Ratiometric fluorescence and chromaticity dual-readout assay for β-glucuronidase activity based on luminescent lanthanide metal-organic framework

Abstract

β-Glucuronidase (GCU) is a biomarker of many malignant tumors. The accurate and sensitive detection of GCU is of significance for the early diagnosis of diseases. Herein, we proposed a ratiometric fluorescence/chromaticity dual-readout assay method for GCU activity by integrating a luminescent lanthanide metal-organic framework (MOF) and fluorescence turn-on enzymolysis reaction. MOF-253 synthesized by Al3+ and 2,2′-bipyridine-5,5′-dicarboxylic acid was used as scaffold to prepare Eu3+@MOF-253 with red emission, which plays multiple roles in GCU assay including fluorescence internal standard, synergistic enzyme catalysis and chromaticity shift enhancement. 4-Methylumbelliferyl-β-glucuronide was selected as substrate and hydrolyzed by GCU to produce 4-methylumbelliferyl with blue emission, which can quench the fluorescence of Eu3+@MOF-253 due to internal filter effect. Therefore, the turn-on/off ratiometric fluorescence assay method of GCU was established, and it exhibits a wide linear range of 0.1–50 U L−1, low limit of detection (LOD) of 0.03 U L−1 and good selective response. Furthermore, a portable device with illuminometer as RGB signal readout was designed to perform the ratiometric chromaticity visual assay of GCU, which has the linear range of 0.2–40 U L−1 and the LOD of 0.06 U L−1. The dual-readout method was applied to detect GCU in human serum and shows high accuracy and precision (recovery of 92.4–114.1%, relative standard deviation < 7.9%). Both the ratiometric fluorescence and the ratiometric chromaticity assay get the same results as the classical colorimetric assay. To our knowledge, this is the first report on the ratiometric fluorescence/chromaticity dual-readout assay of GCU activity.