Mass photometry is a single-particle analytical technology that measures the masses of biomolecules in their native states, in solution. The TwoMP and SamuxMP mass photometers are easy-to-use instruments that can measure masses of biomolecules between 30 kDa and 5 MDa, or AAV empty/partial/full ratios, requiring minimal sample and minimal sample prep for analysis. In this talk, we demonstrate the utility of the TwoMP as a tool to measure critical quality attributes of your samples, or to quickly, easily monitor antibody-antigen interactions, quantify small-molecule induced changes to complex formation, assess sample purity and more. We wil also discuss capabilities of the SamuxMP in characterizing AAV samples. We will show that it can differentiate between empty, partially filled and full AAV capsids, and that is serotype agnostic. The SamuxMP measurements are in line with gold-standard techniques such as TEM and AUC.