Acetylcholine Detection Based on pH-Sensitive Liposomes

[Image: see text] The pH-sensitive liposomes were employed to amplify the detection of acetylcholine (ACh). Acetylcholinesterase (AChE) covalently immobilized on the magnetic particles and the pH-sensitive liposomes encapsulating ferricyanide were added to a cyclic voltammetry cell solution where ACh was distributed. The conversion of ACh into acetic acid seemed to induce the pH decrease that caused the reduction in the electrostatic repulsion between the head groups of weakly acidic 1,2-dipalmitoyl-sn-glycero-3-succinate. The reduction generated liposome destabilization, which released potassium ferricyanide encapsulated inside the liposomes. The effects of the ACh concentration and pH were investigated. An addition of 10 μL of more than 0.5 mg/mL ACh concentration into 5 mL of a cyclic voltammetry cell solution was necessary to observe the response. The activity of AChE was reversible with respect to the pH change between 7 and 5. The sensitivity of this detection was almost identical to comparable techniques such as enzyme-linked immunosorbent assay, field-effect transistor, fluorescence, UV spectrometry, magnetic resonance imaging, and surface plasmon resonance. Therefore, the methodology developed in this study is feasible as a portable, rapid, and sensitive method.