Silk fibroin protein-templated gold nanoclusters for in vivo fluorescence imaging.

Protein-templated synthesis has been proved to be an effective approach for building high-performance fluorescent bioimaging agents. Nevertheless, the high cost of proteins has restricted its wide application. Silk fibroin is a low cost natural protein with superior properties, which holds significant application prospects in many biomedical fields. However, its application potential in the biomedical imaging field remains to be explored. Herein, we report a one-pot green synthesis of high performance gold nanoclusters (AuNCs) using silk fibroin as stabilizer. The SF-AuNCs (~ 1.8 nm) shows a red emission around 600 nm with a large Stokes shift of 200 nm and a quantum yield of 5.42% which is comparable with that of fluorescence proteins. Meanwhile, the lifetime is as high as 3.47 μs which is about three magnitude orders higher than that of most molecular dyes and fluorescence proteins. Moreover, the stability is also greatly enhanced than that of the classical GSH-AuNCs. The SF-AuNCs is also well performed in cell labeling and in vivo imaging in zebrafish. This work not only provides a promising high performance protein fluorescence nano agent for bioimaging, but also expands the potential of the silk fibroin application in the biomedical imaging field.