Programmable protein crystallization in metered encapsulated droplets

We report for the first time programmable protein crystallization based on tunable evaporation and dissolution of salt and protein precipitants of an aqueous core droplet encapsulated in an oil shell. The evaporation depended on the precisely metered aqueous and oil droplet volumes and the position of the aqueous core droplet. The dissolution of the precipitants was achieved by adjusting the temperature of the aqueous core droplet. Lysozyme protein crystal was obtained within 80 min through (1) rapid salt/protein precipitation by fast evaporation, (2) salt dissolution by heating to enhance protein crystallization, and (3) protein crystallization from the protein precipitants (seeds) by slow evaporation.