A Stable Eu III Metal–Organic Framework Sensor for the Fluorescence Detection of Tryptophan and Cancer Biomarker in Living Cells

Amino acids and cancer biomarkers are crucial for human health and tumor monitoring. The establishment of rapid, accurate, sensitive, and simple detection methods is of great significance for disease prevention, early diagnosis, and therapeutic effect monitoring. Herein, a new three-dimensional metal–organic framework with the formula {[Eu 4 (BTDBA) 3 (DEF) 4 (H 2 O) 2 ]·1.25DEF·2H 2 O} n ( JXUST-55, where JXUST denotes Jiangxi University of Science and Technology, H 4 BTDBA = 4′,4‴-(benzo[ c ][1,2,5]thiadiazole-4,7-diyl)bis([1,1′-biphenyl]-3,5-dicarboxylic acid; DEF = N, N -diethylformamide) was successfully synthesized. After JXUST-55 was soaked in the aqueous solutions with different pH values (3–13) and organic solvents for at least 24 h, the structure remained stable, demonstrating high pH and chemical stability. As a potential fluorescent sensor, JXUST-55 selectively recognizes tryptophan (Trp) and 5-hydroxyindole-3-acetic acid (5-HIAA) via significant fluorescence quenching in aqueous solution, with limits of detection of 0.45 and 0.42 μM, respectively. Portable composite films based on JXUST-55 enable the naked-eye visual detection of targets. Furthermore, by utilizing the selective fluorescence quenching property of 5-HIAA in the aqueous solution, JXUST-55 reveals the core code “2026” in the “8888” pattern and performs well in latent fingerprint recognition. Importantly, JXUST-55 represents an ideal candidate for fluorescent sensing of Trp and 5-HIAA in living cells.