Fig. 6. Mineral shells formed from [W/O/W] double emulsions support in vitro protein expression.

(A) Schematic overview of the second, double emulsion–producing, flow-focusing junction of a two-junction flow-focusing microfluidic device used to generate mineralized double emulsions (see fig. S10 and movie S4). (B) Schematic of [W/O/W] droplet mineralization to form an interfacial mineral layer around bacterial extracts in the innermost water phase. Here, “S” is a fluorogenic substrate (CCF2) that changes emission properties when enzymatically converted to product (“P”) by β-lactamase (β-lac) enzyme. (C) Polarized light optical micrograph shows interfacial birefringence. (D) Flow cytometry scatter plots of 50,000 droplets, proving that mineralized droplets support compartmentalized in vitro protein expression.