Microfluidic platform for on-demand generation of spatially indexed combinatorial droplets.

We propose a highly versatile and programmable nanolitre droplet-based platform that accepts an unlimited number of sample plugs from a multi-well plate, performs digitization of these sample plugs into smaller daughter droplets and subsequent synchronization-free, robust injection of multiple reagents into the sample daughter droplets on-demand. This platform combines excellent control of valve-based microfluidics with the high-throughput capability of droplet microfluidics. We demonstrate the functioning of a proof-of-concept device which generates combinatorial mixture droplets from a linear array of sample plugs and four different reagents, using food dyes to mimic samples and reagents. Generation of a one dimensional array of the combinatorial mixture droplets on the device leads to automatic spatial indexing of these droplets, precluding the need to include a barcode in each droplet to identify its contents. We expect this platform to further expand the range of applications of droplet microfluidics to include applications requiring a high degree of multiplexing as well as high throughput analysis of multiple samples.