Chitosan-Stabilized Self-Assembled Fluorescent Gold Nanoclusters for Cell Imaging and Biodistribution in Vivo

Biocompatible, near-infrared luminescent gold nanoclusters were synthesized in situ using as-prepared chitosan grafted with N-acetyl-l-cysteine (NAC-CS). The fluorescent gold nanoclusters coated with chitosan-N-acetyl-l-cysteine (AuNCs@NAC-CS) were aggregated by multiple ultrasmall gold nanoclusters closing with each other, with strong fluorescence emission at 680 nm upon excitation at 360 nm. AuNCs@NAC-CS did not display any appreciable cytotoxicity on cells even at a concentration of 1.0 mg mL^-1. AuNCs@NAC-CS were more insensitive to H₂O₂ and trypsin compared with fluorescent gold nanoclusters coated with Albumin Bovine V (AuNCs@BSA), which make them have long time imaging in HeLa cells. Furthermore, the obvious fluorescence signal of AuNCs@NAC-CS appeared in the liver and kidney of the normal mice after 6 h injection. And the fluorescence intensity decreased after that because of the highly efficient clearance characteristics of ultrasmall nanoparticles. These findings demonstrated that AuNCs@NAC-CS possessed good fluorescence, low cytotoxicity, and low sensitivity to some content of cells, allowing imaging of the living cells.