Virtually every process in the human body is driven by enzymes, with an estimated 5,000 different types acting as biological catalysts to boost biochemical reactions.
Recognising the potency of such natural enzymes, materials scientists have drawn inspiration to create nanozymes. These nanomaterials, which possess enzyme-like properties, offer advantages such as lower costs, enhanced stability and easier mass production compared to their biological counterparts.
Shibo Xi, a Senior Scientist at A*STAR's Institute of Sustainability for Chemicals, Energy and Environment (ISCE2), has been exploring the promise and potential of single-atom catalysts (SACs). These nanozymes, with their honeycomb-like atomic structures, can serve as alternatives to natural metalloenzymes.
Xi explained that SACs' simple structures (a solitary metal atom supported by another material) are ideal for industrial use, in contrast to the complex, multi-metal compositions of natural metalloenzymes. Nevertheless, SACs' catalytic efficiency and the understanding of their active sites are still catching up to those of metalloenzymes.
Working with researchers from University of Jinan, China; Beijing Institute of Technology, China; and the Technical University of Denmark; Xi and team theorised that fine-tuning the nitrogen atoms around single cobalt atoms in nanozymes may significantly improve the efficiency of these catalysts. These atomic modifications may enhance their oxygen capture and lead to the production of reactive oxygen species, thus more closely mirroring the behaviour of natural enzymes.
The researchers produced a range of single-atom cobalt nanozymes with varying numbers of nitrogen coordination to explore their catalytic activity. The atomic level local structure of the catalysts were characterised using a technique called X-ray absorption fine structure (XAFS). They also employed sophisticated computer modelling (density functional theory), enzyme activity tests and advanced characterisation techniques to observe how nitrogen adjustments influenced the nanozymes’ reaction-accelerating capabilities.
The team's breakthrough came with the discovery that nanozymes coordinated with three nitrogen atoms (Co-N3) displayed the highest oxidase-like activity, generating energetic oxygen particles most effectively. This finding also revealed the mechanisms driving nanozyme activity, notably their ability to attach to oxygen and convert it into reactive oxygen species.
Xi emphasised, “The effect of coordination number on the catalytic performance must be contemplated in the design and refinement of single-atom catalysts for a more efficient and stable catalytic effect.”
These insights can spur innovation in nanozyme design, where high precision, efficiency and stability are achieved by optimising structures on an atomic level. Such advanced knowledge paves the way for developing nanozymes that are not only more potent but can also be customised for specific applications across biomedicine, environmental science, energy conversion and more.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Sustainability for Chemicals, Energy and Environment (ISCE2).
