Abstract
Microwell platforms show great promise in single-cell studies and protein measurements because of their low volume sampling, rapid analysis and high throughput screening ability. However, the existing actuation mechanisms to manipulate the target samples and fabrication procedures involved in the microwell-based microfluidic devices are complex, resource-intensive and require an external power source. In this work, we present proof of concept of a simple, power-free and low-cost closed magnet digital microfluidics device for isolating biological entities in femtoliter-sized microwells. The target biological entities were encapsulated in magnetic liquid marbles and shuttled back and forth between micropatterned top and bottom plates in the microdevice to obtain high loading efficiency and short processing time. The microdevice performance was studied through fluorescent detection of three different entities: microbeads, bovine serum albumin (BSA) and Escherichia coli, captured in the microwell array. Almost 80% of the microwells were loaded with single microbeads in five shuttling cycles, in less than a minute. Further, a low volume of BSA was compartmentalized in the microwell array over a two order range of concentration. The microdevice exhibits two unique features: lotus leaf stamps were used to fabricate micropatterns (microwells and micropillars) on top and bottom plates to impart functionality and cost-effectiveness, and the target samples were actuated by a permanent magnet to make the microdevice power-free and simple in operation. The developed biomimetic microdevice is therefore capable of capturing a multitude of biological entities in low-resource settings.
Highlights
Magnetic digital microfluidics is emerging as a potential choice for point-of-care applications due to its unique advantages over other digital microfluidic (DMF) techniques such as electrowetting-on-dielectric (EWOD), surface acoustic wave and light-driven[1]
The closed EWOD-based DMF platforms were successfully employed in isolation of bio-entities such as proteins and cells[8,9,10]
Witters et al.[9] demonstrated the functioning of a closed EWOD-based DMF platform to isolate streptavidin-coated superparamagnetic beads in microwells assisted by a permanent magnet, to detect single molecules of biotinylated β-galactosidase
Summary
A simple low-cost microdevice for isolating biological entities in microwell is proposed in this work (Fig. 1A,B). The microwells on the top plate were used to capture the biological entities, which were encapsulated in the magnetic liquid marble (see Fig. 1C). Micropillars on the bottom plate reduce the frictional force, thereby responsible for smooth movement of the magnetic liquid marble In this microdevice, the surface topography of naturally available lotus leaf was exploited to prepare surfaces containing microwells and micropillars as shown in Fig. 1A (inset). Characterization of the as-synthesized Fe3O4 nanoparticles for their size, shape and magnetic behaviour is presented This is followed by an analysis of the morphology and wettability of plain and textured PDMS surfaces. Surface with micropillars exhibited a higher degree of hydrophobicity than the surface with microwells
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