Extracellular vesicles (EVs) have been identified as promising biomarkers for the noninvasive diagnosis of various diseases. However, challenges in separating EVs from soluble proteins have resulted in variable EV recovery rates and low purities. Researchers at Duke University have developed a high-yield ( > 90%) and rapid ( < 10 min) EV isolation method called FLocculation via Orbital Acoustic Trapping (FLOAT). The FLOAT approach utilizes an acoustofluidic droplet centrifuge to rotate and controllably heat liquid droplets. By adding a thermoresponsive polymer flocculant, nanoparticles as small as 20 nm can be rapidly and selectively concentrated at the center of the droplet. The researchers demonstrate the ability of FLOAT to separate urinary EVs from the highly abundant Tamm-Horsfall protein, addressing a significant obstacle in the development of EV-based liquid biopsies. Due to its high-yield nature, FLOAT reduces biofluid starting volume requirements by a factor of 100 (from 20 mL to 200 µL), demonstrating its promising potential in point-of-care diagnostics.
Mechanism of FLocculation via Orbital Acoustic Trapping (FLOAT)
method for the rapid isolation and efficient concentration of EVs
a Schematic depicting the heating and rotation process. Initially, small extracellular vesicles (sEVs) are randomly distributed throughout the droplet. When the acoustic transducers are turned on, the droplet rotates and heats. Once the droplet temperature rises above the lower critical solution temperature of PNIPAm (~32 °C), the flocculation process begins. As the droplet continues to rotate, particle flocs collide and merge, eventually forming a single particle floc at the center of the droplet. This floc can be manually transferred and resuspended in another buffer for subsequent analysis. (sEVs: small extracellular vesicles; T: droplet temperature; LCST: lower critical solution temperature). b Microscope images showing the concentration of the fluorescently labeled urinary sEVs inside a rotating liquid droplet. Scale bar: 200 µm. c Schematic depicting the various stages of the FLOAT process. d Sample to analysis pipeline for the concentration and isolation of urinary EVs