Screen-printed carbon electrode for choline based on MnO2 nanoparticles and choline oxidase/polyelectrolyte layers

This paper presents the amperometric biosensor that determines choline and cholinesterase activity using a screen printed graphite electrode. In order to detect H₂O₂ we have blanket modified the electrode material with manganese dioxide nanoparticles layer. Using layer-by-layer technique on the developed hydrogen peroxide sensitive electrode surface choline oxidase was incorporated into the interpolyelectrolyte nanofilm. Its ability to serve as a detector of choline in bulk analysis and cholinesterase assay was investigated. We examined the interferences from red-ox species and heavy metals in the blood and in the environmental sample matrixes. The sensor exhibited a linear increase of the amperometric signal at the concentration of choline ranging from 1.3 × 10⁻⁷ to 1.0 × 10⁻⁴ M, with a detection limit (evaluated as 3σ) of 130 nM and a sensitivity of 103 mA M⁻¹ cm⁻² under optimized potential applied (480 mV vs. Ag/AgCl). The biosensor retained its activity for more than 10 consecutive measurements and kept 75% of initial activity for three weeks of storage at 4 °C. The R.S.D. was determined as 1.9% for a choline concentration of 10⁻⁴ M (n = 10) with a typical response time of about 10 s. The developed choline biosensor was applied for butyrylcholinesterase assay showing a detection limit of 5 pM (3σ). We used the biosensor to develop the cholinesterase inhibitor assay. Detection limit for chlorpyrifos was estimated as 50 pM.