Deep-Red Fluorescent Gold Nanoclusters for Nucleoli Staining: Real-Time Monitoring of the Nucleolar Dynamics in Reverse Transformation of Malignant Cells.

Nucleoli are important subnuclear structures inside cells. We report novel fluorescent gold nanoclusters (K-AuNCs) that are able to stain the nucleoli selectively and make it possible to explore the nucleolar morphology with fluorescence imaging technique. This novel probe is prepared through an easy synthesis method by employing a tripeptide (Lys-Cys-Lys) as the surface ligand. The properties, including deep-red fluorescence emission (680 nm), large Stocks shift, broad excitation band, low cytotoxicity, and good photostability, endow this probe with potential for bioanalytical applications. Because of their small size and their positively charged surface, K-AuNCs are able to accumulate efficiently at the nucleolar regions and provide precise morphological information. K-AuNCs are also used to monitor the nucleolar dynamics along the reverse-transformation process of malignant cells, induced by the agonist of protein A, 8-chloro-cyclic adenosine monophosphate. This gives a novel approach for investigating the working mechanism of antitumor drugs.