A Water‐Stable Europium Metal‐Organic Framework as a Turn‐Off Fluorescence Sensor for Ascorbic Acid Detection in Human Serum

Abstract Ascorbic acid (AA) is a biomarker of some nervous system diseases, whose detection is of significance in many fields. The hydrothermal reaction of naphthalene‐2,6‐dicarboxylic acid (H 2 NDBC) with Eu 3+ produced a europium MOF, Eu‐NDBC. Eu‐NDBC emits the combined emissions from the intraligand charge transfer (ILCT) of NDBC 2− ligand and 5 D 0 → 7 F j (j=1–4) transfers of Eu(III). The factors of MOF dosage, pH and fluorescence response time are optimized as 0.6 mg, 7.35, and 5 min respectively. The sensitivity test shows a linear fitting equation of I 0 /I=0.00239 ⋅ C AA +1.03774 (C AA =AA concentration), with its limit of detection calculated as 4.53 μM in a wide linear range of 0–900 μM. The linear fitting of Stern‐Volmer equation gives K SV =2.46×10 3 M −1 and K q =4.96×10 6 M −1 S −1 , suggesting Eu‐NDBC sensing AA is a dynamic fluorescence quenching process. Nine control amino acids can't affect Eu‐NDBC sensing AA and the emission intensity stay stable in five fluorescence quenching‐recovery cycles. The returned C AA closed to the set C AA and the recoveries around 100 % support the accurate AA detection by Eu‐NDBC in human serum. Totally, Eu‐NDBC can be regarded as a quantitative turn‐off fluorescence sensor to AA with high sensitivity and selectivity, rapid response and durability.