Layered double hydroxide-based nanozyme for NO-boost multi-enzyme dynamic therapy with tumor specificity

Reduction of intracellular oxidative stress with a copper-incorporated layered double hydroxide

Biocompatible Cu(II)-doped layered double hydroxide (CMA) nanoparticles were developed to combat reactive oxygen species. The 2-dimensional nanozymes showed both superoxide dismutase- and catalase-like activities in chemical assays, while proving as efficient antioxidants in the reduction of intracellular oxidative stress. The results indicate the great promise of CMA in antioxidant therapies.

Formulation of Antioxidant Composites by Controlled Heteroaggregation of Cerium Oxide and Manganese Oxide Nanozymes

Antioxidant composites based on nanozymes [manganese oxide microflakes (MnO2 MFs) and cerium oxide nanoparticles (CeO2 NPs)] were formulated by controlled heteroaggregation. The interparticle attraction via electrostatic forces was systematically tuned with surface functionalization by the poly(diallyldimethyl chloride) (PDADMAC) polyelectrolyte. The PDADMAC-coated MnO2 MFs (PMn) were heteroaggregated with oppositely charged CeO2 NPs to generate the Ce-PMn composite, while the PDADMAC-functionalized CeO2 NPs (PCe) were immobilized onto bare MnO2 MFs, resulting in the Mn-PCe composite. Both the adsorption of PDADMAC and the self-assembly of oppositely charged particles resulted in charge neutralization and charge reversal at appropriately high doses. The interparticle force regimes, the aggregation states, and the physicochemical properties of the relevant dispersions were also highly dependent on the dose of PDADMAC, as well as that of PDADMAC-functionalized metal oxides (PMO) enabling the fine-tuning and control of colloidal stability. The individual enzyme-like activity of either metal oxide was not compromised by PDADMAC adsorption and/or heteroaggregation, leading to the formation of broad-spectrum antioxidant composites exhibiting multiple enzyme-like activities such as superoxide dismutase, oxidase, and peroxidase-type functions. The low cost and ease of preparation, as well as controllable colloidal properties render such composites potential enzyme mimicking agents in various industrial fields, where processable antioxidant systems are needed.

Enhanced peroxidase-like activity of MOF nanozymes by co-catalysis for colorimetric detection of cholesterol

Metal-organic frameworks (MOFs) have been widely used as nanozymes with a great development prospect due to their unique advantages. It is known that the current Fe-based or Cu-based MOF, etc., exhibits the catalytic activity of nanozymes through the Fenton catalytic reaction. And the conversion efficiency of the Fe3+/Fe2+ or Cu2+/Cu+ cycle is key to the catalytic activity. Therefore, we proposed a novel co-catalytic method to promote the reaction rate of the rate-limiting step of Cu2+/Cu+ conversion in the Fenton reaction of Cu2+/H2O2 to enhance the catalytic activity of the nanozymes. As a proof of concept, the MoCu-2MI nanozyme with high catalytic activity was successfully synthesized using Mo-doped Cu-2MI (2-methylimidazole). By using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, MoCu-2MI exhibited higher peroxidase-like activity than pure Cu-2MI. Then, it was confirmed that the newly introduced Mo played a crucial co-catalytic role by characterizing the possible catalytic mechanism. Specifically, Mo acted as a co-catalyst to accelerate the electron transfer in the system, and then promote the Cu2+/Cu+ cycle in the Cu-Fenton reaction, which was conducive to accelerating the production of a large number of reactive oxygen species (ROS) from H2O2, and finally improve the activity. Ultimately, a biosensor platform combined with MoCu-2MI and cholesterol oxidase realized the one-step colorimetric detection of cholesterol in the range of 2-140 μM with the detection limit as low as 1.2 μM. This study provides a new strategy for regulating the activity of MOF nanozymes.