Nanozymes: Definition, Activity, and Mechanisms

TLDR

Nanozymes are catalysts—ranging from immobilized inorganic metal complexes and enzymes to inorganic nanoparticles—whose definition is evolving, with type 1 involving immobilized catalysts on nanomaterials (dominant 2004–2014) and type 2 relying on surface catalytic properties of inorganic nanomaterials (dominant since 2014), and growing research seeks to understand their mechanisms for rational engineering. The authors aim to broaden the definition of nanozymes to spur application‑based research that replaces enzymes with nanomaterials in analytical, environmental, and biomedical contexts, and to clarify what constitutes a nanozyme unit for comparison with enzymes. The study reviews the history of nanozymes, distinguishing two main types, and presents four definitions of a nanozyme unit, illustrated by comparing iron‑oxide and horseradish peroxidase activities. The authors conclude by outlining future perspectives for the nanozyme field.

Abstract

Abstract “Nanozyme” is used to describe various catalysts from immobilized inorganic metal complexes, immobilized enzymes to inorganic nanoparticles. Here, the history of nanozymes is dvescribed in detail, and they can be largely separated into two types. Type 1 nanozymes refer to immobilized catalysts or enzymes on nanomaterials, which were dominant in the first decade since 2004. Type 2 nanozymes, which rely on the surface catalytic properties of inorganic nanomaterials, are the dominating type in the past decade. The definition of nanozymes is evolving, and a definition based on the same substrates and products as enzymes are able to cover most currently claimed nanozymes, although they may have different mechanisms compared to their enzyme counterparts. A broader definition can inspire application‐based research to replace enzymes with nanomaterials for analytical, environmental, and biomedical applications. Comparison with enzymes also requires a clear definition of a nanozyme unit. Four ways of defining a nanozyme unit are described, with iron oxide and horseradish peroxidase activity comparison as examples in each definition. Growing work is devoted to understanding the catalytic mechanism of nanozymes, which provides a basis for further rational engineering of active sites. Finally, future perspective of the nanozyme field is discussed.