Suppressing internal convection of a droplet using confinement during protein crystallization

Abstract

Fluid convection during protein crystallization plays a significant role in determining the crystal growth rate and crystal quality. Crystals grown in reduced flow strength gives a superior quality crystal. Hence, tuning the fluid flow strength is very essential in the crystal growth process. In this work, we demonstrate a new method to suppress the flow strength using the confinement effect during the vapor diffusion method of protein crystallization where the crystal is grown inside an evaporating droplet. A flow study is carried out at four different confinement conditions to study the effect of confinement. The flow inside the droplet is caused by the evaporation induced natural convection, which is measured by the micro-PIV method. The concentration gradient generated around the growing crystal induces buoyancy driven flow around the protein crystal during the crystal growth phase. The evaporation rate from the droplet and the flow strength inside the droplet get suppressed by increasing the confinement. Hence, the flow strength can be tuned by adjusting the confinement, which is a very simple method to manipulate the flow strength inside the protein droplet.