Fabrication of avidin-stabilized gold nanoclusters with dual emissions and their application in biosensing.

Protein-stabilized gold nanoclusters (Prot-Au NCs) have been widely used in biosensing and cell imaging owing to their excellent optical properties and low biotoxicity. However, several Prot-Au NCs reported in the literature do not retain the biological role of the protein, which greatly limits their ability to directly detect biomarkers. This study demonstrated for the first time the successful synthesis of dual-function avidin-stabilized gold nanoclusters (Av-Au NCs) using a one-pot method. The resulting Av-Au NCs exhibited intense blue and red emissions under 374 nm excitation. Furthermore, the Av-Au NCs retained the native functionality of avidin to bind to biotin. When DNA strands modified with biotin at both ends (i.e., linker chains) were mixed with Av-Au NCs, large polymers were formed, indicating that Av-Au NCs could achieve fluorescence signal amplification by interacting with biotin. Taking advantage of the aforementioned properties, we constructed a novel enzyme-free fluorescent biosensor based on the Av-Au NCs-biotin system to detect DNA. The designed fluorescent biosensor could detect target DNA down to 0.043 nM, with a wide line range from 0.2 nM to 20 µM. Thus, these dual-functional Av-Au NCs were shown to be an excellent fluorescent material for biosensing.