Highly pH-Responsive Sensor Based on a Eu^III Metal–Organic Framework with Efficient Recognition of Arginine and Lysine in Living Cells

Abstract

A lanthanide-based three-dimensional metal-organic framework with excellent water, acid/base, and solvent stability, namely {[(CH₃)₂NH₂]_0.7[Eu₂(BTDBA)_1.5(lac)_0.7(H₂O)₂]·2H₂O·2DMF·2CH₃CN}<i>_n</i> (<b>JXUST-29</b>, H₄BTDBA = 4',4‴-(benzo[<i>c</i>][1,2,5]thiadiazole-4,7-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid), Hlac = lactic acid), has been synthesized and characterized. Since the N atoms of the thiadiazole group will not coordinate with lanthanide ions, <b>JXUST-29</b> has a free basic N-site accessible to small H⁺ ions, which allows it to be used as a promising pH fluorescence sensor. Interestingly, the luminescence signal was significantly enhanced, with an approximately 54-fold enhancement in the emission intensity when the pH value was increased from 2 to 5, which is the typical behavior of pH probes. In addition, <b>JXUST-29</b> can also be used as a luminescence sensor to detect l-arginine (Arg) and l-lysine (Lys) in an aqueous solution through fluorescence enhancement and the blue-shift effect. The detection limits were 0.023 and 0.077 μM, respectively. In addition, <b>JXUST-29</b>-based devices were designed and developed to facilitate detection. Importantly, <b>JXUST-29</b> is also capable of detecting and sensing Arg and Lys in living cells.