Combining sound and antibodies to isolate specific extracellular vesicles

Extracellular vesicles are tiny particles released by cells into biofluids like blood, carrying proteins and other molecules that reflect their cell of origin. Because different cells release different vesicles, isolating specific vesicle subpopulations could greatly improve biomarker discovery and disease monitoring. The challenge is doing this quickly, reproducibly, and with enough specificity for clinical use.

Researchers at Lund University in Sweden have developed a new approach that combines two complementary techniques to improve extracellular vesicle isolation. Acoustic trapping uses sound waves to gently capture vesicles from very small sample volumes with minimal preparation, making it fast and easy to automate. However, on its own, this method collects a broad mixture of vesicles and lacks molecular specificity.

To solve this, the team integrated acoustic trapping with immunoaffinity capture using antibody-coated beads. In their automated immuno-acoustic system, extracellular vesicles are first trapped acoustically from a tiny volume of blood plasma in just eight minutes. At the same time, vesicles expressing the surface marker CD9 bind specifically to antibody-coated silica beads, producing two vesicle fractions from a single run, a general vesicle population and a CD9-enriched subpopulation.

Schematic of acoustic trapping mechanisms taking place in this combined approach

The microfluidic capillary is vibrated with an ultrasound transducer at its resonant frequency, generating a localized acoustic field (illustrated with an orange glow). Traditional acoustic trapping is enabled by acoustically trapped microparticles (purple) which scatter sound (indicated in red) and experience radiation forces in the acoustic field, resulting in a cluster of these seed particles trapped in the pressure node. The resulting acoustic forces and hydrodynamic interactions enable EVs to be trapped between the seed particles, regardless of their surface marker expression. Immuno-acoustic trapping takes place at the same time as the acoustic trapping and is driven by the anti-CD9 binding (indicated in blue on the surface of the microparticles) to the antigens expressed on the CD9⁺ EVs.

The researchers carefully validated their approach using multiple analytical methods. Particle tracking and electron microscopy confirmed that intact vesicles were isolated, while proteomic analysis showed that the immuno-acoustic fraction was more strongly enriched for CD9-associated proteins than vesicles isolated by traditional immunoaffinity methods. Importantly, this automated workflow was far faster than standard manual protocols, which can take more than an hour and require repeated centrifugation steps.

This flexible platform can be adapted to target other surface markers, allowing researchers to isolate different extracellular vesicle subpopulations while retaining a broader vesicle background for comparison. Such capability could be valuable for biomarker studies, liquid biopsy applications, and research into disease-specific exosomes, where both specificity and speed are critical.