Novel and improved
biocatalysts are increasingly sourced
from libraries
via experimental screening. The success of such campaigns is crucially
dependent on the number of candidates tested. Water-in-oil emulsion
droplets can replace the classical test tube, to providein
vitrocompartments as an alternative screening format, containing
genotype and phenotype and enabling a readout of function. The scale-down
to micrometer droplet diameters and picoliter volumes brings about
a >107-fold volume reduction compared to 96-well-plate
screening. Droplets made in automated microfluidic devices can be
integrated into modular workflows to set up multistep screening protocols
involving various detection modes to sort >107variants
a day with kHz frequencies. The repertoire of assays available for
droplet screening covers all seven enzyme commission (EC) number classes,
setting the stage for widespread use of droplet microfluidics in everyday
biochemical experiments. We review the practicalities of adapting
droplet screening for enzyme discovery and for detailed kinetic characterization.
These new ways of working will not just accelerate discovery experiments
currently limited by screening capacity but profoundly change the
paradigms we can probe. By interfacing the results of ultrahigh-throughput
droplet screening with next-generation sequencing and deep learning,
strategies for directed evolution can be implemented, examined, and
evaluated.