Simultaneous Detection of MAO-B and Soluble Aβ Oligomers Based on a Bimetallic Loaded ZIF-8 Core–Shell Probe

The abnormal expression of monoamine oxidase B (MAO-B) and the soluble oligomer (Aβo) formed by β-amyloid deposition play key roles in the pathogenesis of Alzheimer's disease. However, the simultaneous detection of MAO-B and Aβo remains a huge challenge. Herein, a bimetallic core-shell probe ZIF-8 embedding rhodamine 6G (Au/Rh6G/Pd@ZIF-8) with peroxidase-like activity is designed to detect MAO-B and Aβo simultaneously. MAO-B catalyzes the substrate phenethylamine (PEA) to produce H₂O₂, which oxidizes thiamine with the catalysis of Au/Rh6G/Pd@ZIF-8 to produce a fluorescent product that emits a strong fluorescence at 440 nm. When Aβo is present in the system, due to the specific coordination between Aβo and Zn²⁺, the intact ZIF-8 structure collapses, leading to Rh6G release and fluorescence recovery. The simultaneous determination of MAO-B and Aβo by Au/Rh6G/Pd@ZIF-8 is realized. The results showed that the designed biosensor had high specificity and sensitivity, a wide detection range, and a low detection limit for MAO-B and Aβo simultaneous detection. Fluorescence signals for MAO-B and Aβo detection did not interfere with each other because they are excited separately, which provides more valuable data for the diagnosis of Alzheimer's disease.