Rational design and detection applications of ratio fluorescence sensing based on CDs@Ln-MOFs composites

Luminescent metal-organic frameworks (LMOFs) demonstrate immense potential in sensing applications due to their tunable crystal structures, ordered porosity, and abundant functional sites. However, conventional LMOF sensors based on single emission centers remain susceptible to environmental interference, limiting their detection reliability in complex media. To overcome this limitation, research has shifted toward ratio-based fluorescence sensing platforms with built-in self-calibration capabilities. Among these, synergistically integrating carbon dots (CDs) with lanthanide ions (Ln³⁺) within MOFs to create CDs@Ln-MOFs composites represent one of the most promising strategies. This composite ingeniously combines the confinement and enrichment effects of MOFs, the sharp emission lines of Ln³⁺ (serving as a stable internal standard), and the broad-spectrum emission and response characteristics of CDs. Through dual-signal output and self-compensation mechanisms, it achieves significantly enhanced sensing performance. This review systematically evaluates the rational design, preparation methods, luminescence mechanisms, and sensing applications of CDs@Ln-MOFs composites. It first outlines the synthesis and luminescent properties of carbon dots, followed by detailed explanations of CDs@Ln-MOFs construction strategies (such as in situ synthesis and post-synthesis modification) and their fluorescence sensing mechanisms (including quenching, enhancement, and ratio-based sensing). Subsequently, it highlights application advancements in detecting ions, biomolecules, disease biomarkers, and antibiotic drugs. Finally, it outlines future directions in early diagnosis and environmental monitoring, aiming to provide theoretical guidance for designing next-generation high-performance fluorescent sensing platforms.