Size, shape, and atomic arrangement can lead to changes in the catalytic performance of materials. It was found that the catalytic activity and stability of nanozyme increased with the increase in surface volume ratio. For example, Valden et al. [33] prepared gold clusters with a diameter of 1 to 6 nm on the single crystal surface of titanium dioxide under ultrahigh vacuum to investigate the size dependence of their low-temperature catalytic oxidation of carbon monoxide. It was found that the gold cluster with the largest carbon monoxide oxidation activity was 3 nm. In another case, Zhou et al. [34] used Au nanoparticles with various sizes (2–15 nm) to catalyze the reduction of resazurin, showing that Au nanoparticles of 6 nm exhibited the highest activity. However, small gold nanoparticles tend to aggregate and lose their activity. Scientists often anchor gold nanoparticles to carbon, silica, graphene, and other supporting materials to improve the dispersion of bare Au. Kalantari et al. [35] adjusted the delayed addition time of the thiolated organosilica precursor to control the nanostructure and the thiol density. Moreover, for the first time, they demonstrated that the peroxidase-like activity of T-Dendritic Mesoporous Silica Microspheres (DMSNs)-Au depended on nano-Au size. In addition, the highest activity was achieved at the Au particle size of 1.9 nm.

The catalytic performance of nanozymes can also be modulated by adjusting the shape of the nanostructures. Biswas et al. [36] compared the catalytic efficiency of gold nanorods (GNRs), gold nanoparticles (GNPs), and horseradish peroxidase (HRP). It was proved that the peroxidase activity of gold nanorods with a length diameter ratio of 2.8 was 2.5 times higher than that of HRP and gold nanoparticles, which showed stability in a wide range of pH and temperature. Based on this, a colorimetric sensor for malathion was developed, whose sensitivity of the assay was 1.78 μg/mL. A comparative study of VO₂ nanoparticles with different morphologies (nanofibers, nanosheets, and nanorods) was conducted and applied to the sensitive colorimetric detection of H₂O₂ and glucose by Tian et al. [37]. According to the typical Michaelis–Menten curve obtained for VO₂ nanozymes, the apparent K_M values of VO₂ nanofibers with H₂O₂ as the substrate were lower than that of VO₂ nanorods and VO₂ nanosheets. It shows that the VO₂ nanofibers have a higher affinity for H₂O₂ compared with VO₂ nanosheets and VO₂ nanorods. Moreover, compared with VO₂ nanorods and VO₂ nanosheets, the VO₂ nanofibers demonstrated the most sensitive response during the H₂O₂ and glucose sensing.

Some researchers have shown, based on the synergistic effect, that combining a variety of nanomaterials or conjugating several nanomaterials to form a hybrid can provide a catalytic center [38], improve the electron transfer between the nanozyme and the substrate, and generate additional active sites, which can adjust the catalytic activity of the catalyst.

Zhu et al. [39] combined TiO₂, CuInS₂, and CuS into a ternary metal sulfide-based hybrid. Owing to the synergistic effect among TiO₂, CuInS₂, and CuS components, compared with the control sample of Fe₃O₄/rGO, TiO₂/rGO, Fe₃O₄, TiO₂, and rGO, the prepared TiO₂/CuInS₂/CuS nanofibers showed excellent peroxidase (POD)-like activity. They subsequently developed a sensor for the detection of dopamine with a detection limit of 1.2 μM. Wang et al. [40] incorporated iron oxide nanoparticles (Fe₃O₄NPs) into the heterodimer composed of gold and platinum to form a hybrid nanomaterial with good peroxidase-like activity. The formation of an alloy between platinum and gold can significantly improve the activity and selectivity of platinum-based catalysts. The nature of the peroxidase-like activity of the Fe₃O₄@Au-Pt hybrid nanomaterial originates from their ability to transfer electrons between the reducing substances and H₂O₂. The colorimetric sensor with a lower detection limit of 0.0018 μM was developed for glucose. Another form of composition is loading. Zhao et al. [41] covalently fixed the carbon point (C-dots) on the inner surface of the amino terminated dendritic silica sphere (dSs) while coupling the gold nanoclusters (Au NCs) on the outer surface. It not only maintains the superoxide dismutase-like enzyme activity of the carbon point but also improves the peroxidase-like-activity of the gold nanoparticles. Furthermore, adjusting the loading ratio of the two kinds of nanozymes can meet different functional requirements.

