Hydroquinone Substrates for Electrochemical Assays

The activity of enzyme leukocyte esterase (LE) has been commonly used as a proxy for the presence of active leukocytes in the diagnosis of infections. The LE has been typically analyzed by using commercial ELISA kits and kinetic assays to determine its concentration and activity, respectively. Dominant are the studies of clinical utility of existing commercial LE kits and strips, which are all based on the optical detection. Most of the LE assays are qualitative or semiquantitative and rely on reactions that yield products, which subsequently react with additional chemicals to produce a color change proportional to the activity of esterase. While such test strips have been fairly useful, they may have a limited utility in color/opaque solutions. In addition, with only four available color intensity increments, the resolution of differences in LE is often uncertain. The University of Texas at San Antonio researchers have developed a quantitative electrochemical LE assay as a high-resolution alternative to optical LE assays. The concept of the assay is based on a new type of LE substrate that releases a redox-active fragment whose oxidation at an electrode provides a numerical measure of LE activity. The newly designed LE substrate has been used for the determination of esterolytic activity of leukocyte suspensions in buffers and saliva samples via the internally calibrated electrochemical continuous enzyme assay. Christine Burke christine.burke@utsa.edu (210) 458-8140