Label-free droplet-based bacterial growth phenotype screening by a mini integrated microfluidic platform

Rapid and accurate microbial screening, which is important in industrial breeding, enzyme directed evolution and synthetic biology, is currently time-consulting. Fluorescence-activated droplet sorting (FADS) system offers a promising alternative for microbial screening with high-throughput analysis. However, pre-labeling steps are required before use. Here, a low-cost, label-free droplet-based mini integrated microfluidic platform is developed for bacterial growth phenotype screening based on the difference in droplet autofluorescence properties. The platform integrates the main functions into a box, in which droplets are passed through the detection area and transmitted the signal of the light directly to the photomultiplier tubes (PMT) through the optical fiber inserted in a specially designed chip. After optimizing the chip structure and parameter, we firstly verify the capabilities of this platform for bacteria automatic counting. Then, label-free counting and sorting of the cultured bacteria in droplet have been well performed in this platform with the support of a voltage amplifier. We also employee this platform to determine the growth phenotype for microbial strain in droplets and screen the fast-growth bacteria in an automatic way. The label-free droplet-based platform provides an automated method for rapid bacteria growth phenotype screening, which can be further employed in high quality industrial strains screening, anti-biotic resistance and directed evolution.