Sac including a detectable metal marker and use thereof in an assay

摘要

A sac, in particular a vesicle, having a detectable metal, in particular a rear earth metal, encapsulated therein. The sac may be sensitized with a ligand and used in an assay. The vesicle is stored and/or used in an aqueous solution which includes the rare earth metal to increase the concentration of metal in the sac.