Abstract
Scale reduction of chemical reactions enables novel screening and synthesis approaches that facilitate a highly parallelized and combinatorial exploration of chemical space. Droplet-based microfluidics have evolved as a powerful platform to allow many chemical reactions within small volumes that each can be controlled and manipulated. A significant technical challenge is the ability to change the concentration of reactants inside a droplet. Here we describe a strategy that relies on the use of reactants that are soluble in both oil and water and allow a passive, diffusive exchange of reactants between the oil and aqueous phases to externally control composition of the droplets. We demonstrate the applicability of our approach by externally changing the pH inside microdroplets without the need for physical manipulation or droplet merging.
Highlights
Scale reduction of chemical reactions enables novel screening and synthesis approaches that facilitate a highly parallelized and combinatorial exploration of chemical space
We describe a strategy that relies on the use of reactants that are soluble in both oil and water and allow a passive, diffusive exchange of reactants between the oil and aqueous phases to externally control composition of the droplets
We demonstrate the applicability of our approach by externally changing the pH inside microdroplets without the need for physical manipulation or droplet merging
Summary
Scale reduction of chemical reactions enables novel screening and synthesis approaches that facilitate a highly parallelized and combinatorial exploration of chemical space. Transport and sorting have made droplet-based microfluidic systems ideal for many applications in synthetic and analytical chemistry[11] Another useful approach is the use of printed microdroplet on a solid support as reaction volumes. By dynamically changing the concentration of reactant in the oil phase, precise control of the concentration of the same reactant within the droplet can be achieved without the need for droplet merging The notion of such a biphasic diffusive exchange was previously used for micro-liquid liquid extraction where two immiscible liquids come into contact and exchange solutes[16]. Of reagents to dispersed droplets via diffusive transport from the continuous phase has been exploited previously to initiate polymerization reactions and to precipitate inorganic materials[17] Even though this strategy has been proven useful to introduce reagents from aqueous phase into oil droplets, the literature on introducing reagents from the water phase to oil phase in a quantitative manner is scarce
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