Amperometric glutamate biosensor based on chitosan enzyme film

A simple method for enzyme immobilization in electrochemical biosensors for monosodium glutamate (MSG) was developed. The method relied on the precipitation of complexes of polyanionic enzyme L-glutamate oxidase (GmOx) with polycationic chains of chitosan (CHIT) on the surface of platinum electrode. Such ionotropic gelation allowed the CHIT matrix to retain similar to 57% of applied GmOx (0.30-3.0 units). The CHIT + GmOx based biosensor displayed a low detection limit of 1.0 x 10(-7) M MSG (S/N = 3, E = 0.400 V), linear range up to 2 x 10(-4) M (R-2 = 0.991), sensitivity of 85 mA M-1 cm(-2), and a short response time (t(90%) = 2 s). The biosensors maintained similar to 80% of the MSG signal even after 11 h of continuous use, which indicated good operational stability. Stability studies revealed that a majority of signal loss was due to a slow transformation of glutamate in a solution into the redox inactive pyroglutamate. After 4 months of storage in water at 4 degrees C, the CHIT + GmOx films retained similar to 80-90% of their original activity toward the MSG. The CHIT + GmOx films are promising candidates for the development of simple and reliable chromatographic detectors for glutamate. (c) 2006 Elsevier Ltd. All rights reserved.