Hierarchical hydrodynamic flow confinement: efficient use and retrieval of chemicals for microscale chemistry on surfaces.

We devised, implemented, and tested a new concept for efficient local surface chemistry that we call hierarchical hydrodynamic flow confinement (hierarchical HFC). This concept leverages the hydrodynamic shaping of multiple layers of liquid to address challenges inherent to microscale surface chemistry, such as minimal dilution, economical consumption of reagent, and fast liquid switching. We illustrate two modes of hierarchical HFC, nested and pinched, by locally denaturing and recovering a 26 bp DNA with as little as 2% dilution and by efficiently patterning an antibody on a surface, with a 5 μm resolution and a 100-fold decrease of reagent consumption compared to microcontact printing. In addition, valveless switching between nanoliter volumes of liquids was achieved within 20 ms. We believe hierarchical HFC will have broad utility for chemistry on surfaces at the microscale.