An Improved Amperometric D-amino Acid Biosensor Based on Immobilization of D-Amino Acid Oxidase on Nanocomposite of Chitosan/Fe3O4NPs/ cMWCNT/GC Electrode

Objective: An improved amperometric D aminoacid (DAA) biosensor was fabricated by immobilizing covalently, D-amino acid oxidase (DAAO) onto nanocomposite of chitosan (CHIT)/ iron oxide nanoparticles (Fe3O4NPs)/ carboxylated multiwalled carbon nanotubes (cMWCNT)/ electrodeposited onto glassy carbon (GC) electrode. Methods: The iron oxide nanoparticles (Fe3O4NPs) were prepared and characterized by UV spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Results: The enzyme electrode (DAAO/CHIT/ Fe3O4NPs/cMWCNT/GC) was characterized by scanning electron microscopy (SEM), FTIR and electrochemical impedance spectroscopy (EIS). The biosensor showed maximum response within 2s at pH 8.0, 35°C and potential of 0.09V vs. Ag/AgCl with a linear working range of 0.02-0.80 μM, sensitivity of 919.29 μAcm^-2μM^-1 and detection limit of 0.02 μM. Conclusion: The within and between batch coefficients of variation (CVs) for determination of DAA by present biosensor were 2.35% and 2.87%, respectively. The level of DAA in real fruit juices as measured by the present biosensor matched with those by the standard spectrophotometric method with a good correlation (r = 0.978). The biosensor lost 30 % of its initial activity over a period of 120 days when stored dry at 4°C.