Surface-Engineered Gold Nanoclusters with Biological Assembly-Amplified Emission for Multimode Imaging.

Here, we develop bifunctional ligand-engineered gold nanoclusters (AuNCs) as signal amplifying reporters for multimode imaging. Modified streptavidin (SA) and biotin alkyl acid-based ligands were applied to AuNCs to form AuNC-SA and AuNC-biotin. The zwitterionic ligands promoted bioassembly and avoided nonspecific adsorption. The AuNCs resisted aggregation-induced quenching and showed strong emission benefited from biological self-assembly. The engineered AuNCs featured stable emission, a large two-photon absorption cross section, long fluorescence lifetime, and good biocompatibility. Thus, cell-expressed antigen-induced protein-binding events were effectively converted into signals from the biological assemble of AuNCs. We performed a comprehensive assay of specific antigens and the cell structure, through one-photon imaging, two-photon imaging, and fluorescence lifetime imaging of AuNCs in a simple, sensitive, and reliable way.