Precise acousto-electric sorting of submicron cell-secreted extracellular vesicles

Extracellular vesicles (EVs) are nano and submicron sized bioparticles produced by most of the cells in our body. They contain biological information such as ribonucleic acid and proteins which can be transferred to not only local cells, but also to remote cells since they circulate through most of the body fluids such as blood and urine. Two major subtypes of EVs - exosomes and microvesicles- carry different types of biomolecules from their parental cells due to their different biogenesis and secretion origin in the cell.

Due to their stability and composition, exosomes are invaluable markers and carriers for both disease diagnosis as well as delivering medicines across the body. However, their small size – measuring less than 200 nm, or one tenth of the size of a PM2.5 dust particle – makes it challenging to achieve a high throughput and efficient purification. Providing a precise and scalable sorting method for nano and submicron sized EVs could benefit diverse areas such as basic biological research, minimally invasive cancer diagnostics and exosome-based drug delivery.

An interdisciplinary research team led by Associate Professor Ye Ai from the Singapore University of Technology and Design (SUTD), in collaboration with Assistant Professor David Collins from the University of Melbourne, developed a novel hybrid acoustophoresis and dielectrophoresis (DEP) technology for an effective sorting and separation of submicron bioparticles and EVs.

The microfluidic sorting device used a tilted-angle surface acoustic wave transducer placed directly inside a microfluidic channel to simultaneously couple acoustic energy and electrical fields into the adjoining fluid domains. This was done to avoid the attenuation losses and generating multiple pressure node positions for laterally displacement of the particles. In this system, particles travelled towards the nodal positions between electrodes due to the acoustic radiation forces while the negative DEP force field synchronously directed them away from the electrodes where the pressure nodes were also located. The combination of acoustic/DEP forces not only decreased the critical diameter of the separated particles down to the exosome size range, but also made separation possible at lower pressure fields and powers compared to the application of these forces individually.

By taking advantage of this uniquely combined acoustic or DEP force field and tuning the electrical properties of the suspending solution, the team was able to demonstrate highly efficient separation of exosomes (<200 nm) and microvesicles (>300 nm) with over 95% purity and 81% recovery. This work represents a new and advantageous approach for submicron bioparticle manipulation, with potential applications in both biomedical research and clinical uses.

“The sorting of EV subtypes has gained increasing attention because of its extensive impact in various applications across the fields of biology, diagnostics and medicine. This work demonstrates new capabilities in the label-free precise sorting of submicron EVs, offering the ability to isolate intact, non-aggregated exosomes with a reproducible size range in diverse exosome-based applications,” explained principal investigator, Associate Professor Ai.

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This work was published in Nano Letters, a top-tier, multidisciplinary journal, covering a broad spectrum of topics in nano- and microscale experimental and theoretical studies. SUTD graduate students and postdoctoral fellows, including Mahnoush Tayebi and Dahou Yang participated in this research project. This study was supported by the Ministry of Education, Singapore, under its Academic Research Fund Tier 2 grant (MOE-T2EP30120-0017).