EVs from biofluids may be stored at -80 degree C for a period ranging from 7-14 days. It may not affect the protein content during this period of storage.
You may want to refer to the articles attached below.
Article Preservation of small extracellular vesicles for functional ...
Article Effect of storage on physical and functional properties of e...
Article Impact of Storage Conditions on EV Integrity/Surface Markers...
Article DNA in serum extracellular vesicles is stable under differen...