Abstract
We employ the PhaseChip, a (poly)dimethylsiloxane (PDMS) microfluidic device, for statistical studies of protein crystal nucleation. The PhaseChip is designed to decouple nucleation and growth of protein crystals and so improve their yield and quality. Two layers of fluidic channels containing salt reservoirs and nanoliter-sized wells for protein drops in oil are separated by a thin PDMS membrane, which is permeable to water, but not to salt or macromolecules such as protein. We reversibly vary the supersaturation of protein inside the stored droplets by controlling the chemical potential of the reservoir. Lysozyme in the presence of sodium chloride is used as a model system. We determine the crystal nucleation rate as a function of protein supersaturation by counting the number of crystal nuclei per droplet, as demonstrated by Galkin and Vekilov.1.