Multienzyme microbiosensor based on electropolymerized o-phenylenediamine for simultaneous in vitro determination of acetylcholine and choline

► Poly(o-phenylenediamine) (PoPD) electropolymerized carbon fibre electrode. ► Sensitivity towards Ch (6.3 ± 0.3 μA mM−1) and ACh (5.8 ± 0.3 μA mM−1). ► Linear range for Ch (KM = 0.52 ± 0.03 mM) and ACh (0.59 ± 0.07 mM). ► Fast response time of <5 s with 0.045 μM limit of detection. ► Studies on different ratio (ACh/Ch) revealed that 10:1(10) gave best overall response.