A method of obtaining protein crystals by filling a glass capillary with a crystallization reagent and a protein sample to form a diffusion pair and allowing them to inter-diffusion has been known for a long time.[1] In the DPOC method, the capillary material is made of water-permeable silicone rubber, and the solution in the DPOC container is osmotically concentrated due to the osmotic pressure difference between the reservoir solution outside the DPOC container and the solution inside. The diffusion phenomenon in the diffusion pair is common to the GT method, but because the amount of the crystallization reagent solution is about the same as that of the protein sample, only the diffusion phenomenon can search for a narrower range of crystallization conditions than the GT method. However, by combining osmotic concentration, a wider range of crystallization condition can be searched.
[1] Salemme, F.R. A free interface diffusion technique for the crystallization of proteins for X-ray crystallography. Arch. Biochem. Biophys. 1972, 151, 533-539.