J Mol Biol. 2005 Feb 4;345(5):1015-26. doi:10.1016/j.jmb.2004.11.017

Bernath K, Magdassi S, Tawfik DS.

Directed evolution of protein inhibitors of DNA-nucleases by in vitro compartmentalization (IVC) and nano-droplet delivery.

Selection pressure can be increased by reducing the volume of the spheres.