Optimizing the properties of biological molecules is crucial for numerous industrial and medical applications. Directed evolution, a potent technique for modifying biomolecules like proteins or nucleic acids, mimics natural evolution to enhance desired properties through selective pressure and sorting improved variants. Droplet-based microfluidic systems provide a high-throughput solution, overcoming screening limitations and enabling the analysis of variants in complex libraries. We optimize different biomolecules such as enzymes, fluorescence proteins, or epitopes using droplet-based microfluidics, emphasizing in molecular processes, the integration of microfluidics, and comparing advantages and limitations with low-throughput methods.