Traffic-light-type visual sensing of bilirubin: a dual-emission Au-Ag NCs/MOF-808/Tb nanocomposite based on an asynchronous quenching strategy.

A dual-emission nanocomposite (Au-Ag NCs/MOF-808/Tb) was designed based on an asynchronous dual-quenching strategy. Gold-silver nanoclusters (Au-Ag NCs) with red fluorescence were modified on the surface of lanthanide-functionalized MOF-808, constructing a sensing system with traffic-light-like color transitions. Unlike the conventional ratiometric probes that rely on a stable internal reference, this system features two BR-responsive channels with different quenching rate (BR, bilirubin). Specifically, the green emission of Tb3+ at 545 nm showed a faster and more sensitive response toward BR, whereas the red emission of Au-Ag NCs at 650 nm changed more gently. On this basis, the 545 nm channel was selected as the primary analytical signal to establish the quantitative calibration curve, which afforded a limit of detection for BR as low as 44.24 nM.The fluorescence intensity ratio I545/I650 was adopted to characterize the asynchronous response behavior of the dual-emission channels. Furthermore, by coupling the probe with a paper-based sensing platform and smartphone-assisted color analysis, visual and portable BR detection becomes possible with semi-quantitative concentration-range classification via a logic-gate scheme. By assembling multicomponent fluorescent materials with an asynchronous dual-response mechanism, this study demonstrates a new paradigm for the visual detection of biomarkers, and promotes the further development of portable analytical platforms.