Non-enzymatic sensor based on doped polyindole/multi-walled carbon nanotube for detecting neurotransmitter acetylcholine

Abstract

A facile non-enzymatic acetylcholine sensor composed of doped-polyindole/multi-walled carbon nanotube (dPIn-MWCNT) composite was designed, fabricated, and presented here. The negative current response toward acetylcholine concentration was first found and reported here. The confirmation of acetylcholine detection mechanism was elucidated by XPS, where the acetylcholine interaction resulted in a decrease in the % (dPIn doping level and an increase of the dPIn structural defect. The response optimizations with dPIn concentrations, applied potentials, and incubation times were systematically investigated. The 45dPIn-15MWCNT operated at + 0.6 V vs. Ag/AgCl with 5 min of incubation time was the optimum condition to obtain the highest acetylcholine current response. Chronoamperometric acetylcholine detection revealed two distinct current regimes from the acetylcholine surface interaction and the de-doping of dPIn. Regime I was related to the diffusion-controlled process as observed in the low concentration range of 10−8–10−5 M. Regime II corresponded to the mixed diffusion-controlled and adsorption-controlled process as observed in the concentration range of 10−5–10−2 M. For regime I, the calculated LOD was as low as 1.27 nM with a very high acetylcholine response sensitivity. Regime I is suggested for the point-of-care utility, where the detectable concentration range covered the acetylcholine level normally found in the healthy human blood. Regime II can be applicable and useful in the treatment monitoring of neurological diseases.