Polypeptide-Templated Au Nanoclusters with Red and Blue Fluorescence Emissions for Multimodal Imaging of Cell Nuclei

Noble metal nanoclusters (<2 nm) prepared using special molecules such as proteins and peptides as templates have been attracting increasing attention in biomedical applications and cell imaging because of their excellent biocompatibility, size-dependent fluorescence properties, and relatively simple synthesis. Although cell imaging using metal clusters has developed rapidly in recent years, multimodal imaging of the cell nucleus remains challenging. Herein, we report the successful synthesis of two different types of gold nanoclusters, one with blue fluorescence emission (λex 320 nm, λem 405 nm) and the other with red fluorescence emission (λex 560 nm, λem 657 nm), using the same polypeptide SV (sequence: NH2-CCYGGPKKKRKVG-COOH) as a template. The synthesis of these two optically distinct Au nanoclusters (Au NCs) was achieved through the optimization of synthesis conditions, including light, pH, the Au: polypeptide ratio, reaction time, and temperature. The multimodal imaging ability of the Au NCs were subsequently explored, with particular emphasis on the enzyme-like catalysis of the NCs and their use in the optical imaging of cell nuclei. Results show that the Au NCs possessed similar biological activities as the parent peptide used in their synthesis as well as demonstrating peroxidase-like activity due to the Au nanocluster core. Further, the Au NCs targeted the cell nucleus, with their strong fluorescence allowing cell imaging (cells containing Au clusters could be distinguished by eye, eliminating the need for additional labels). Finally, the Au NCs exhibited excellent multimodal cell imaging abilities. The results suggest that the Au NCs introduced here are promising candidates for the labeling and analysis of pathological samples.