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 (Fe3O4)/ carboxylated multiwalled carbon nanotubes (cMWCNT)/ electrodeposited onto glassy carbon (GC) electrode. Methods: The iron oxide nanoparticles (Fe3O4) were prepared and characterized by UV spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Results: The enzyme electrode (DAAO/CHIT/ Fe3O4/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.

中文翻译：

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基于壳聚糖/Fe3O4NPs/cMWCNT/GC电极纳米复合材料固定D-氨基酸氧化酶的改进安培式D-氨基酸生物传感器

目的：通过将 D-氨基酸氧化酶 (DAAO) 共价固定在壳聚糖 (CHIT)/氧化铁纳米粒子 (Fe3O4)/羧化多壁碳纳米管 (cMWCNT)/电沉积纳米复合材料上，制备改进的安培 D 氨基酸 (DAA) 生物传感器。玻碳（GC）电极。方法：制备氧化铁纳米颗粒（Fe3O4），并通过紫外光谱、透射电子显微镜（TEM）和傅里叶变换红外（FTIR）光谱进行表征。结果：通过扫描电子显微镜（SEM）、FTIR和电化学阻抗谱（EIS）对酶电极（DAAO/CHIT/Fe3O4/cMWCNT/GC）进行表征。该生物传感器在 pH 8.0、35°C 和电位 0.09V vs. Ag/AgCl 的条件下在 2 秒内显示出最大响应，线性工作范围为 0.02-0.80 μM，灵敏度为 919.29 μAcm-2μM-1，检测限为 0.02 μM。结论：现有生物传感器测定DAA的批内和批间变异系数(CV)分别为2.35%和2.87%。本生物传感器测得的真实果汁中 DAA 的含量与标准分光光度法测得的结果相符，具有良好的相关性 (r = 0.978)。当在 4°C 干燥保存时，生物传感器在 120 天内失去了 30% 的初始活性。