Protein crystallization free interface diffusion

Hansen CL, Skordalakes E, Berger JM, Quake SR (2002) A robust and scalable microfluidic metering method that allows protein crystal growth by free interface diffusion. Proc Natl Acad Sci USA 99 16531-16536 Herzig-Marx R, Queeney KT, Rebecca JJ, Schmidt MA, Jensen KF (2004) Infrared spectroscopy for chemically specific sensing in silicon-based microreactors. Anal Chem 76 6476-6483... 

A microfluidic chip has been developed for rapid screening of protein crystallization conditions (Hansen et al., 2002) using the free interface diffusion method. The chip is comprised of a multilayer, silicon elastomer and has 480 valves operated by pressure. The valves are formed at the intersection of two channels separated by a thin membrane. When pressure is applied to the top channel it collapses... 

Hansen, C. L., et ah, A robust and scalable microfluidic metering method that allows protein crystal growth by free interface diffusion. PNAS 2002, 99, 16531— 16536. 

Salemme, F.R., A free interface diffusion technique for the crystallization of proteins for X-ray crystallography. Arch. Bio-chem. Biophys. 1972, 151. 

There are other techniques, however, including microbatch crystallization, where the protein and precipitant are just mixed at the final supersaturation concentration. Free interface diffusion is similar to microbatch but the two components have to diffuse toward each other the concentrations of both protein and precipitant therefore vary with distance from the original interface. In microdialysis, the precipitant solution is allowed to equilibrate with the protein solution through a semipermeable membrane, which permits passage of the precipitant but not the protein (Figure 7). Of these techniques, the first two also lend themselves to automation. 

Figure 12.20 The free interface diffusion method utilizes a capillary to minimize convective mixing between the protein solution and the second layer of solution containing the crystallization agent (e.g., salt or PEG). The capillary is sealed at both ends with an appropriate adhesive or wax to prevent evaporation of the solution.

---