Regulation Of Catalytic Activities Of Nanozymes

The activities of nanozymes can be tuned by many factors, such as size, morphology, surface modification, composition, pH and temperature, as well as ions or molecules.

• Size. The catalytic performance of nanozymes is related to the size of materials. Generally, the smaller the size of the nanozyme and the larger the specific surface area, the more it can bind to the substrate, resulting in stronger activity. In 2007, Yang, Perrett and co-workers studied the catalytic activity of Fe₃O₄ nanoparticles (NPs) of different sizes. They selected 30, 150 and 300 nm Fe₃O₄ NPs. Experimental data showed that 30 nm Fe₃O₄ NPs had the highest peroxidase (POD)-like activity, while 300 nm Fe₃O₄ NPs showed the lowest catalytic activity^[1].

• Shape And Morphology. The biocatalytic performance of nanozyme is also tunable by controlling the shape as well as morphology. For instance, iron oxide nanozymes of different shapes have different POD activities. Iron oxide nanoclusters have higher POD activity than iron oxide nanoflowers, while iron oxide nanosquares have the lowest POD activity. For Co₃O₄ nanozymes, Co₃O₄ nanosheets have the highest POD activity, followed by Co₃O₄ nanopolyhedra and nanorods, and Co₃O₄ nanocubes have the lowest POD activity. Furthermore, cubic, polyhedral and hexagonal Mn₃O₄ nanozymes showed lower superoxide dismutase (SOD) activity than flower-like Mn₃O₄ nanozymes. Octahedral Pd NPs have stronger antioxidant capacity than tetrahedral Pd NPs.

• Surface Modification. Surface modification, including the thickness of coating, functional group, as well as surface charges can also influence the catalytic abilities of nanozymes. For example, Lin and Chen's group explored differences in the POD-like properties of Au NPs with different surface modifications. They selected unmodified, amino-modified, and citrate-modified Au NPs for comparison. They found that unmodified Au NPs exhibited excellent catalytic activity compared with other Au NPs. In addition, when 3,3',5,5'-tetramethylbenzidine (TMB) was selected as the substrate, the citrate-modified Au NPs exhibited higher POD-like activity than the amino-modified Au NPs. This phenomenon was completely reversed when 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) was chosen as the substrate^[2].

• Composition. The catalytic activities of nanozymes can also be regulated by changing the proportion of components in the nanomaterials. In addition, doping some component into nanozymes has been proved as an efficient method for regulating the activities of nanozymes. For example, CuO NPs have low catalytic efficiency as POD nanozymes. Nagvenkar and Gedanken used Zn-doped CuO NPs to form nanocomposite (Zn-CuO) NPs to enhance their catalytic activity^[3].

• pH and Temperature. The surrounding pH can also influence the catalytic properties on nanozymes. For example, under acidic condition, Au NPs can be considered as POD candidates while in neutral or alkaline conditions, Au NPs will exhibit catalase (CAT)- or SOD-like catalytic properties. Similarly, temperature may also have a great effect on the catalytic performance of nanozymes.

• Ions or Molecules. Ions and some molecules can act as modulators to modulate the catalytic properties of nanozymes. For example, sulfide ions could influence the POD-like property of β-casein-stabilized Pt NP (CM-PtNP). Experimental data illustrated that when using different reaction substrates, sulfide ions could exhibit different regulation effect on the POD-like activity of CM-PtNP^[4].

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