On-chip acoustic chaotic micromixer for point-of-care applications

Micro-mixing plays an important role in biochemical analyses using miniaturized total analysis systems (μTASs) or lab-on-chips. However, existing micromixers primarily rely on a specific medium and lack the capability of being activated on-demand, and it is rather challenging to ensure adequate analyte capture and fluid washing on the surface of each probe particle during the assay steps. Herein, we demonstrated a novel acoustic chaotic micromixer actuated by a Lamb wave resonator (LWR) array, which integrated all steps from the initial sample pretreatment, chaotic probe particle mixing, analyte trapping, and fluid washing to the ultimate signal acquisition, thereby fulfilling "sample-in-answer-out" medical needs. The high-speed microscale acoustic streaming vortices triggered by the four LWRs in the confined micro-channel can be utilized to accelerate the particles' velocity and enhance the collision between the probe particle and target analyte. In addition, the chaotic particle mixing effect was realized by on-demand controlling the direction and magnitude of the four-in-one drag force based on the programmable acoustic stimuli of each independent LWR. Besides, a compact cartridge was specifically designed to accommodate the acoustic chaotic micromixer and peripheral accessories (including an RF signal source, a CMOS optical sensor and a mini pump), thus presenting a handheld device for point-of-care applications. Finally, the trace amount of prostate specific antigen (PSA) derived from fingertip blood samples was effectively detected. Owing to the compact size, on-chip chaotic particle mixing, and fast and sensitive detection performance, the proposed acoustofluidic system is very suitable for on-site diagnostic applications.