Microfluidics for Nucleation Rates and in situ X-Ray

by Prof. Seth Fraden (Brandeis University)

Tuesday 9 Apr 2013, 14:00 → 16:00 Europe/Rome

Aula 5 (Dipartimento di Fisica - Ed. G. Marconi)

The transformation of a protein solution to a crystal is governed by two non-equilibrium processes; nucleation and growth. Consequently, supersaturation kinetics plays an essential role in crystallization and the optimal crystallization strategy should screen kinetic trajectories involving variables such as depth of supersaturation, duration of supersaturation, sample volume and addition of nucleants. We have developed a technology based on emulsion microfluidics in which 1 nl drops of protein solution are encapsulated in oil and stabilized by surfactant. Crystallization is a stochastic process; we determine nucleation rates by measuring induction times in thousands of identical drops. Surprisingly complex, but reproducible and systematic behavior is observed for lysozyme / PEG mixtures suggestive of 2-step processes in contrast to classical nucleation theory. Porous silica acts as heterogeneous nucle! ation centers and enhances nucleation rates. For the protein lysozyme we find porous silica preferentially increases the occurrence of one of two polymorphs. The functional form of the nucleation kinetics suggests nucleation of each polymorph occurs through fundamentally different mechanisms.