Adeno-associated viruses (AAVs) are often used as vehicles for gene therapy. During the production process, many empty or partially filled capsids may be produced, which do not provide any benefits in the therapeutic process, but can impact immunogenicity and efficacy. The full/empty/partially full ratio of capsid is one of the most important Critical Quality Attributes (CQAs)of gene delivery vehicles to characterize. Analytical ultracentrifugation sedimentation velocity (AUC-SV) can measure the ratio of full and empty capsids by separation based on mass and buoyancy of full and empty particles. Cryo-TEM on the other hand can directly visualize capsids with various payloads. In addition, cryo-TEM allows you to also determine additional critical quality attributes such as particle size distribution, particle titer, and more. Another significant consideration is that cryo-TEM requires only 3μl of sample per experiment, whereas AUC-SV can require up to 400μl of sample.