Droplet-based microfluidic washing module for magnetic particle-based assays

Abstract

In this paper, we propose a continuous flow droplet-based microfluidic platform for magnetic particle-based assays by employing in-droplet washing. The dropletbased washing was implemented by traversing functionalized magnetic particles across a laterally merged droplet from one side (containing sample and reagent) to the other (containing buffer) by an external magnetic field. Consequently, the magnetic particles were extracted to a parallel-synchronized train of washing buffer droplets, and unbound reagents were left in an original train of sample droplets. To realize the droplet-based washing function, the following four procedures were sequentially carried in a droplet-based microfluidic device: parallel synchronization of two trains of droplets by using a ladder-like channel network; lateral electrocoalescence by an electric field; magnetic particle manipulation by a magnetic field; and asymmetrical splitting of merged droplets. For the stable droplet synchronization and electrocoalescence, we optimized droplet generation conditions by varying the flow rate ratio (or droplet size). Image analysis was carried out to determine the fluorescent intensity of reagents before and after the washing step. As a result, the unbound reagents in sample droplets were significantly removed by more than a factor of 25 in the single washing step, while the magnetic particles were successfully extracted into washing buffer droplets. As a proof-of-principle, we demonstrate a magnetic particle-based immunoassay with streptavidin-coated magnetic particles and fluorescently labelled biotin in the proposed continuous flow dropletbased microfluidic platform. V C 2014 AIP Publishing LLC.

High-throughput magnetic particle washing in nanoliter droplets using serial injection and splitting

“…6d). Comparable approaches achieved a 25-fold reduction in concentration of input solution albeit at much lower throughput ~ 2 Hz and with multiple reported failure mechanisms [22]. Wash efficiency in this work could be improved through a number of approaches.…”

K-Channel: A Multifunctional Architecture for Dynamically Reconfigurable Sample Processing in Droplet Microfluidics

“…19,35,36 Finally, common biochemical techniques like ELISA typically require washing samples on a solid phase like antibody-conjugated magnetic beads, 37 but only limited efforts have demonstrated analogous processes in continuously flowing droplets at low throughput (1–5 droplets per second) compared to many other droplet operations (100–1000 droplets per second). 38,39 Therefore, the clear need exists to engineer versatile and robust droplet manipulation modules that simplify assay optimization and enable in-droplet washing.…”

“…6,42 Other variations on cross-channel flow interfaced to droplets have been specialized to single operations. 38,43 …”

“…19,35 Finally, we demonstrate the versatility of the K-channel module to create a two-step washing device consisting of magnetic bead-concentrating droplet splitting followed by water injection, and realize robust device operation at nearly two orders of magnitude higher droplet frequency than previous reports. 38,39 …”

Intra-droplet acoustic particle focusing: simulations and experimental observations

“…To control the position of particles inside droplets both active and passive methods have been implemented including magnetophoresis (Lombardi and Dittrich 2011;Lee et al 2014;Brouzes et al 2015), dielectrophoresis (Han et al 2017), acoustophoresis (Fornell et al 2015Park et al 2017) and hydrodynamic methods (Kurup and Basu 2012;Sun et al 2012;Hein et al 2015). Of these, acoustophoresis has the advantages of being label free, gentle, and operated in non-contact mode.…”