For which applications is it important to quantitate exosome number?

For most applications, assessing the relative amount of exosomal protein present (via Western blot or other protein quantification method) is a sufficient indication of the proportion of exosomes present. However, some applications require information about the absolute number of exosomes present in a solution, such as the use of exosomes to deliver therapeutic agents. Quantitation will be an essential step to standardizing the number and size of exosomes selected as cargo delivery particles.