Carbon dots@zeolitic imidazolate framework nanoprobe for direct and sensitive butyrylcholinesterase assay with non-enzymatic reaction

Butyrylcholinesterase (BChE) was clinically considered an important biomarker for the diagnosis of liver diseases. Ellman's strategy (enzyme-catalyzed reaction) is normally utilized as a standard protocol for BChE activity sensing due to the different properties of substrate choline (Ch) and product thiocholine (TCh). However, there remain respective drawbacks besides the laborious operation procedure and time-consuming. We herein report the first example of using nanoscale zeolitic imidazolate framework (ZIF-8), self-assembled from 2-Methylimidazole (2-MIm) and Zn2+, to directly and target detect BChE. Encapsulation of fluorescent carbon dots (CDs) into ZIF-8 suppresses the emission of CDs, while the competitive coordination between BChE and the metal node of ZIF-8 can result in the release of CDs for BChE sensing. The sensing mechanism was studied in depth via experimental investigations, and multifarious luminescent guests, metal nodes, and organic ligands were employed to confirm that the rupture of ZIF-8 was due to the connection of BChE and Zn2+ caused by electrostatic attraction. The limit of detection (LOD) as low as 1.5 U L−1 was achieved with this sensing platform. Finally, this platform was applied to quantify BChE in 40 clinical serum samples of patients with clinical liver disease and showed great consistency with clinical diagnostic results.