Background: Radionuclides have important roles in clinical tumor radiotherapy as they are used to kill tumor cells or as imaging agents for drug tracing. The application of radionuclides has been developing as an increasing number of nanomaterials are used to deliver radionuclides to tumor areas to kill tumor cells. However, promoting the efficient combination of radionuclides and nanocarriers (NCs), enhancing radionuclide loading efficiency, and avoiding environmental pollution caused by radionuclide overuse are important challenges that hinder their further development.
Methods: In the present study, a new small molecule compound (3-[[(2S)-2-hydroxy-3-(4-hydroxyphenyl)-1-carbonyl] amino]-alanine, abbreviation: HN, molecular formula: C₁₂H₁₆N₂O₅) was synthesized as a linker between radionuclide iodine-125 (¹²⁵I) and NCs to enable a more efficient binding between NCs and radionuclides.
Results: In vitro evidence indicated that the linker was able to bind ¹²⁵I with higher efficiency (labeling efficiency > 80%) than that of tyrosine, as well as various NCs, such as cellulose nanofibers, metal oxide NCs, and graphene oxide. Single-photon emission computed tomography/computed tomography imaging demonstrated the biological distribution of ¹²⁵I-labeled NCs in different organs/tissues after administration in mice.
Conclusion: These results showed an improvement in radionuclide labeling efficiency for nanocarriers and provided an approach for nanocarrier image tracing.

Keywords: nanocarriers, radionuclide labeling, radionuclide ¹²⁵i, SPECT/CT imaging