design and biodistribution of 99mtc-labeled gold/gold sulfide nanoconjugates: a preclinical evaluation in balb/c mice

Introduction: gold/gold sulfide (ggs) nanoparticles exhibit strong near-infrared (nir) absorption, high chemical stability, low cytotoxicity, and ease of surface functionalization, enabling deep tissue penetration and targeted cancer theranostics. this study aimed to develop and evaluate 99mtc-labeled pegylated ggs nanoconjugates for potential spect imaging applications.material and methods: ggs nanoparticles were synthesized by reacting haucl4 with na₂s and stabilized with polyvinylpyrrolidone (pvp). pegylated ggs nanoparticles were radiolabeled with 99mtc using sncl2, and radiochemical purity and stability were assessed via itlc in rpmi and human serum up to 24 h. cytotoxicity and cellular uptake were evaluated in ct26 colon carcinoma cells. biodistribution was studied in balb/c mice at 1, 4, and 24h post-intravenous injection by gamma counting of excised organs.results: 99mtc-ggs-pvp nanoconjugates had an average diameter of ~65.9 nm, maintained strong nir absorption post-labeling, and achieved high radiochemical purity (97.1 ± 1.1%) with stability >85% in rpmi and >82% in human serum at 24h. cytotoxicity was minimal, with 78% cell viability at 125 ggs. cellular uptake increased from 1.98% at 2h to 10.0% at 24h. in vivo, the liver showed the highest uptake (51.44 ± 7.54 %id/g at 1h), decreasing to 14.19 ± 6.54 %id/g at 24h; spleen uptake was markedly lower (1.51 ± 0.81 %id/g at 1h, 0.765 ± 0.28 %id/g at 24h).conclusion: the synthesized 99mtc-ggs-pvp nanoparticles demonstrated high stability, low toxicity, favorable biodistribution, and preserved nir absorption properties, making them promising candidates for dual-modality cancer theranostics. their radiolabeling efficiency and biodistribution support their use as radiotracers for spect imaging and potential integration into combined diagnostic and therapeutic (theranostic) platforms.