Acoustofluidic enzyme-linked immunosorbent assay (ELISA) platform enabled by coupled acoustic streaming

Bead-based ELISA in microfluidics is a promising platform for reducing the reagent consumption and improving assay throughput due to its fast binding kinetics and low reagent consumption. Current microfluidic bead-based immunoassay mainly relies on magnetic and centrifugal forces to manipulate microparticles to complete an assay protocol. Here we report an acoustic streaming-based microfluidic method that can perform all the fluid and particle operations of bead-based ELISA. A series of sharp-edge structures are used to generate a long-range coupled acoustic streaming that enables simultaneous particle trapping and active molecular exchange in a dead-end microchannel. The device achieved >99% of molecular exchange in 4 min, while maintaining a particle trapping efficiency of 85%. This acoustofluidic-based method demonstrates all three key operations in a bead-based immunoassay: (1) Beads "immobilization"; (2) Active mixing of fluid for bead/target binding; (3) Active molecular exchange for reagent loading and washing. Finally, on-chip quantitative detection of biomarker IL-6 with a limit of detection ∼50 pg/mL is achieved using this platform including an enzymatic signal amplification step. The small footprint, simple setup, and continuous flow operation of the acoustic streaming-based method makes it an attractive platform for continuous flow bead-based immunoassay.