Novel fiber-optic biosensor based on immobilized glutathione S-transferase and sol-gel entrapped bromcresol green for the determination of atrazine

The aim of this work was to investigate, for the first time, the potential of the enzyme glutathione S-transferase I (isoenzyme GST-I) for uses in analytical chemistry. A novel fiber-optic biosensor for the detection and determination of the triazine herbicide atrazine was developed based on maize GST-I expressed in E. coli. The sensing bioactive material was a three-layer mini-sandwich. The enzyme was immobilized on the outer layer that consisted of a hydrophilic polyvinylidenefluoride membrane. This membrane was supported on an inner glass disk by means of an intermediate binder sol-gel layer that incorporated bromcresol green (BCG). The biosensor operated in a static mode at 25 degreesC and the rate of the enzymatic reaction, using atrazine as a substrate, served as an analytical signal. A calibration curve was obtained for atrazine, with analytically useful concentration range 2.52-125 muM. The sensor detection limit was 0.84 muM. The reproducibility of atrazine sensing was in the order of +/-3-5%. The method was successfully applied to the determination of this herbicide in real water samples, without sample preparation steps. Atrazine recovery ranged between 85 and 110%. No interference from other pesticides, such as alachlor and carbaryl was observed in the absence of atrazine. The immobilized enzyme retained about 75% of its original activity after 1 month use. Simply unscrewing the terminal holding ring of the probe and placing a new bioactive sandwich could easily replace a deteriorated mini-sandwich. (C) 2002 Elsevier Science B.V. All rights reserved.