides replacing the conventional pipetting-blotting-plunging method, one of many potential applications of the new sprayer is in time-resolved cryo-EM, as part of a PDMS-based microfluidic reaction channel to study short-lived intermediates on the time-scale of 10 to 1000 ms.

Continuous dielectrophoretic separation is recognized as a powerful technique for a large number of applications including early stage cancer diagnosis, water quality analysis, and stem-cell-based therapy. Generally, the prefocusing of a particle mixture into a stream is an essential process to ensure all particles are subjected to the same electric field geometry in the separation region. However, accomplishing this focusing process either requires hydrodynamic squeezing, which requires an encumbering peripheral system and a complicated operation to drive and control the fluid motion, or depends on dielectrophoretic forces, which are highly sensitive to the dielectric characterization of particles. An alternative focusing technique, induced charge electro-osmosis (ICEO), has been demonstrated to be effective in focusing an incoming mixture into a particle stream as well as nonselective regarding the particles of interest. Encouraged by these aspects, we propose a hybrid method for microparticle separation based on a delicate combination of ICEO focusing and dielectrophoretic deflection. This method involves two steps: focusing the mixture into a thin particle stream via ICEO vortex flow and separating the particles of differing dielectic properties through dielectrophoresis. To demonstrate the feasibility of the method proposed, we designed and fabricated a microfluidic chip and separated a mixture consisting of yeast cells and silica particles with an efficiency exceeding 96%. This method has good potential for flexible integration into other microfluidic chips in the future.

It is difficult to mix two liquids on a microfluidic chip because the small dimensions and velocities effectively prevent the turbulence. This paper describes two 2-layer PDMS passive micromixers based on the concept of splitting and recombining the flow that exploits a self-rotated contact surface to increase the concentration gradients to obtain fast and efficient mixing. The designed micromixers were simulated and the mixing performance was assessed. The mixers have shown excellent mixing efficiency over a wide range of Reynolds number. The mixers were reasonably fabricated by multilayer soft lithography, and the experimental measurements were performed to qualify the mixing performance of the realized mixer. The results show that the mixing efficiency for one realized mixer is from 91.8% to 87.7% when the Reynolds number increases from 0.3 to 60, while the corresponding value for another mixer is from 89.4% to 72.9%. It is rather interesting that the main mechanism for the rapid mixing is from diffusion to chaotic advection when the flow rate increases, but the mixing efficiency has not obvious decline. The smart geometry of the mixers with total length of 10.25 mm makes it possible to be integrated with many microfluidic devices for various applications in l-TAS and Lab-on-a-chip systems. V C 2013 AIP Publishing LLC.

Microfluidically generated double emulsions are promising templates for microreactions, which protect the reaction from external disturbance and enable in vitro analyses with large-scale samples. Controlled combination of their inner droplets in a continuous manner is an essential requirement toward truly applications. Here, we first generate dual-cored double-emulsion drops with different inner encapsulants using a capillary microfluidic device; next, we transfer the emulsion drops into another electrode-integrated polydimethylsiloxane microfluidic device and utilize external AC electric field to continuously trigger the coalescence of inner cores inside these emulsion drops in continuous flow. Hundreds of thousands of monodisperse microreactions with nanoliter-scale reagents can be conducted using this approach. The performance of core coalescence is investigated as a function of flow rate, applied electrical signal, and core conductivity. The coalescence efficiency can reach up to 95%. We demonstrate the utility of this technology for accommodating microreactions by analyzing an enzyme catalyzed reaction and by fabricating cell-laden hydrogel particles. The presented method can be readily used for the controlled triggering of microreactions with high flexibility for a wide range of applications, especially for continuous chemical or cell assays.