ABSTRACT - 591047 The disclosure relates to method of radiolabelling a biological entity comprising the step of contacting a suspension of the biological entity with an iodinated (125I) construct of the structure F-S-L for a time and at a temperature sufficient to allow localisation of the 125I to the surface of the biological entity where F comprises an iodinated histidine (His) residue or an iodinated tyrosine (Tyr) residue, S is a spacer covalently linking F to L, and L is a lipid, wherein the biological entity is a cell or an enveloped virus.
