A post-modified lanthanide metal-organic frameworks as ratiometric luminescent sensor for the visual detection of 5-hydroxytryptamine

5-Hydroxytryptamine (5-HT), a key neurotransmitter, is an important biomarker for carcinoid syndrome. We herein construct a ratiometric luminescent sensor by covalently coupling fluorescein 5-isothiocyanate (FITC) with lanthanide metal-organic frameworks (Ln-MOFs). In the presence of 5-HT, the emission of FITC increases while the emission of Eu^3 + decreases, accompanied by a distinct color change of emission from orange to green. This sensor not only has the advantages of high sensitivity (LOD = 0.04 μM), fast response (30 s), excellent selectivity, and large ΔE*_ab value (73), but can also be used for the detection of 5-HT in human serum and allow for instant visual detection with the assistant of smartphone. This ratiometric luminescent sensor offers an alternative avenue for early diagnosis of carcinoid syndrome.