Stability and function of screen printed electrodes, based on cholinesterase, stabilised by a co-polymer/sugar alcohol mixture

Electrodes containing cholinesterase were made by screen-printing. The activity of the enzyme following exposure to organophosphates and a carbamate pesticide was measured by electrochemically monitoring the rate of hydrolysis of acetyl thiocholine iodide. Three polymers were used to form a matrix for the cholinesterase on the electrodes: hydroxyethyl cellulose, a co-polymer of vinyl pyrrolidone and dimethylaminoethyl methacrylate, and polyethyleneimine. Electrodes were exposed to drops of water or pesticide solution, dried and their activity assessed 24 h later. The activity at that time was generally proportional to the dose but when the enzyme matrix was hydroxyethyl cellulose, electrode activity was inhibited by water as well as by pesticides. When the matrix was the co-polymer, the electrodes only showed significant responses to pesticide. This could allow electrode activity to be conveniently assessed some time after exposure to pesticide, as it circumvents the necessity for incubation of pesticide and electrode at the time of the assay. The long-term storage stability of electrodes was highest when the enzyme matrix consisted of the co-polymer, the electrodes retaining their activity for nearly a year. In comparison, the activities of electrodes made using hydroxyethyl cellulose or polyethyleneimine quickly fell to low levels. (C) 1998 Elsevier Science S.A. All rights reserved.