Co₃O₄ nanoparticles-graphene oxide (Co₃O₄ NPs-GO) nanocomposites with good solubility were successfully synthesized and well characterized. As a nanocatalyst with oxidase-mimicking activity, the nanocomposites can catalyze the oxidation of 3′,5,5′-tetramethylbenzidine (TMB) with high efficiency. The catalyzing reaction was rapid and no extra H₂O₂ was needed compared with other similar TMB oxidation reactions. The catalyzing reaction mechanism of the system was investigated in detail. And it was demonstrated that the oxygen involved in the reaction came from the oxygen absorbed on the nanocomposites which oxidized TMB. Based on this reaction, a colorimetric system for vitamin C detection in vegetable and fruits was established. Under the optimum conditions, the detection can be achieved within 10 min and a linear relationship in concentration range of 2.5 × 10⁻⁶ to 1.8 × 10⁻⁵ M and 3.4 × 10⁻⁵ to 1.7 × 10⁻⁴ M was obtained with a detection limit of 7.0 × 10⁻⁷ M. The colorimetric system exhibited good selectivity, sensitivity and satisfactory recoveries ranged from 93.1% to 101.1%.

成功地合成了具有良好溶解性的Co ₃ O ₄纳米颗粒-氧化石墨烯（Co ₃ O ₄ NPs - GO）纳米复合材料。作为具有氧化酶模拟活性的纳米催化剂，纳米复合材料可以高效催化3'，5,5'-四甲基联苯胺（TMB）的氧化。催化反应迅速，没有多余的H ₂ O ₂与其他类似的TMB氧化反应相比，它是必需的。详细研究了该体系的催化反应机理。并且证明了反应中涉及的氧来自氧化TMB的纳米复合材料上吸收的氧。基于该反应，建立了用于蔬菜和水果中维生素C检测的比色系统。在最佳条件下，可以在10分钟内完成检测，并在2.5×10 ^-6至1.8×10 ^-5  M和3.4×10 ^-5至1.7×10 ^-4  M的浓度范围内获得线性关系。检出限为7.0×10 ^-7 M.比色系统显示出良好的选择性，灵敏度和令人满意的回收率，回收率在93.1％至101.1％之间。