CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, People's Republic of China.
University of the Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
Nanotechnology. 2021 Sep 6;32(48). doi: 10.1088/1361-6528/ac1e53.
Surface chemistry control is a key means to improve substrate selectivity and enhance catalytic activity of nanozymes, a kind of novel artificial enzymes. Herein, we demonstrated that apart from chemical properties of functional groups, their spatial distance to the catalytic sites is also very important to improve the catalytic performance of nanozymes. Using cetyltrimethylammonium bromide (CTAB) coated gold nanorods (AuNR) as the example, we showed that cysteine (Cys) surface modification can greatly enhance the peroxidase activity of AuNR for the oxidation of substrate 3,3',5,5'-tetramethylbenzidine (TMB). By using cysteine derivatives, the key role of the carboxylic group in cysteine is revealed in improving substrate binding and activity enhancement. The electrostatic interactions of carboxylic groups from adsorbed cysteine molecules with protonated amino groups of TMB bring TMB molecules to the surface Au active sites and thus markedly increase catalytic activity. In contrast, despite having two carboxylic groups, glutathione (GSH) surface modification only leads to quite limited improvement of catalytic activity. We speculated that due to large molecular size of GSH, the spatial distance between TMB-GSH and Au is larger than that between TMB-Cys and Au. Furthermore, Raman characterization indicated that at high Cys coverage, they form patches on rod surface via zwitterionic interactions, which may give additional benefits by decreasing the steric hindrance of TMB diffusion to surface Au atom sites. In all, our study highlights the importance of fine surface tuning in the design of nanozymes.
表面化学控制是提高纳米酶（一种新型人工酶）底物选择性和增强催化活性的关键手段。本文中，我们证明了除了官能团的化学性质外，它们与催化位点的空间距离对于提高纳米酶的催化性能也非常重要。以十六烷基三甲基溴化铵（CTAB）包覆的金纳米棒（AuNR）为例，我们表明半胱氨酸（Cys）表面修饰可以极大地增强 AuNR 的过氧化物酶活性，从而氧化底物 3,3',5,5'-四甲基联苯胺（TMB）。通过使用半胱氨酸衍生物，揭示了半胱氨酸中羧酸基团在提高底物结合和增强活性方面的关键作用。吸附的半胱氨酸分子的羧酸基团与 TMB 的质子化氨基之间的静电相互作用将 TMB 分子带到表面 Au 活性位点，从而显著增加催化活性。相比之下，尽管具有两个羧酸基团，但谷胱甘肽（GSH）表面修饰仅导致催化活性的相当有限的提高。我们推测，由于 GSH 的分子尺寸较大，TMB-GSH 和 Au 之间的空间距离大于 TMB-Cys 和 Au 之间的距离。此外，拉曼表征表明，在高 Cys 覆盖率下，它们通过两性离子相互作用在棒状表面形成斑块，这可能通过降低 TMB 向表面 Au 原子位点扩散的空间位阻来提供额外的益处。总之，我们的研究强调了在纳米酶设计中精细表面调谐的重要性。
