Improved enzyme immobilization for enhanced bioelectrocatalytic activity of choline sensor and acetylcholine sensor

In this work, we report the development of a highly sensitive and stable choline/acetylcholine sensor based on the synergetic effect of multi-walled carbon nanotubes and ZnO nanoparticles. This unique multi-layer structure provided a favorable microenvironment to maintain the bioactivity of choline oxidase and acetylcholinesterase, which led to a rapid amperometric response to choline and acetylcholine. This nanomaterials-based choline/acetylcholine sensor was highly sensitive and showed good stability over a relatively long-term storage (90 days). The sensor prepared by loading 1.0-unit choline oxidase and acetylcholinesterase showed a linear response range of 1.0 μM to 0.8 mM and 1.0 μM to 1.0 mM, a sensitivity of 178 μA mM−1 cm−2 and 180 μA mM−1 cm−2, and a detection limit of 0.3 μM, respectively. The sensor prepared was used to detect choline in human blood plasma samples, and the obtained results were consistent with those of the HPLC–MS/MS assay.