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 ∼57% of applied GmOx (0.30–3.0 units). The CHIT + GmOx based biosensor displayed a low detection limit of 1.0 × 10−7 M MSG (S/N = 3, E = 0.400 V), linear range up to 2 × 10−4 M (R2 = 0.991), sensitivity of 85 mA M−1 cm−2, and a short response time (t90% = 2 s). The biosensors maintained ∼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 °C, the CHIT + GmOx films retained ∼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.