Open Space Diffusive Filter for Simultaneous Species Retrieval and Separation

Microfluidic Aqueous Two-Phase Focusing of Chemical Species for In Situ Subcellular Stimulation

Confinement of chemical species in a controllable micrometer-level (several to a dozen micrometers) space in an aqueous environment is essential for precisely manipulating chemical events in subcellular regions. However, rapid diffusion and hard-to-control micrometer-level fluids make it a tough challenge. Here, a versatile open microfluidic method based on an aqueous two-phase system (ATPS) is developed to restrict species inside an open space with micron-level width. Unequal standard chemical potentials of the chemical species in two phases and space-time correspondence in the microfluidic system prevent outward diffusion across the phase interface, retaining the target species inside its preferred phase flow and creating a sharp boundary with a dramatic concentration change. Then, the chemical flow (the preferred phase with target chemical species) is precisely manipulated by a microfluidic probe, which can be compressed to a micron-level width and aimed at an arbitrary position of the sample. As a demonstration of the feasibility and versatility of the strategy, chemical flow is successfully applied to subcellular regions of various kinds of living single cells. Subcellular regions are successfully labeled (cytomembrane and mitochondria) and damaged. Healing-regeneration behaviors of living single cells are triggered by subcellular damage and analyzed. The method is relatively general regarding the species of chemicals and biosamples, which could promote deeper cell research.

Microscale hydrodynamic confinements: shaping liquids across length scales as a toolbox in life sciences

Hydrodynamic phenomena can be leveraged to confine a range of biological and chemical species without needing physical walls. In this review, we list methods for the generation and manipulation of microfluidic hydrodynamic confinements in free-flowing liquids and near surfaces, and elucidate the associated underlying theory and discuss their utility in the emerging area of open space microfluidics applied to life-sciences. Microscale hydrodynamic confinements are already starting to transform approaches in fundamental and applied life-sciences research from precise separation and sorting of individual cells, allowing localized bio-printing to multiplexing for clinical diagnosis. Through the choice of specific flow regimes and geometrical boundary conditions, hydrodynamic confinements can confine species across different length scales from small molecules to large cells, and thus be applied to a wide range of functionalities. We here provide practical examples and implementations for the formation of these confinements in different boundary conditions - within closed channels, in between parallel plates and in an open liquid volume. Further, to enable non-microfluidics researchers to apply hydrodynamic flow confinements in their work, we provide simplified instructions pertaining to their design and modelling, as well as to the formation of hydrodynamic flow confinements in the form of step-by-step tutorials and analytical toolbox software. This review is written with the idea to lower the barrier towards the use of hydrodynamic flow confinements in life sciences research.

An Open Microfluidic Chip for Continuous Sampling of Solute from a Turbulent Particle Suspension

High solids content complicates in situ analysis of chemical processing, biological suspensions, and environmental streams. In most cases, analytical methods require at least one pre-treatment step of a small volume of sample before a particle-free fluid can be analyzed. We have developed a continuous in situ sampler that can "sip" particle-free solution from a turbulent high solids content stream (a slurry). An open microfluidic chip with an extended slit opening shields the internal laminar flow from the turbulence outside. Unlike other open chips, our chip does not require close proximity to a solid surface and operates in turbulent environments for hours without maintenance. Two applications are demonstrated: monitoring Fe^III in a stirred slurry of mixed ore particles at high solids loading (4 %wt) and paracetamol tablet dissolution profiles for two different formulations.