Yuan Bo, Chou Hung-Lung, Peng Yung-Kang
Department of Chemistry, City University of Hong Kong, Hong Kong 0000, Hong Kong SAR.
Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 10617, Taiwan.
ACS Appl Mater Interfaces. 2021 Oct 12. doi: 10.1021/acsami.1c13429.
Since FeO was reported to mimic horseradish peroxidase (HRP) with comparable activity (2007), countless peroxidase nanozymes have been developed for a wide range of applications from biological detection assays to disease diagnosis and biomedicine development. However, researchers have recently argued that FeO has no peroxidase activity because surface Fe(III) cannot oxidize tetramethylbenzidine (TMB) in the absence of HO (cf. HRP). This motivated us to investigate the origin of transition metal oxides as peroxidase mimetics. The redox between their surface M (oxidation) and HO (reduction) was found to be the key step generating OH radicals, which oxidize not only TMB for color change but other HO to produce HO radicals for M regeneration. This mechanism involving free OH and HO radicals is distinct from that of HRP with a radical retained on the Fe-porphyrin ring. Most importantly, it also explains the origin of their catalase-like activity (i.e., the decomposition of HO into HO and O). Because the production of OH radicals is the rate-limiting step, the poor activity of FeO can be attributed to the slow redox of Fe(II) with HO, which is two orders of magnitude slower than the most active Cu(I) among common transition metal oxides. We further tested glutathione (GSH) detection on the basis of its peroxidase-like activity to highlight the importance of understanding the mechanism when selecting materials with high performance.
自2007年有报道称FeO可模拟辣根过氧化物酶（HRP）且具有相当的活性以来，已经开发出了无数种过氧化物酶纳米酶，用于从生物检测分析到疾病诊断和生物医学开发等广泛的应用领域。然而，研究人员最近认为FeO没有过氧化物酶活性，因为在没有H₂O₂的情况下，表面的Fe(III)无法氧化四甲基联苯胺（TMB）（与HRP相比）。这促使我们研究过渡金属氧化物作为过氧化物酶模拟物的起源。发现它们表面的M（氧化）与H₂O₂（还原）之间的氧化还原反应是产生羟基自由基的关键步骤，这些羟基自由基不仅能氧化TMB以实现颜色变化，还能氧化其他H₂O₂以产生用于M再生的过氧化氢自由基。这种涉及游离羟基和过氧化氢自由基的机制与HRP不同，HRP的自由基保留在铁卟啉环上。最重要的是，它还解释了它们类似过氧化氢酶活性的起源（即H₂O₂分解为H₂O和O₂）。由于羟基自由基的产生是限速步骤，FeO活性较差可归因于Fe(II)与H₂O₂的氧化还原反应缓慢，这比常见过渡金属氧化物中活性最高的Cu(I)慢两个数量级。我们基于其类似过氧化物酶的活性进一步测试了谷胱甘肽（GSH）检测，以突出在选择高性能材料时理解机制的重要性。
