Microfluidic device for protein crystallization under controlled humidity

Crystallization is one of the key steps for the determination of a protein structure by X-ray diffraction. Microfluidics offers new perspectives for high throughput screening of the crystallization conditions with much reduced cost. In particular, fast prototyping of microfluidic devices by soft-lithography using PDMS has lead to successful demonstrations of both on chip crystallisation and large scale integration. However, PDMS, which is gas permeable, can lead irreversibly to the liquid evaporation in microfluidic chambers. Because of the fragility of the protein crystals, this is clearly undesirable for post-crystallization experiments. We describe here a simple but yet efficient approach to solve this problem, where the PDMS device is placed inside a small tight box having two compartments separated with a thin membrane. Inside the box, a good control of humidity can be achieved and protein crystals could be conserved over a long period without dehydratation. (c) 2007 Elsevier B.V. All rights reserved.