Biosensors for choline, choline esters and inhibitors of choline esterase

Abstract A choline electrode has been developed by coupling immobilized choline oxidase to a hydrogen peroxide electrode. The co-immobilization of cholinesterase permits acetylcholine to be measured. The excess of both enzymes results in a diffusion-limited electrode response for both substrates, with relative sensitivities 1: 0.6 for choline compared with acetylcholine. When a kinetically controlled bienzyme sensor with a low activity of cholinesterase is used, a diminished sensitivity is obtained for acetylcholine with an increased sensitivity of inhibitors such as NaF, butoxycarboxime, trichlorfon or dimethoate. Potentially disposable sensors for those inhibitors have been constructed with cholinesterase co-immobilized with choline oxidase in a gelatin membrane on a platinum electrode and with cholinesterase immobilized in polyurethane on a thick-film metallized platinum electrode. The decreased formation rate of thiocompounds from thiocholinesters serves as a measure for the inhibited enzyme in the latter set-up.