Why don’t I see a pellet after centrifuging my exosomes?

Unless your starting material (cell culture medium, serum, plasma, urine, etc.) was a large sample or particularly enriched for exosomes, you should not expect to see your pellet after centrifugation. Exosome pellets are small, glassy are nearly impossible to see in an ultracentrifuge tube. Rest assured, if you follow the isolation protocol, your exosomes are present in the tube.