A turn-off fluorescence sensor of Eu-NDBC exhibits a rapid quenching to ascorbic acid, which can accurately monitor ascorbic acid 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 (H₂NDBC) with Eu³⁺ produced a europium MOF, Eu-NDBC. Eu-NDBC emits the combined emissions from the intraligand charge transfer (ILCT) of NDBC²⁻ ligand and ⁵D₀→⁷F_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 I₀/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=2.46×10³ M⁻¹ and K_q=4.96×10⁶ 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.