Exosomes are cell-derived nanovesicles that can carry nucleic acids, proteins, lipids, and other molecules from the cells of their origin. Exosomes isolation are found in almost all biological fluids, including blood, saliva, urine, semen, sputum, breast milk, and cerebrospinal fluid. Unlike tissue samples, they can be collected non-invasively over a long period of time, allowing continuous monitoring of disease progression and response to treatment. Compared with other circulating biomarkers, exosomes also have several advantages. They are abundant (thousands to billions per microliter of biological fluid), and their durability indicates that their internal integrity can be maintained through several freeze-thaw cycles. Differential centrifugation (including gradient ultracentrifugation) is a standard exosome separation technique.
