Combining rails and anchors with laser forcing for selective manipulation within 2D droplet arrays

Abstract

We demonstrate the combination of a rails and anchors microfluidic system with laser forcing to enable the creation of highly controllable 2D droplet arrays. Water droplets residing in an oil phase can be pinned to anchor holes made in the base of a microfluidic channel, enabling the creation of arrays by the appropriate patterning of such holes. The introduction of laser forcing, via laser induced thermocapillary forces to anchored droplets, enables the selective extraction of particular droplets from an array. We also demonstrate that such anchor arrays can be filled with multiple, in our case two, droplets each and that if such droplets have different chemical contents, the application of a laser at their interface triggers their merging and a chemical reaction to take place. Finally by adding guiding rails within the microfluidic structure we can selectively fill large scale arrays with monodisperse droplets with significant control over their contents. In this way we make a droplet array filled with 96 droplets containing different concentrations of fluorescent microparticles.

Stationary nanoliter droplet array with a substrate of choice for single adherent/nonadherent cell incubation and analysis

“…Given the ability to generate stationary droplet arrays, we further investigated whether SNDAs may be used to generate stationary droplets, each with a different chemical composition. Such capability was demonstrated before, with other methods (40, 41) using up to 96 stationary droplets (42). Droplets with different chemical composition have the potential to assist in miniaturized high-throughput screening assays, such as testing the influence of a growth factor concentration on cells or antibiotic concentration on bacteria.…”

Droplet Manipulations in Two Phase Flow Microfluidics

“…As is the case with other passive techniques: it is difficult to release the drop once trapped, or to select which way to steer a drop. Using active laser forcing (see Section 3.5) these problems can be overcome [5]. Figure 1.…”

“…This technique has been used for influencing droplet generation, coalescence and fusion [81]. It also has been used in combination with the passive surface energy wells described in Section 2.3 to transport droplets from one rail to another, and to dislodge trapped droplets from their surface energy trap [5].…”

“…A droplet can be pushed out of the well by a consecutive droplet. Adapted from [5] with permission of The Royal Society of Chemistry; (b) Guiding of droplets by electrostatic potential rails. Depending on which electrodes are activated a droplet will be guided towards one of six lateral positions in the channel.…”

“…These methods do not necessarily have to be active. Some elegant passive methods have been developed for splitting [3,4], guiding [5] and trapping [5][6][7] drops at a certain location. Thirdly, most protocols require a certain type of analysis or detection, which mostly is optical (scattering, transmission, adsorption, fluorescence, Raman, surface plasmon resonance) or electrical (measuring current, voltage, impedance).…”