Radiolabelling

Radiolabelling is the process of attaching a radioactive isotope to a biologically active molecule, such as a peptide, antibody, nucleic acid, carbohydrate, or small molecule, to enable imaging, tracking, or therapy. The label allows the distribution, pharmacokinetics, and biological fate of the labelled compound to be studied in living systems or for delivering radiation to a target site.

Labeling can be performed directly, by incorporating a radionuclide into the molecule, or indirectly, by attaching a radionuclide through a chelator, prosthetic group, or reactive handle. Indirect methods often use chelators such as DOTA, NOTA, or DTPA to coordinate radiometals (for example technetium-99m, gallium-68, lutetium-177) or radiohalides for iodine. Direct labeling can involve halogenation (e.g., iodine-125 or iodine-131) or other isotope incorporation strategies. Labeling conditions—pH, temperature, redox state, and reaction time—are critical for stability and activity, and the resulting product must be stable in biological conditions.

Quality control is essential and typically includes radiochemical purity, sterility, apyrogenicity, pyrogen testing, and assessment of specific activity. In clinical settings, radiopharmaceuticals must meet regulatory standards and undergo reproducible manufacture in radiopharmacy facilities.

Production sources include generators (e.g., Mo-99/Tc-99m), cyclotrons (for isotopes such as fluorine-18 and gallium-68), and nuclear reactors for others. Safety considerations cover radiation dose, handling, and shielding.

Applications span diagnostic imaging, using SPECT or PET to visualize processes in vivo, and targeted radiotherapy, delivering cytotoxic radiation to diseased tissue. Radiolabelling remains a central technique in nuclear medicine and biomedical research.