Construction of a simple optical sensor based on air stable lipid film with incorporated urease for the rapid detection of urea in milk

This work describes the construction of a simple optical sensor for the rapid, selective and sensitive detection of urea in milk using air stable lipid films with incorporated urease. The lipid film is stabilized on a glass filter by polymerization using UV (ultra-violet) radiation prior its use. Methacrylic acid was the functional monomer, ethylene glycol dimethacrylate was the crosslinker and 2,2′-azobis-(2-methylpropionitrile) was the initiator. Urease is incorporated within this mixture prior to the polymerization. The presence of the enzyme in these films quenched this fluorescence and the colour became similar to that of the filters without the lipid films. A drop of aqueous solution of urea provided a “switching on” of the fluorescence which allows the rapid detection of this compound at the levels of 10−8 M concentrations. The investigation of the effect of potent interferences included a wide range of compounds usually found in foods and also of proteins and lipids. These lipid membranes were used for the rapid detection of urea in milk.