Sensitive detection of copper ions (Cu²⁺) in biological samples is extremely important since an abnormal level of Cu²⁺ is linked with many diseases. Herein, we demonstrated a novel turn-on colorimetric sensor for selective detection of Cu²⁺ both in buffered solution and serum samples based on porous bimetallic transition metal oxide nanocages (ZnO-Co₃O₄ NCs) as peroxidase mimics. The ZnO-Co₃O₄ NCs were prepared by using ZnCo-zeolitic-imidazolate-framework (ZnCo-ZIF) as precursors via direct calcination. With the high peroxidase-like activity, the obtained ZnO-Co₃O₄ NCs can catalyze the oxidation of tetramethylbenzidine (TMB) in the presence of H₂O₂ to form a blue colored product. The inhibition effect of cysteine (Cys) on the catalytic activity of ZnO-Co₃O₄ NCs and its strong binding ability toward Cu²⁺ enabled the ZnO-Co₃O₄ NCs/Cys system to be utilized for sensitive detection of Cu²⁺, in which the catalytic activity of ZnO-Co₃O₄ NCs/Cys can be recovered by the introduction of Cu²⁺ with an obvious color change of the solution. The linear range for Cu²⁺ determination was 2 to 100 nM with a detection limit of 1.08 nM. More importantly, this colorimetric sensor has been successfully applied to detect Cu²⁺ in serum without pretreatment. Our findings are expected to expand the scope of application of nanozyme and shed light on early disease diagnosis.

中文翻译：

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MOF衍生的多孔ZnO-Co3O4纳米笼作为过氧化物酶模拟物用于比色检测血清中的铜（II）离子

敏感地检测生物样品中的铜离子（Cu ²⁺）非常重要，因为Cu ²⁺的异常水平与许多疾病有关。在这里，我们展示了一种新型的开启式比色传感器，用于基于过氧化物酶模拟的多孔双金属过渡金属氧化物纳米笼（ZnO-Co ₃ O ₄ NCs）选择性检测缓冲溶液和血清样品中的Cu ²⁺。ZnO-Co ₃ O ₄ NCs是通过直接煅烧以ZnCo-沸石-咪唑盐骨架（ZnCo-ZIF）为前体制备的。具有高的过氧化物酶样活性，得到的ZnO-Co ₃ O ₄NC在H ₂ O ₂存在下可以催化四甲基联苯胺（TMB）的氧化，形成蓝色产物。半胱氨酸（Cys）对ZnO-Co ₃ O ₄ NCs的催化活性的抑制作用及其对Cu ^2+的强结合能力使ZnO-Co ₃ O ₄ NCs / Cys系统可用于敏感检测Cu ^{2 +}，其中可以通过引入Cu ²⁺来恢复ZnO-Co ₃ O ₄ NCs / Cys的催化活性，并且溶液的颜色会发生明显变化。Cu ²⁺的线性范围测定值为2至100 nM，检出限为1.08 nM。更重要的是，该比色传感器无需预处理即可成功应用于检测血清中的Cu ²⁺。我们的发现有望扩大纳米酶的应用范围，并为早期疾病诊断提供启示。