Dual-ModeSensing Platform Based on Eu/Ag–CaMOF for Cysteine Detection: Synergistic Enhancement of Fluorescenceand Catalytic Activity by Ag+

Cysteine (Cys), an important sulfur-containing biomarker, is closely associated with various diseases, yet achieving selective recognition and multifunctional signal output within a single platform remains challenging. Herein, a site-selective coordination strategy is employed to construct a synergistic Eu/Ag-Ca metal-organic framework (MOF) by incorporating Eu3+ and Ag+ into a Ca-based framework. Ag+ enhances Eu3+ luminescence by modulating energy transfer, while simultaneously serving as catalytic active sites to impart oxidase-like activity and as specific recognition sites for Cys via strong thiol affinity. Based on these synergistic effects, a dual-mode fluorescence/colorimetric sensing platform is developed, enabling rapid, selective, and sensitive detection of Cys with cross-validated signals. Furthermore, integration into a hydrogel matrix combined with RGB analysis and logic gate design allows visual and quantitative evaluation of abnormal Cys levels. This work provides a rational strategy for constructing multifunctional MOF-based sensing systems.