Quantitative Detection of Acetylcholine in Mouse Brain Tissues Using Zeolitic Imidazolate Frameworks/ Graphitic Carbon Nitride Quantum Dots/ Acetylcholinesterase Complex

Using zinc acetate dihydrate, 2-methylimidazole, graphitic carbon nitride quantum dots (g-CNQDs, 7 mg) and acetylcholinesterase (AchE) as starting materials, the acidity sensitive complex of zeolitic imidazolate frameworks (ZIFs) containing g-CNQDs and AchE (denoted as ZIFs@g-CNQDs@AchE) was prepared by one pot method. In order to determine Ach, the complex and brain tissues samples of mouse with AD were reacted in the pH 7.4 phosphate buffer solution at room temperature for 2.5 h, and the fluorescence intensity of the system was measured at 475 nm with excitation wavelength of 380 nm. It was shown that the synthesized complex had a dodecahedron structure with an average particle size about 300 nm. After adding Ach, Ach penetrated into the complex and was catalyzed by AchE to generate acetic acid. The acidity of the system increased, the complex structure was collapsed, g-CNQDs were released, and an obvious fluorescence emission peak appeared at 475 nm. The linear relationship between values of the concentration of Ach and the corresponding fluorescence intensity of the system was kept in the range of 5.5-82.5 mmol·L^-1, with detection limit (3S/N) of 1.83 mmol·L^-1. Common interfering substances (glucose and dopamine) and interfering ions (Fe²⁺, Fe³⁺, Cu²⁺, Mg²⁺ and Zn²⁺) did not interfere with the detection of Ach, indicating that the specificity of the complex was high. Test for recovery was made according to standard addition method on the positive actual samples, and Ach was successfully detected, giving recoveries in the range of 93.2%-112% and RSD (n=5) of the determined values in the range of 0.82%-3.4%. The constructed acidity sensitive complex can serve as a potential carrier for the diagnosis and treatment of AD.