Size-Dependent Effect of Indocyanine Green Nanoimaging Agent for Metastatic Lymph Node Detection

Identification of metastatic lymph nodes is a crucial step in lymph node dissection to prevent further cancer spread and recurrence. However, the current limitations in metastatic lymph node detection often result in extensive resection of normal lymph nodes, leading to serious complications. The clinical application of indocyanine green (ICG) as a tool for lymph node detection is challenging because of its short plasma half-life and rapid light-induced decomposition and clearance. To overcome this limitation, we used polydopamine nanoparticles (PNs) as carriers for ICG and screened for the optimal particle size for detecting metastatic lymph nodes. ICG/PNs with sizes of 80, 160, 300, and 600 nm were synthesized, and their ICG loading efficiency, physical stability, and lymph node distribution were evaluated. The ICG absorbed on the PNs was found to be protected from light degradation, and its retention at the lymph nodes was improved. Notably, the ICG/PNs favored the fluorescence signal at the metastatic lymph nodes compared to the nonmetastatic lymph nodes. Among the tested particle sizes, the 80-nm ICG/PN showed a higher distribution in the metastatic lymph nodes. This study suggests that the 80-nm ICG/PN is a potentially valuable reagent for the detection and diagnosis of lymph node metastasis.