Nanozymes are nanomaterials with enzyme-mimicking catalytic activity. Compared to natural enzymes, nanozymes show various properties such as easy to manufacture, stable, adjustable, and inexpensive. Nanozymes play key roles in biosensing, biocatalysis, and disease treatment. As an important kind of nanozymes, metal-organic framework (MOF)-based nanozymes are receiving a lot of attention due to their structural properties and composition. Rationally developing MOF with enzymes-like catalytic properties has opened new perspectives in biosensing. This review summarizes the up-to-date developments in synthesizing two-dimensional and three-dimensional MOF-based nanozymes and their applications in biosensing. Firstly, classification of nanozymes obtained by MOFs is categorized, and different properties of MOF-based nanozymes are described. Then, the distinctive applications of MOF-based nanozymes in identifying various analytes are thoroughly summarized. Finally, the recent challenges and progressive directions in this area are highlighted.

Oxidative stress is associated with many acute and chronic inflammatory diseases. Development of nanomaterial-based enzyme mimetics for reactive oxygen species (ROS) scavenging is challenging, but holds great promise for the treatment of inflammatory diseases. Herein, we report the highly ordered manganese dioxide encapsulated selenium-melanin (Se@Me@MnO₂) nanozyme with high efficiency for intracellular antioxidation and anti-inflammation. The Se@Me@MnO₂ nanozyme is sequentially fabricated through the radical polymerization and the in-situ oxidation-reduction. In vitro experimental results demonstrated that the Se@Me@MnO₂ nanozyme exhibits multiple enzyme activities to scavenge ROS, including catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD). Mechanism researches illustrated that the Se core possesses GPx-like catalytic activity, the Me and the MnO₂ possess both the SOD-like and the CAT-like activities. What’s more, due to the stable unpaired electrons existing in the nanozyme, the Se, Me and MnO₂ provide synergistic and fast electron transfer effect to achieve the quickly scavenging of hydrogen peroxide, hydroxyl radical, and superoxide anion. Further in vivo experimental results showed that this biocompatible nanozyme exhibits cytoprotective effects by resisting ROS-mediated damage, thereby alleviating the inflammation. This multienzyme mimetics is believed to be an excellent ROS scavenger and have a good potential in clinical therapy for ROS-related diseases.

A novel egg-like nanosphere was designed as a long-lived catalyst and is described as Fe₃O₄@nSiO₂-NH₂-Fe₂O₃·xBi₂O₃@mSiO₂. The catalyst was prepared using a modified Stöber method with template-free surface-protected etching. The catalyst particle consists of a magnetic Fe₃O₄ core as the "yolk", an inner silica shell bearing active Fe₂O₃·xBi₂O₃ species as the "egg white", and outer mesoporous silica as the "egg shell". It exhibits an excellent performance in the catalytic reduction of nitro aromatics to corresponding anilines in a fixed-bed continuous-flow reactor. The reaction could be performed at 80 ℃ and could reach complete conversion in less than 1 min with only a 7% excess of hydrazine hydrate. The catalyst bed could be easily shifted between different substrates without cross-contamination because of the uniformity of the catalyst particles. This catalyst exhibited very good stability in the continuous-flow protocol. In the long-term reduction of p-nitrophenol with 0.5 mmol·min^-1 productivity, it worked for more than 1, 500 cycles without any catalytic activity loss.