Metabolizable Small Gold Nanorods: Size-dependent Cytotoxicity, Cell Uptake and In Vivo Biodistribution.

Gold nanorods (AuNRs) with unique plasmonic properties in the near-infrared region have promising biomedical applications but suffer from poor in vivo clearance because of the large size. In this study, small AuNRs with a diameter of 7 nm (designated as sAuNRs) are found to have low toxicity and high clearance rates in vivo. Compared to common AuNRs with a diameter of 14 nm (designated as bAuNRs), sAuNRs exhibit similar surface plasmon resonance bands and photothermal efficiency as bAuNRs but have lower cytotoxicity as well as higher cell uptake. The in vivo biodistribution study indicates that only 0.68% of the intravenously injected sAuNRs remain in the body after 30 days, but the residual amount in the body after injection of bAuNRs is as high as 12.3%. The results demonstrate that the smaller AuNRs having lower toxicity and increased clearance in vivo have large clinical potential.