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 acti vity of the enzyme following exposure to organophosphates and a carbamate p esticide was measured by electrochemically monitoring the rate of hydrolysi s of acetyl thiocholine iodide. Three polymers were used to form a matrix f or the cholinesterase on the electrodes: hydroxyethyl cellulose, a co-polym er of vinyl pyrrolidone and dimethylaminoethyl methacrylate, and polyethyle neimine. Electrodes were exposed to drops of water or pesticide solution, d ried and their activity assessed 24 h later. The activity at that time was generally proportional to the dose but when the enzyme matrix was hydroxyet hyl cellulose, electrode activity was inhibited by water as well as by pest icides. When the matrix was the co-polymer, the electrodes only showed sign ificant responses to pesticide. This could allow electrode activity to be c onveniently assessed some time after exposure to pesticide, as it circumven ts the necessity for incubation of pesticide and electrode at the time of t he assay. The long-term storage stability of electrodes was highest when th e enzyme matrix consisted of the co-polymer, the electrodes retaining their activity for nearly a year. In comparison, the activities of electrodes ma de using hydroxyethyl cellulose or polyethyleneimine quickly fell to low le vels. (C) 1998 Elsevier Science S.A. All rights reserved.