Targeted surface-functionalized gold nanoclusters for mitochondrial imaging.

Due to mitochondria involved in both apoptotic and necrotic cell death, labeling and imaging mitochondria has attracted considerable interest. However, conventional organic dyes used for mitochondrial imaging are limited because of their poor photostability. Considering that gold nanoclusters (AuNCs) possess some advantages over considerable interest, such as excellent photostability and strong fluorescence emission, we herein prepared a mitochondria-targeted fluorescent probe, AuNCs@CS-TPP, based on a covalent link between triphenylphosphonium (TPP) cations and chitosan-coated AuNCs (AuNCs@CS). The as-prepared AuNCs@CS-TPP exhibited a bluish fluorescence emission at 440 nm with a quantum yield of 8.5%. Meanwhile, the fluorescence intensity of AuNCs@CS-TPP labeled HeLa cells did not show apparent decrease after 8 min irradiation. Cytotoxicity assay showed that AuNCs@CS-TPP did not display any appreciable cytotoxicity on cells even at a concentration of 60 μg mL(-1). In addition, the result of fluorescence co-localization imaging in vitro indicated that AuNCs@CS-TPP could selectively accumulate into mitochondria of HeLa cells and HepG2 cells. These findings demonstrated that AuNCs@CS-TPP possessed superior photostability, low cytotoxicity, high sensitivity and target-specificity to mitochondria, allowing labeling and imaging of the mitochondria in living cells.