Direct determination of glucose in serum by fluorimetry using a labeled enzyme

In this paper we propose the use of derivatized glucose oxidase (GOx) with fluorescein-5(6)-carboxamido-caproic acid ester (FS) for the direct fluorometric determination of glucose in blood serum. This method is based on the modification of the fluorescence of GOx-FS (lambda(excitation)=489 nm and lambda(emission)=520 nm) with the analyte concentration during its enzymatic reaction with the glucose. This makes a second enzymatic reaction unnecessary. The mechanism by which the change in the fluorescence of GOx-FS takes place is discussed and a mathematical equation which models the process is given. The derivatization and measurement conditions were optimized: in the optimum conditions GOx-FS is stable for at least 3 weeks, the detection limit obtained is 85 mg l(-1) and the precision 2.5% (n=9). The results were compared with those obtained by a commercial clinical analyzer and no systematic errors were observed. (C) 2000 Elsevier Science B.V. All rights reserved.