Strongly emissive formamide-derived N-doped carbon dots embedded Eu (III)-based metal-organic frameworks as a ratiometric fluorescent probe for ultrasensitive and visual quantitative detection of Ag

In this study, a novel ratiometric fluorescent sensor for ultrasensitive and visual quantitative detection of Ag+ with naked eyes was rationally designed and synthesized by encapsulating formamide-derived N-doped carbon dots (FA-CDs) in the cavities of Eu(III)-based metal-organic frameworks (Eu-MOFs). Benefiting from the specific coordination interaction of C??N groups with Ag+, the firstly synthesized FA-CDs could selectively sense Ag+ based on the turn-off mode with a low detection limit (LOD) of 0.5 nM. After embedding FA-CDs in Eu-MOFs, owing to the robust self-calibration function and excellent accumulation effect of Eu-MOFs, the developed FACDs@Eu-MOFs-based ratiometric fluorescence (RF) probe has a more prominent selectivity toward Ag+ with an ultrasensitive fluorescence response across a broad range of 0.3?100 nM and an ultralow LOD of 80 pM, which is the lowest LOD value recorded of all the reported CDs-based and MOFs-based Ag+ sensors. The fabricated RF probe was successfully applied for the quantitative determination of Ag+ in environment water samples and commercial antibacterial Ag+ solution. More importantly, a novel FA-CDs@Eu-MOFs-based RF hydrogel sensor was successfully fabricated for the visual quantitative detection of Ag+ in commercial antibacterial Ag+ solution with naked eyes, which can be easily conducted without fluorophotometer-based calibration and provides an effective route to facilitate the evolution of visual fluorescent sensors from qualitative/semi-quantitative to quantitative detection.