Energy transfer from luminescent gold nanoclusters to non-luminescent silver nanoparticles from a new perspective

Histidine protected luminescent gold nanoclusters (Au@His NCs) were synthesized that interact with non-luminescent silver nanoparticles (Ag NPs) through a resonance energy transfer (RET) process where the latter acts as dark quencher. The interaction is collisional in nature as deduced by applying the Stern-Volmer equation. On external addition of a model transport protein (human serum albumin, HSA), the surface of the Au@His NCs accepts the proteins through physisorption that results into considerable enhancement of the luminescence of the Au@His NCs. The protein adsorbed Au@His NCs, on the other hand, possibly cling to the surface of the larger Ag NPs. This is confirmed from the quenching pattern of the emission from the Au@His NCs and time-resolved spectroscopy. The process contravenes the efficiency of RET and reduces the transfer of energy from the more luminescent Au@His NCs to the non-luminescent Ag NPs. On interaction with Ag NPs, the emission maximum shifts considerably to higher wavelength suggesting stabilization (due to restricted translational and rotational motions) of the Au@His NCs. The results are intriguing since the protein-aided adsorption of the luminescent Au@His NCs could restrict the energy transfer to the adsorbent (Ag NPs) in a quantitative way.