Scale-Down Platforms for Process-Oriented Enzyme Screening Using Microfluidics.

Enzyme screening platforms are typically evaluated based on their throughput and analytical performance rather than their ability to mimic the conditions encountered at large scale. In bioreactors, enzymes experience gradients in substrate concentration, oxygen availability, pH, temperature, and interfacial exposure, caused by imperfect mixing and multiphase operation. These gradients affect both enzyme activity and stability, yet they are rarely incorporated into the assays used to select biocatalysts. Traditionally, a variant is chosen based on its performance under static, well-mixed laboratory conditions, yet those conditions do not necessarily represent the process conditions it must eventually perform under. Microfluidic devices can in principle recreate process-relevant conditions at a small scale since these devices offer precise control over the flow, residence time, and multiphase contact. Yet most current platforms are not built to mimic the scale-down process-derived conditions. Here, we assess current microfluidic tools against this process-relevant conditions and outline how modular designs can be combined into sequential screening platforms that generate the conditions in a bioreactor, for early-stage biocatalyst selection.