Liposome-Boosted Peroxidase-Mimicking Nanozymes Breaking the pH Limit

Peroxidase-mimicking nanozymes such as Fe3O4 nanoparticles are promising substitutes for natural enzymes like horseradish peroxidase. However, most such nanozymes work efficiently only in acidic conditions. In this work, the influence of various liposomes on nanozyme activity was studied. By introducing negatively charged liposomes, peroxidase-mimicking nanozymes achieved oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in neutral and even alkaline conditions, although the activity towards anionic 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) was inhibited. The Fe3O4 nanoparticles adsorbed on the liposomes without disrupting membrane integrity as confirmed by fluorescence quenching, dye leakage assays, and cryo-electron microscopy. Stabilization of the blue-colored oxidized products of TMB by electrostatic interactions was believed to be the reason for the enhanced activity. This work has introduced lipids to nanozyme research, and it also has practically important applications for using nanozymes at neutral pH, such as the detection of hydrogen peroxide and glucose.