Archimedes is an innovative, high-performance system which harnesses the technique of resonant mass measurement in order to detect and count particles in the size range 50nm - 5µm and to measure particle mass and size. Archimedes is uniquely positioned to quantitatively measure protein aggregates within and beyond the range of 200nm - 5µm, highlighted as a particular concern for immunogenicity and product safety. Central to Archimedes is a MEMS (Micro Electro-Mechanical Systems) technology sensor, allowing the highly sensitive, reliable and reproducible measurement of aggregates, one by one. Archimedes is also capable of providing information on sample concentration, viscosity, polydispersity, density and volume, and distinguishing between negatively buoyant proteinaceous particles and positively buoyant contaminating silicone oil droplets.