Microalgae concentration system for early harmful algae bloom detection using inertial microfluidic focusing

Early detection of harmful algal blooms remains challenging due to the low abundance of target microalgae and the limited sensitivity of conventional detection methods. Here, we present a high-throughput microfluidic cell concentrator that enables rapid and efficient pre-concentration of microalgae from large sample volumes. The system integrates a multiplexed inertial microfluidic device with a recirculation system, allowing repeated concentration cycles without manual sample transfer. Using the concentration system, we demonstrated the concentration of suspensions of a normal microalga (C. vulgaris) and a harmful cyanobacterium (M. aeruginosa). Starting from an initial density of 1 × 10⁵ cells/mL and a volume of 1 L, three concentration cycles increased the cell density to the 10⁷ cells/mL range within 90 min. The increased cell density resulted in more than a 100-fold enhancement in fluorescence signal measured using a plate reader. Excitation-emission matrix analysis further demonstrated that pre-concentration significantly improved species-specific fluorescence signatures. These results indicate that the proposed microfluidic concentrator enables rapid, scalable, and effective enrichment of microalgae and offers a promising platform for early detection and monitoring of harmful algal blooms.