Preparation of ATCh
S-acetylthiocholine iodide of 0.50 mmol was dissolved in 5 mL ultrapure water and then 0.60 mmol AgNO3 was added in the solution to remove I−, and the existence of I− in sensing system will increase detection limit. After removing AgI precipitate by centrifugation, NaCl of 0.20mmol was added into the solution and the formed precipitate was removed by further centrifugation. The concentration of resulting ATCh solution was regarded as 0.1 M and immediately used for the following experiments