Sensitive fluorescence detection of baicalin in biological samples using Eu3+-based metal–organic frameworks

Baicalin, a major flavonoid compound found in Scutellariae radix, is the first SARS-CoV-2 3CLpro virus inhibitor. Therefore, developing an accurate and reliable strategy to detect baicalin in biological systems is vital. Herein, we report the first indolyl-lanthanide metal–organic framework (MOF) materials and their application as baicalin sensors. The results of this study indicate that the new crystal structure has good stability and luminous performance. The detection limits of baicalin in serum and urine are 0.05 and 0.04 μmol/L, respectively, suggesting high sensitivity and selectivity. Various background substances present in practical samples, such as anions, cations, and amino acids, do not interfere with the photoluminescence analytical signal of Eu³⁺. We identified that the quenching of the Eu-MOF is due to the inner filter effect, absorption energy competition, and photoinduced electron transfer among the baicalin, ligand, and MOF through powder X-ray diffraction analysis, Fourier transform infrared spectroscopy, luminescence lifetimes, ultraviolet studies, and computational analysis. Thus, we designed a convenient, sensitive, and facile detection method using the Eu-MOF and demonstrate that Eu³⁺-based materials are promising sensors for baicalin detection in actual serum and urine. Additionally, the prepared Eu-MOF@polyvinyl alcohol composite matrix membrane test film has considerable practical application value for the portable detection of baicalin.