A microfluidic droplet array demonstrating high-throughput screening in individual lipid-producing microalgae

Microalgae are a group of photoautotrophic microorganisms which could use carbon dioxide for autosynthesis. They have been envisioned as one of the most prospective feedstock for renewable oil. However, great endeavors will still be needed to increase their economic feasibility. The screening of competitive species and suitable culture conditions are such issues. To greatly accelerate these rather laborious steps and also improve their experimental lump-sum-manner, we developed a microfluidic droplet-based 2 × 10³ resolution "identification card", which allowed high throughput real-time monitoring of individual algae among population. A novel fluid-blocking-based droplet generating and trapping performance were integrated in the platform which made it excellent in operational simplicity, rapidity and stability and full of the potentials in single-cell-isolation/screening. The developed platform was successfully used to screen three unicellular algae, namely, Isochrysis zhanjiangensis, Platymonas subcordiformis and Platymonas helgolandica var. tsingtaoensis. In situ bioassays of the lipid accumulation and cell proliferation at single cell level for interspecies comparison were possible. Furthermore, lipid-producing inhomogeneity was demonstrated among cells in the same specie and batch. Nitrogen stress condition can be identified that induce positive-skewed frequency distribution of lipid content, even among individual inhomogeneous cells over the typically used culture condition.