The use of microwells is popular for a wide range of applications due to its’ simplicity. However, the seeding of conventional microwells, which are closed at the bottom, is restricted to gravitational sedimentation for cell or particle deposition and therefore require lengthy settling times to maximize well occupancy. The addition of microfluidics to the capture process has accelerated cell or particle dispersion and improved capture ability but is mostly limited to gravitationally-driven settling for capture into the wells. An alternative approach to conventional closed-microwells, sieved microwells supersedes reliance on gravity by using hydrodynamic forces through the open pores at the bottom of the microwells to draw targets into the wells. We have developed a rapid fabrication method, based on flow lithography techniques, which allows us to easily customize the mesh pore sizes in a simple two-step process. Finally, by combining this microwell design with cross-flow trapping in a microfluidic two-layered channel, we achieve an 88 ± 6% well occupancy in under 10 s.

diagnostics, [6] biomolecule evolution, [7] and food-grade quality control. [8] These applications use monodispersed picoliteror nanoliter-volume droplets, resulting in cost-effective and time-efficient procedures. [9] Classical microdroplet formation methods to form such microdroplets use oil and water as immiscible liquids. Oil, however, is a non-biocompatible medium that must be removed subsequent to droplet formation because the oil phase negatively impacts on encapsulated biological species, such as cells, in the water droplet phase. Thus, an additional step, typically a time-and labor-intensive oilremoval treatment, would be required. [10] Alternatively, aqueous two-phase systems (ATPSs) have recently made a high-impact appearance in the droplet formation field because of its biocompatibility. The applicability of ATPS as a medium for cells and biomolecules has been widely proven, allowing for it to be a reasonable option for biological applications and, furthermore, the elimination of post-processing washing. [11] ATPSs have been applied to partitioning and purification of proteins, [12] enzymes, [13,14] drug residues in food and water, [15,16] etc., as well as cell patterning [17] and fractionation. [18] There are many unique ATPS compositions available for implementation including, but not limited to, polymer-salt [19,20] and alcohol-salt. [21,22] The mixture of polyethylene glycol (PEG) and dextran (DEX) is a well-documented polymerpolymer composition that has been often-used for droplet formation. [23] The main challenge in the ATPS droplet formation is overcoming the ultra-low interfacial tension (< 1 mJ m −2 ) [24] of the two aqueous-phases making hydrodynamic thread break-up difficult and restricted to jetting droplet regimes. [25] For successful droplet break-up, active methods use external forces to overcome the viscous forces that stretch the interface between the aqueous continuous and dispersed phases. Active approaches thus require external components for flow perturbation, such as, piezo-electric disc actuation, [26,27] mechanical vibration, [28,29] inlet pressure pulsation, [30] and pneumatic valve control. [31] Recent passive approaches in flow focusing microfluidic platforms simplify the droplet formation mechanism by eliminating external component requirements. Passive methods canThe generation of water-in-water droplets has recently received great attention for its applicability in biological applications over traditional oil-water droplet systems because of their high biocompatibility. An aqueous twophase system (ATPS), aqueous mixture of polyethylene glycol (PEG) and dextran (DEX), has an ultra-low interfacial tension which makes monodispersed droplet formation challenging. Recent passive methods in microfluidics with flow-focusing configurations overcome this challenge, but they suffer either from polydispersity, narrow droplet size range, or low throughput. Successful droplet formation in such passive methods occurs in jetting flow regimes with low continuous phase flowrates, Q c < ...

Hydrogel‐based biosensing, based on antigen–antibody binding, has been utilized for various biomedical applications such as cancer monitoring. Hydrogels offer highly sensitive detection with the prevention of nonspecific binding because of 3D porous structure and hydrophilicity. However, these hydrogel‐based biosensing platforms require a time scale of hours to complete immunoassays because binding events are diffusion‐limited, where target biomolecules must diffuse into and throughout the 3D porous network. Here, a new rapid microfluidic platform is introduced utilizing a cross‐flow induced advective‐transportation of targets into a hydrogel membrane with fluorescent reporting. This flow enhanced delivery of target analytes significantly reduces their detection time to under 15 min. This flow effect is also numerically investigated on the detection process. Both numerical and experimental results show an exponential decrease in the detection time. More importantly, the cross‐flow configuration in our platform provides an additional size‐based filtration feature that effectively selects against larger components in a blood sample, such as red blood cells, during the detection process. This addition, not seen in conventional biosensing platforms, eliminates the need for blood sample prefiltration.