Confinement of gold nanoclusters on hydroxy double salt for versatile fluorescent sensing of bio-enzymes

Fluorescent gold nanoclusters (AuNCs) have generated significant research interest because of their fascinating physicochemical properties. However, their biosensing applications are limited by the relatively low quantum yield (QY). Herein, a simple confinement effect based on AuNCs as guest molecules and Zn-containing hydroxy double salt (HDS) as host material (AuNCs@HDS) was used to significantly improve the fluorescence properties of AuNCs. The QY increased from 1.24% to 22.80%, and the time-tedious preparation or purification procedures were avoided. Further, the validated excellent fluorescence properties of AuNCs enabled the construction of a versatile fluorescent sensing strategy for bio-enzymes for the first time. The p-nitrophenol (pNP), a product of many bio-enzymes-catalyzed hydrolyses of pNP-substrate, can effectively quench the fluorescence of AuNCs@HDS through an inner filter effect (IFE) process. Therefore, the AuNCs@HDS successfully detected several enzymatic disease biomarkers with robust analysis capabilities by varying the pNP-substrate, including alkaline phosphatase (ALP), β-glucosidase (β-GLU) and β-galactosidase (β-GAL). This study will inspire the design of highly fluorescent AuNCs as tools for biosensing.