In this paper we propose the use of derivatized glucose oxidase (GOx) with
fluorescein-5(6)-carboxamido-caproic acid ester (FS) for the direct fluorom
etric determination of glucose in blood serum. This method is based on the
modification of the fluorescence of GOx-FS (lambda(excitation)=489 nm and l
ambda(emission)=520 nm) with the analyte concentration during its enzymatic
reaction with the glucose. This makes a second enzymatic reaction unnecess
ary. 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 li
mit 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 syste
matic errors were observed. (C) 2000 Elsevier Science B.V. All rights reser
ved.