Use of Microfluidics for Directed Evolution of Biocatalysts and Materials in Droplets and Microgels

Microfluidics is used for droplet-based biochemical and biological assays in protein and metabolic engineering for designing novel biocatalysts. These systems are based on lab-on-chip and glass capillary devices that enable the encapsulation of organic and aqueous phase materials. Recently, together with lab-on-chip microfluidics, novel devices based on modular LEGO microfluidics have been developed that can be used to produce complex droplets and direct the evolution of proteins, cells, and materials in liquid droplets or microbeads. In vitro, compartmentalization of single genes or cells can be done in liquid microdroplets, microbeads, or microcapsules using microfluidic methods. Most often, substrates and detection systems based on absorbance, electrochemical measurements, fluorescence, mass spectrometry, and Raman spectroscopy can screen for more active protein variants. Efforts have also recently been made towards integrating microfluidics and flow cytometry, which are incompatible due to the use of different emulsion systems. Still, there are trials to achieve full automation and integration of these complex platforms. A novel approach emerges, where beads or capsules can be a substrate for compartmentalized enzymes, and cells, and this review will also tackle this most recent approach and the possibility of using it for the directed evolution and engineering of biocatalysts and (bio)materials.