Single-cell activity screening in microfluidic droplets

Water-in-oil emulsion droplets can be used as microcompartments to contain single cells that can be subjected to activity assays in this format. Microfluidic devices produce droplets at > kHz rates and can be coupled to modules to, e.g., add reagents, incubate or measure analyte concentration optically (with sensitivities as low as 2nM). The range of optical assays includes fluorescence and absorbance detection and examples for the use of these technologies for ultrahigh-throughput sorting in directed evolution and functional metagenomics are described.