| Summary: | Xanthine biosensor based on glassy carbon electrode (GC) modified with graphene (GR), Co3O4 nanoparticles and chitosan (CH) composite was fabricated. Xanthine oxidase (XAO) solution was dropped on the surface of Co3O4/CH/GR/GC and electrode was placed in saturated glutaraldehyde vapor for the crosslinking of the enzymes. The modified electrode was characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimized experimental conditions, xanthine was detected in the concentration range from 5.0×10-7 to 8.0×10-5 M with a detection limit of 2.0×10-7 M. The low Michaelis–Menten constant (0.17 mM) suggested enhanced enzyme affinity for the immobilized enzyme as compared to previously reported xanthine biosensors. Moreover, the biosensor exhibited some advantages, such as short response time (10 s), high sensitivity (6.58 μA/mM or 74.8 µA/mMcm2) and good reproducibility (RSD = 1.2%). The suitability of the device was verified by xanthine assay in a fish meat. The biosensor provide to be a reliable, easy, fast and economical method for the evaluation of fish freshness.
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