Controlling microdrop shape and position for biotechnology using micropatterned rings

Photolithographic micropatterning is used to achieve topographic rather than chemical control of the static shape and position of microdrops on solid substrates in a gaseous ambient. Micrometer cross-section, millimeter-diameter circular rings with steep sidewalls strongly and robustly pin contact lines of nanoliter to 100 μl liquid drops, increasing the maximum stable drop volume and eliminating contact line motion due to transient accelerations. Physical and chemical processes involving two-phase transport within these drops are more reproducible, and automated image analysis of the evolving drop contents is greatly simplified. This technique has particular promise for high-throughput protein solution screening in structural genomics and drug discovery.