Estimation of lactate in meat extracts by screen-printed sensors

Various facets of sensor technology: platinum dispersed on carbon, a second "blank" working electrode, polymer matrices for enzymes and diffusion-limiting membranes, were integrated using screen-printing to produce lactate sensors. The enzyme was lactate oxidase. The polymer matrices were hydroxyethyl cellulose, GafQuat/lactitol and hydroxyethyl cellulose/polyethyleneimine. The outer membrane was of known composition: polyvinyl chloride co-polymer/cellulose acetate butyrate. When the sensors were mounted in a flow injection analyser, estimates were obtained of the lactate concentration in simple buffer extracts of cattle meat. The most accurate estimates were obtained from sensors in which the enzyme was embedded in a matrix of GafQuat/lactitol or hydroxyethyl cellulose/polyethyleneimine. The currents generated by the enzyme in the matrices containing GafQuat or polyethyleneimine were higher than when hydroxyethyl cellulose alone was used as a matrix. The activity of the sensors under dry storage (over silica gel at 25 degrees C) varied over eight months, but remained at a functional level. Every step in these relatively simple sensors was achieved by screen-printing; the use of a "blank" working electrode avoided the necessity of additional layers or membranes to reject interferents and the flow injection analyser provided a constant hydrodynamic environment for sensor function. (C) 1999 Elsevier Science B.V. All rights reserved.