Droplet formation from hydrodynamically coupled capillaries for parallel microfluidic contact spotting

The generation of liquid droplets at the exits of multiple capillaries coupled to a single flow source is evaluated for application to multiplexed microfluidic contact spotting. Using a simple analytic model and an iterative numerical model, relationships between applied flow rates and the number of channels which produce full droplets at their exits are determined for arbitrarily large arrays. Experimental validation is performed using eight-channel arrays fabricated in cyclic olefin copolymer chips, with good agreement between experimental and predicted data. Improvements in spotting repeatability and uniformity are achieved for microchannel arrays containing in situ porous methacrylate monoliths, particularly for individual channel flow rates below 1 μL min^-1, revealing contact spotting as an appropriate interface between multiplexed microfluidic liquid chromatography and off-chip analysis.