This paper describes a microfabrication process for constructing three-dimensional microfluidic structures in polydimethylsiloxane (PDMS). Rapid prototyping of microfluidic devices is possible starting from ink-jet printed masks and by utilising replica molding to create fluidic structures in PDMS from SU-8 and SPR-220 masters pre-patterned on a silicon or glass substrate. Multi-layer bonded and stacked alignment of up to 13 different functional polymer microfluidic layers with through-layer fluidic interconnects has been demonstrated. Pneumatically actuated valves have also been demonstrated for the regulation of sub-10 nL of fluid volumes. The geometric design of the valves is described with experimental verification conducted on rounded and vertical channel profiles to examine the effects of channel geometry on valve leak rates. The PDMS-based technology allows for the fabrication of devices with extremely small reaction volumes and parallel sample processing, making these devices ideally suited to applications which require high throughput processing and the ability to conduct parallel assays with very limited volumes of reagent and sample. We describe the applications of this technology to protein crystallization in particular.

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