Blood compatibility and extended linearity of lactate enzyme electrode using poly(vinyl chloride) outer membranes

A functionally haemocompatible lactate enzyme electrode system with an extended linear range has been developed. The electrode is based on classical amperometric detection of hydrogen peroxide produced by the enzyme lactate oxidase, immobilised in a glutaraldehyde matrix. The sensor system comprises an outer poly(vinyl chloride), PVC, membrane with incorporated non-ionic surfactant which acts both as a haemocompatible interface and a diffusion barrier, extending the sensor linear range up to at least 90 mM lactate. Electroactive interferents, such as ascorbate, urate and acetaminophen, are effectively excluded by the further use of an inner sulphonated polyether-ether sulphone/polyether sulphone membrane. Membrane composition and fabrication were investigated. The blood compatibility of the outer PVC membranes was evaluated by comparing sensitivity of the electrode before and after exposure to undiluted whole blood. Scanning electron microscopy (SEM) was also used to examine the membrane surface. Measurements of whole blood and plasma lactate concentrations when compared with those obtained with a standard lactate analyser gave, respectively, y = 1.2x + 0.50, r2 = 0.97, n = 6 and y = 0.89x + 0.13, r2 = 0.96, n = 20.