Light-Driven Formation and Rupture of Droplet Bilayers

Abstract

We demonstrate optical manipulation of nanoliter aqueous droplets containing surfactant or lipid molecules and immersed in an organic liquid using near infrared light. The resulting emulsion droplets are manipulated using both the thermocapillary effect and convective fluid motion. Droplet pair-interactions induced in the emulsion upon optical initiation and control provide direct observations of the coalescence steps in intricate detail. Droplet-droplet adhesion (bilayer formation) is observed under several conditions. Selective bilayer rupture is also realized using the same infrared laser. The technique provides a novel approach to study thin film drainage and interface stability in emulsion dynamics. The formation of stable lipid bilayers at the adhesion interface between interacting water droplets can provide an optical platform to build droplet-based lipid bilayer assays. The technique also has relevance for understanding and improving microfluidics applications by devising Petri dish based droplet assays requiring no substrate fabrication.

Numerical and experimental investigations of the formation process of ferrofluid droplets

“…A single laser spot can increase the formed droplet volume in a cross flowing channel, and switch the droplet transport path at a bifurcation due to laser heating (Baroud et al 2007a, b). The interfacial film dynamics during droplets adhesion because of laser heating was studied by Dixit et al (2010). However, varying droplets size by employing magnetic field was not reported by other research groups.…”

Microfluidic Transport Driven by Opto-Thermal Effects

“…The reversal of optocapillary motion has been reported in several recent studies (Baroud et al, 2007a;Dixit et al, 2010). While poorly understood yet, this reversal is expected to be related to the coupling between thermo-and solutocapillary effects.…”

“…9(b). The subsequent 'remote-controlled' merging is interpreted through the formation of a metastable bilayer surfactant film (Dixit et al, 2010;Kotz et al, 2004). The alternative approach consists in placing the laser spot at the interface that separates two contacting droplets (Baroud et al, 2007b).…”

“…The alternative approach consists in placing the laser spot at the interface that separates two contacting droplets (Baroud et al, 2007b). The bottom panel of Fig Top row: the laser beam pushes a droplet away up to another droplet, then the two droplets coalesce (Dixit et al, 2010). Bottom panel: successive contacting droplets, flowing from the left to the right, are repeatedly merged when the interface is shined (Baroud et al, 2007b).…”

Aqueous droplet manipulation by optically induced Marangoni circulation

“…However, using an optothermal method to manipulate droplets in an immiscible medium in an open chamber can be preferable, as this method limits evaporation, and is capable of moving droplets in arbitrary, reconfigurable trajectories. For example, an infrared laser can be used to induce thermal Marangoni effects at a water/decanol interface, successfully manipulating water droplets (Kotz et al 2004;Dixit et al 2010). However, decanol is toxic, which is an issue if this system is to be used with cells.…”