Microfluidic method for rapidly determining the protein and lipid yield of microalgae

Microalgae are a promising source of green energy. They produce valuable bioproducts, such as proteins and lipids, and remove atmospheric carbon. In this study, we developed a microfluidic chip for culturing and screening for microalgae with high protein and lipid contents. Over 30 microalgae cultures can be grown in parallel in hanging drops on the chip and separately subjected to various experimental treatments, such as random mutations or different light levels. The microfluidic chip has a simple design and was fabricated from optically transparent polymethyl methacrylate; it could be easily operated without complex equipment (e.g., a syringe pump). The design was experimentally validated by culturing Cyanidium sp. and performing in-situ fluorescein measurements of its protein content after various ultraviolet and illumination treatments; significant increases in protein yield were observed for selected mutants (approximately 36 %) and further increased with optimized illumination (2500 lux; approximately 35 %). Moreover, Botryococcus braunii cultured in hanging drops that were separately immobilized using a biocompatible agarose gel for in-situ Raman spectroscopy measurements that rapidly determined the lipid composition. Our developed single-drop Raman spectroscopy method not only quantified the lipid content but also revealed its detailed chemical composition. In summary, the designed microfluidic chip is suitable for in-situ fluorescent assays and Raman microspectroscopy and is a compelling solution for high-throughput screening of algal lipids and proteins, reducing the labor required for breeding mutant algae and optimizing algal cultivation.