Nanoliter dispensing method by degassed poly(dimethylsiloxane) microchannels and its application in protein crystallization.

This paper describes a method of dispensing a nanoliter volume of liquid into arrays of microwells through degassed poly(dimethylsiloxane) (PDMS) microchannels. In this method, the PDMS microchannels were reversibly bound to arrays of microwells. The PDMS elastomer was predegassed and served as an internal vacuum pumping source. Various aqueous solutions were infused into arrays of microwells through the reversibly sealed PDMS microchannels. Microwells fabricated in PDMS, poly(methyl methacrylate) (PMMA), and glass were all compatible with this dispensing method. By removing the PDMS microchannels, arrays of droplets confined in the microwells were obtained. Multiplex reaction and screening at the nanoliter scale were carried out by binding two such arrays of microwells to form microchambers. We applied this method to screening the crystallization conditions of four known proteins. Long-term incubation of over 2 months was achieved by employing glass microwells. An unknown protein was then crystallized using the screening method in microwells. The crystals with sufficient size were harvested from the reversibly bound microwells. X-ray diffraction with a resolution of 3.1 Angstrom was obtained.