A magnet-actuated biomimetic device for isolating biological entities in microwells

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.

Analysis of drug–protein interaction in bio-inspired microwells

“…However, the fluorescence signal was observed to weak on plain surfaces as compared to the surfaces with microwells. This observation is in agreement with the previous investigations [18,21]. The surface with microwells confines FITC-BSA in very small volumes in the range of pico to femtolitres, which leads to highly localized intensification of fluorescence signal.…”

“…Oxygen plasma treatment introduces polar functional groups such as silanol group (SiOH) on PDMS surfaces thereby changing its surface behavior from hydrophobic to hydrophilic. In the present work, plasma power was kept constant at 70 W with an oxygen flow rate of 25 sccm, for 120 s. The hydrophilicity of the microwell-surface was retained for 3 h, which was well within the experimental duration of drug-protein interaction [21].…”

“…The surface treatment on PDMSmicrowell surface leads to the complete filling of sample in microwells. The process parameters of OPT were optimized to retain hydrophilicity of PDMS over a long time i.e., 3 h. With the optimal parameters, the change in contact angle on plasma-treated PDMS surface was shown to increase by 12% (from 60° to 68°) over a period of 3 h and 68% (from 60° to 101°) over a period of 6 h. The complete filling of microwells within a minute after placing the sample was confirmed through confocal microscopy measurements [21]. It should be noted that, the experiments to record the fluorescence intensity were conducted within an hour of post-treatment of the microwell-surfaces.…”

“…It should be noted that, the experiments to record the fluorescence intensity were conducted within an hour of post-treatment of the microwell-surfaces. In order to understand the distribution and shape of microwells, twostep lithography was conducted to replicate micropillars from a microwell-surface [21]. Figure 2e shows a crosssectional SEM micrograph of micropillars representing the shape of microwells.…”

Flexible Ferrofluids: Design and Applications

“…Magnetic microfluidics not only inherits systematic precise control over individual fluid and droplet of traditional microfluidics, but also is characterized by simple actuation strategy, flexible controllability, remote operation, as well as noninvasive manipulation ability . Thanks to these superior advantages, magnetic microfluidics is playing a vital role in biomolecule delivery, chemical reactions, bioseparation, polymerase chain reaction (PCR), and many other applications …”