Iodine-Labeled Au Nanorods with High Radiochemical Stability for Imaging-Guided Radiotherapy and Photothermal Therapy

Radioactive iodine labeled gold nanomaterials (Au NMs) have been widely used in biomedical application such as cell tracking and disease theranostics. The radiolabeling can be accomplished via simply mixing Na131I and Au NMs ([131I(−1)] Au NRs) due to the specific absorption between iodide ions and Au NMs. However, it is reported that the absorption strength is highly dependent on the incubation medium and the serious detachment of 131I from [131I(−1)] Au NRs-PEG in vivo inhibited their application. We found that adding a simple preoxidization treatment of Na131I could greatly improve their radiochemical stability both in vitro and in vivo. The [131I(0)] Au NRs-PEG we prepared barely showed iodine detachment in different media and demonstrated 6 times higher cellular internalization of radioactivity than that of [131I(−1)] Au NRs-PEG since the detached radioiodine of which could not enter the cells. The mechanism study pointed out that the preoxidized iodide could chemically react with Au NRs, mediating Au etching. But with trace amount of 131I, both the morphology and the optical property of Au NRs can be well-maintained. Our [131I(0)] Au NRs-PEG was successfully retained in the tumor over 24 h after intratumoral injection and demonstrated synergistic radiotherapeutic and photothermal therapeutic effects. We believed that this simple and rigid labeling process improvement could promote the biomedical application and clinical translation of radioactive iodine labeled Au NRs.