AAVs are non-pathogenic versions of the adeno-associated virus that are re-packaged with genetic material to use for gene therapy. AAVs are proteinaceous capsids that are made up of 3 different proteins called viral protein 1, 2, and 3. The ratio of viral proteins defines the capsid serotype and the tissue that it will target. A typical AAV is about 25 nm and holds about 5 kb of single-stranded DNA. Some of the difficulties in characterizing AAVs include the size of the three- part viral protein complex and the variability of the payload composition (full, empty and/or partial).