Chitosan-glutamate oxidase gels: Synthesis, characterization, and glutamate determination

The biopolymer chitosan (CHIT) was chemically modified with glutaric dialdehyde (GDI) and used for the covalent immobilization of enzyme glutamate oxidase (GmOx). The relationships between the loaded, retained, and active units of GmOx in the CHIT-GDI-GmOx gels were determined by electrochemical assays. The latter indicated that on average ca. 95% of the GmOx was retained in the CHIT-GDI matrix that was loaded with 0.10-3.0 units of the enzyme. The maximum activity of the GmOx immobilized in the gels corresponded to ca. 95% of the activity of the free enzyme. Platinum electrodes coated with CHIT-GDI-GmOx gels (films) were used as amperometric biosensors for glutamate. Such biosensors displayed good operational and long-term stability (at least 11 h and 100 days, respectively) in conjunction with low detection limit of 0.10 mu M glutamate (S/N=3), linear range up to 0.5 mM (R-2 = 0.991), sensitivity of 100 rnA M-1 cm(-2), and short response time (t(90%) = 2 s). This demonstrated an efficient signal transduction in the P-1/CHIT-GDI-GmOx+glutamate system. The CHIT-GDI-GmOx gels constitute a new biosensing element for the development of glutamate biosensors.