What is the isolation principle of size-based exosome isolation techniques?

Size-based exosome isolation techniques rely on separating exosomes from other particles in a sample based on size alone. The two widely-used size-based exosome isolation techniques include: 

Size-Exclusion Chromatography (SEC)

SEC separates particles based on their size using a column filled with porous beads. When the sample is applied to the column, exosomes, which are smaller in size take longer to pass through the column while larger particles, such as proteins or cellular debris, elute from the column first. This allows for the separation and collection of exosomes in a purified fraction.

Ultrafiltration

The ultrafiltration technique uses porous membranes with specific pore sizes to separate particles based on their size. When the biological fluid is passed through the membrane under pressure, particles larger than the membrane's pore size are retained, while smaller particles, including exosomes, pass through. By using membranes with appropriate pore sizes, exosomes can be isolated from larger particles.