Tuning Catalytic Activity of Nanozymes: History
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Contributor:
Miaomiao Wang
,
Ping Zhu
,
Shuge Liu
,
Yating Chen
,
Dongxin Liang
,
Yage Liu
,
Wei Chen
,
Liping Du
,
Chunsheng Wu
Nanozymes are alternatives to natural enzymes but remain slightly inferior in catalytic activity. Thus, it is necessary to focus on several important factors that affect the enzymatic activity of nanozymes as well as strategies to enhance activity, thereby laying a theoretical foundation for the design of nanozymes. One of the distinct features of enzymes are their ultrahigh reaction rate. Correspondingly, nanozymes with comparable or even superior activity are long-standing pursuits.
  • nanozyme
  • sensing
  • monitoring

1. Size and Shape

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. [1] 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. [2] 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. [3] 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. [4] 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. [5]. According to the typical Michaelis–Menten curve obtained for VO2 nanozymes, the apparent KM 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.

2. Composition and Doping

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 [6], 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. [7] 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. [8] 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. [9] 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.

3. Surface Coating

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 [10]. 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. [11] 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. [12] 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. [13] 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 superoxide dismutase (SOD) and catalase-like activity, which compromise the multifunctional property of chitosan nanoparticles (CSNPs).

4. Other Factors

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. [12] 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. [14] 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. [15] 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.

This entry is adapted from the peer-reviewed paper 10.3390/bios13030314

References

  1. Valden, M.; Lai, X.; Goodman, D.W. Onset of catalytic activity of gold clusters on titania with the appearance of nonmetallic properties. Science 1998, 281, 1647–1650.
  2. Zhou, X.C.; Xu, W.L.; Liu, G.K.; Panda, D.; Chen, P. Size-Dependent Catalytic Activity and Dynamics of Gold Nanoparticles at the Single-Molecule Level. J. Am. Chem. Soc. 2010, 132, 138–146.
  3. Kalantari, M.; Ghosh, T.; Liu, Y.; Zhang, J.; Zou, J.; Lei, C.; Yu, C.Z. Highly Thiolated Dendritic Mesoporous Silica Nanoparticles with High-Content Gold as Nanozymes: The Nano-Gold Size Matters. Acs Appl. Mater. Interfaces 2019, 11, 13264–13272.
  4. Biswas, S.; Tripathi, P.; Kumar, N.; Nara, S. Gold nanorods as peroxidase mimetics and its application for colorimetric biosensing of malathion. Sens. Actuators B-Chem. 2016, 231, 584–592.
  5. Tian, R.; Sun, J.H.; Qi, Y.F.; Zhang, B.Y.; Guo, S.L.; Zhao, M.M. Influence of VO2 Nanoparticle Morphology on the Colorimetric Assay of H2O2 and Glucose. Nanomaterials 2017, 7, 347.
  6. Wu, J.J.X.; Wang, X.Y.; Wang, Q.; Lou, Z.P.; Li, S.R.; Zhu, Y.Y.; Qin, L.; Wei, H. Nanomaterials with enzyme-like characteristics (nanozymes): Next-generation artificial enzymes (II). Chem. Soc. Rev. 2019, 48, 1004–1076.
  7. Zhu, W.; Cheng, Y.; Yan, S.; Chen, X.; Wang, C.; Lu, X. A general cation-exchange strategy for constructing hierarchical TiO2/CuInS2/CuS hybrid nanofibers to boost their peroxidase-like activity toward sensitive detection of dopamine. Microchem. J. 2022, 183, 108090.
  8. Feng, X.Y.; Fu, H.; Bai, Z.Y.; Li, P.; Song, X.L.; Hu, X.P. Colorimetric detection of glucose by a hybrid nanomaterial based on amplified peroxidase-like activity of ferrosoferric oxide modified with gold-platinum heterodimer. New J. Chem. 2021, 46, 239–249.
  9. Zhao, L.; Ren, X.; Zhang, J.; Zhang, W.; Chen, X.; Meng, X. Dendritic silica with carbon dots and gold nanoclusters for dual nanozymes. New J. Chem. 2020, 44, 1988–1992.
  10. Liu, B.W.; Liu, J.W. Surface modification of nanozymes. Nano Res. 2017, 10, 1125–1148.
  11. Lee, A.H.Y.; Kang, W.S.; Choi, J.S. Highly Enhanced Enzymatic Activity of Mn-Induced Carbon Dots and Their Application as Colorimetric Sensor Probes. Nanomaterials 2021, 11, 3046.
  12. Sun, S.X.; Zhang, Z.J.; Xiang, Y.; Cao, M.W.; Yu, D.Y. Amino Acid-Mediated Synthesis of the ZIF-8 Nanozyme That Reproduces Both the Zinc-Coordinated Active Center and Hydrophobic Pocket of Natural Carbonic Anhydrase. Langmuir 2022, 38, 1621–1630.
  13. Jain, V.; Bhagat, S.; Singh, M.; Bansal, V.; Singh, S. Unveiling the effect of 11-MUA coating on biocompatibility and catalytic activity of a gold-core cerium oxide-shell-based nanozyme. RSC Adv. 2019, 9, 33195–33206.
  14. Gao, L.Z.; Liu, Y.; Kim, D.; Li, Y.; Hwang, G.; Naha, P.C.; Cormode, D.P.; Koo, H. Nanocatalysts promote Streptococcus mutans biofilm matrix degradation and enhance bacterial killing to suppress dental caries in vivo. Biomaterials 2016, 101, 272–284.
  15. Li, D.D.; Guo, Q.Q.; Ding, L.M.; Zhang, W.; Cheng, L.; Wang, Y.Q.; Xu, Z.B.; Wang, H.H.; Gao, L.Z. Bimetallic CuCo2S4 Nanozymes with Enhanced Peroxidase Activity at Neutral pH for Combating Burn Infections. Chembiochem 2020, 21, 2620–2627.
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