The surface modification of nanozyme not only plays a connecting role in the combination of nanomaterials but also is of great importance to the regulation of catalytic activity. The surface catalytic reaction process can be described by several basic reaction steps, including substrate adsorption, substrate diffusion on the surface, chemical reaction, and then product desorption to regenerate the active site [42]. Each step will be affected by surface modification. Thus, some general strategies can be adopted for surface modification, such as changing the electronic structure of the surface, regulating the surface acidity, blocking surface contact, promoting product desorption, mediating the exposure of active sites to regulate substrate binding, and applying effective methods for surface electronic structure.

Surface modifiers can be divided into three categories: ions, small molecules, and macromolecules. Lee et al. [43] introduced Mn(acetate)₂ during the synthetic step of N-doped carbon dots to improve the enzymatic properties of metal-induced N-doped carbon dots (N-CDs). Its influence on the enzymatic properties of Mn-induced N-CDs (Mn:N-CDs) was investigated. Finally, the addition of Mn(acetate)₂ to the reaction solution seemed to generate more functional groups at the edge of carbogenic domains in Mn:N-CDs than in N-CDs, resulting in improved peroxidase-like properties. Mn:N-CDs with strong enzymatic effects can be applied as a colorimetric sensor probe for the detection of gamma-aminobutyric acid (GABA). Surface modification can also change the intrinsic enzyme activity of nanomaterials. Zeolitic imidazolate framework-8 (ZIF-8) is a monatomic nanozyme with peroxidase activity. Sun et al. [44] introduced amino acid (AA) to regulate the growth of ZIF-8 crystal, thus simulating the structure and function of natural carbonic anhydrase (CA). Amino acid as a capping agent regulates the shape and size of ZIF-8 and forms a hydrophobic region on the surface of ZIF-8 to simulate the hydrophobic pocket of natural carbonic anhydrase. Compared with natural carbonic anhydrase, Val-ZIF-8 not only has excellent esterase activity but also has better hydrothermal stability. Surface coating may also weaken or even lead to loss of enzyme activity. Jain et al. [45] reported the replacement of cetyl trimithyl ammonium bromide (CTAB) by 11-MUA from the surface of Au-core CeO₂-shell NP-based nanozyme studied for exhibiting multiple enzyme-like activities such as peroxidase, catalase, and superoxide dismutase. They found that 11-MUA coating AuNPs lost the SOD and catalase-like activity, which compromise the multifunctional property of chitosan nanoparticles (CSNPs).

Except regulating the intrinsic enzyme activity of nanozyme to control catalytic activity, external factors can also affect the final enzyme activity. The pH and temperature are the main external influencing factors. A lot of studies have confirmed that acidic conditions are suitable for peroxidase-like activity, while neutral and alkaline conditions are favorable for superoxide dismutase and catalase. For example, the esterase activity of Val-ZIF-8 synthesized by Sun et al. [44] would greatly increase with the increase in temperature. The enzyme activity at 80 °C was about 25 times higher than that at 25 °C. Gao et al. [46] reported a new strategy for controlling plaque biofilm with a peroxidase-like nanozyme (CAT-NP). CAT-NP showed a strong dependence on acidic conditions. It killed 99% of bacteria in the acidic microenvironment simultaneously in a short time for biofilm control and prevention of dental caries. However, several studies have broken through the limitation of optimal pH for different nanozymes. Li et al. [47] developed the copper-based nanozyme (CuCo₂S₄), which showed enhanced peroxidase-like activity and antibacterial ability under neutral conditions. This would be used for infected wounds with pH close to neutral.