Fig. 6. Screening techniques. Some of the most frequent screening techniques are depicted. (a) Variants of proteins that confer fluorescence can be screened by analysing with digital imaging techniques cultures in solid media. (b) For proteins whose activity can be linked to a colorimetric assay or to the generation of fluorescence, it is possible to automatically transfer individual colonies to liquid cultures by means of automated multi-well liquid culture devices. The liquid cultures or their lysates can then be screened by colorimetric or fluorescent-based assays. (c) FACS enables the physical separation of individual cells based on their fluorescence properties, allowing for a higher throughput and reduced material and physical requirements. However, it is limited to biomolecules whose activity can be linked to a change in fluorescence. (d) IVC techniques replace the compartmentalization provided by cells with artificial compartmentalization, most frequently provided by emulsions of water and oil. This allows to bypass the limitation imposed by transformation efficiency, but incompatibilities between the conditions required for transcription and translation and those required for the activity of the biomolecule of interest reduce its scope of application. IVC: in vitro compartmentalization; w–o: water-in-oil; w-o-w: water-in-oil-in-water.