A liposomal enzyme electrode for measuring glucose.

Enzyme electrodes have been described for measuring glucose but have been limited by the saturation kinetics of the glucose oxidase not allowing clinically relevant glucose concentrations to be measured (0-25 mM). One way of alleviating this problem is to use diffusion-controlled membranes which result in the enzyme experiencing a smaller substrate concentration than that of the bulk solution. As an extension of this concept we have encapsulated glucose oxidase in liposomes whereby the lipid bilayer wall provides the diffusion-limiting membrane as well as providing a biocompatible layer which is of particular relevance when blood glucose is to be measured. Linear ranges were found to embrace the required glucose concentrations and moreover by using liposomes prepared from different lipids, e.g., dimyristoyl (14:0) phosphatidylcholine (DMPC), dipalmitoyl (16:0) phosphatidylcholine (DPPC) and distearoyl (18:0) phosphatidylcholine (DSPC), the electrode response was shown to depend on the bilayer permeabilities in relation to the lipid phase transition temperatures and as a consequence the linear ranges were duly altered.