A novel technique to control the rate of vapour diffusion, giving larger protein crystals

The process of protein crystallization often takes place too rapidly, thus producing showers of crystals instead of large single crystals. A novel technique for improving protein-crystal size by slowing down the crystallization process is described. This is achieved by the setting up of a vapour-diffusion experiment with a layer of oil placed above the reservoir. The oil acts as a barrier between the reservoir and the crystallization drop, but water vapour diffuses slowly through the layer of oil. The type of oil and the thickness of the oil layer situated above the reservoir will dictate the rate of vapour diffusion and consequently the speed of crystallization. This technique reduces the number of crystals grown and increases their size.