Study On The Acting Regulation Of Iron Oxide Nanozyme Activity By Magnetic Field Stimulation

Nanozymes have attracted widespread attention in the past ten years due to their advantages such as good stability,low cost,easy mass production and adjustable catalytic activity.The catalytic activity of nanozymes is extremely important for its application in the field of biomedicine.Magnetic field is an exogenous stimulus that has no tissue penetration depth limitation and has excellent safety.It has unique advantages in the regulation of enzyme activity,but the effect of magnetic stimulation on fine-tuning the nanozyme activities remains unclear.To this end,a series of iron oxide nanozymes with different specific absorption rate(SAR)have been constructed in this paper.The reaction velocities of the peroxidase activities under in situ alternating magnetic field treatments were determined in real-time and the underlying mechanism was explored.This work is expected to provide theoretical support for the design of magnetically responsive nanozymes to enhance their performance in tumor treatment.The specific content and results are as follows:(1)Three kinds of iron oxide nanoparticles of 6 nm,13 nm and 20 nm diameter were successfully prepared by high temperature thermal decomposition method using iron oxyhydroxide as the precursor,named SPIO-6,SPIO-13 a and SPIO-20 respectively.Through TEM,XRD,VSM,FTIR,DLS and other characterizations,the particles are shown to have uniform morphology,narrow particle size distribution,and saturation magnetization of 22.7,37.1,and 53.5 emu/g,respectively.When there is no external magnetic field,the catalytic activity of smaller particles is higher;however,with the application of an external magnetic field,the higher the magneto-thermal conversion efficiency of the particles,the greater increase in its nanozyme activity.(2)Another 13 nm iron oxide nanoparticle was prepared by the high-temperature thermal decomposition method with the iron oleate complex precursor,named SPIO-13 b.The characterization showed that the sizes of SPIO-13 b and SPIO-13 a are the same.However,the saturation magnetization of SPIO-13 b is 30.6 emu/g,which is smaller than SPIO-13 a.When no magnetic field is applied,the activities of SPIO-13 a and SPIO-13 b are similar.When different field strengths are applied,the increase of SPIO-13 a activity is significantly greater than that of SPIO-13 b.It is proved that the fundamental reason for activity enhancement by magnetic stimulation is due to the nanothermal effect.With no increase in solution temperature,the nanozyme activity is enhanced upon field exposure and the magnitude of activity enhancement depends on the magnetothermal conversion efficiency of the particles themselves.(3)The 70 nm ferrimagnetic vortex iron oxide(FVIO)was synthesized by hydrothermal method,and it was shown to have a unique vortex magnetic domain and a high saturation magnetization of 68 emu/g,and it has a good magnetocaloric conversion efficiency with the SAR 2100 W/g.In addition,magnetic stimulation can significantly enhance its enzyme activity,with an increase of 39.2% at 350 Oe.It was once again verified that the magnitude of the activity enhancement depends on the magneto-thermal conversion efficiency of the particles themselves.