Methods for radiolabeling macromolecules

A method for detecting a disease or condition affecting blood circulation in a lung of a subject, the method comprising:

• administering intravenously to said subject a complex comprising a macromolecule that is selective for lung tissue and a carbon encapsulated nanoparticle composite having a radioactive particulate core, wherein the macromolecule is poly-lysine having a molecular weight of about 15 to 30 kilodaltons and wherein the carbon encapsulated nanoparticle composite is a carbon encapsulated 99mTc, 113mIn, 111In, 198Au, 64Cu, 213Bi, 57Co, 51Cr, 165Dy, 169Er, 59Fe, 153Gd, 166Ho, 177Lu, 103Pd, 81Rb, 82Rb, 186Re, 188Re, 75Se, 153Sm, 117mSn, 89Sr, 201Tl, 90Y, or 169Yb nanoparticle having a diameter of 10 to 500 nanometers;
• and
• detecting said complex in the lung of said subject, wherein the complex is produced in an aqueous medium comprising a pH selected to promote short-range attractive forces between the nanoparticle and the macromolecule by attenuating repulsive electrostatic forces, and wherein the complex accumulates in the lung and does not significantly accumulate in spleen or liver.