Amino-acid conjugated protein-Au nanoclusters with tuneable fluorescence properties

Au-based protein nanoclusters (PNCs) represent an emerging class of fluorescence probes that are inherently biocompatible and combine the functionality of proteins and optical properties of Au nanoclusters. Here we report on a methodology to create conjugated Au PNCs using amino acid coupling strategies from a series of common laboratory proteins. We discover that the host protein and the specific conjugation chemistry has a profound influence on the resulting fluorescence properties. Synchrotron analyses showcase local Au NC aggeration upon PNC conjugation, which causes local environment changes to invoke differences in fluorscence properties. The observed aggeration does not give rise to plasmonic properties nor signifigant fluorescence quenching, strongly indicating the PNCs are still in a near-native cluster state. Our methodology and findings here could open new pathways for tuning PNC fluorescence properties in a rational fashion, having a potential impact in host of biomedical and sensing applications.