Study On The Environmental Behavior,Toxicity And Underlying Mechanism Of Superparamagnetic Iron Oxide Nanoparticles

Nowadays,nano-materials have been extensively used in the fields of environmental restoration,food processing,wastewater treatment,biomedicine,drug delivery and biosensor.Among many nano-particle compounds,superparamagnetic iron oxide nanoparticles（SPIONs）with anti-spinel structure have been widely studied and applied for their easy synthesis,chemical stability,biocompatibility and superparamagnetism.Especially in the biomedical field,SPIONs has become a highly competitive medical resource.Therefore,SPIONs will inevitably enter the environment and organisms in life cycle,which will have a certain impact on the environment and organisms.Consequently,it is significant to explore the environmental behavior and biological toxicity of SPIONs in the natural environment for the further application of SPIONs.Under this background,this paper synthesized SPIONs and SPIONs-Si O₂ by coating the inorganic material of Si O₂,and learned the effect of different water components on the environmental behavior of SPIONs and SPIONS-Si O₂ and its mechanism.The toxic effects and mechanisms of SPIONs and SPIONs-Si O₂ were explored at molecular and cellular levels with the typical antioxidant enzymes of superoxide dismutase（SOD）and primary mouse hepatocytes as experimental objects.Meanwhile,the effects of Si O₂ coating on SPIONs were explored.The specific research contents and conclusions are as follows:（1）SPIONs and SPIONs-Si O₂ were prepared by microwave-assisted solvothermal method and improved St?ber method respectively.Transmission electron microscopy（TEM）,X-ray diffraction（XRD）,magnetic properties analysis,dynamic light scattering（DLS）analysis andζpotential analysis were carried out to characterize SPIONs and SPIONs-Si O₂.Results show that the obtained SPIONs and SPIONs-Si O₂ samples have high purity and crystallinity,and their crystal structure corresponds to the inverse spinel structure of Fe₃O₄.The samples are approximately spherical with uniform size and regular morphology,the particle sizes of nanocrystals are 16.5nm and 18.9nm,respectively.The samples have high saturation magnetization,which are 64.7emug^-1 and 41.6emug^-1,respectively,indicating that the coating of Si O₂ reduced the magnetic saturation intensity of SPIONs.The coercivity and remanence of the sample are all zero,which indicates that it exhibits good superparamagnetism at room temperature.In addition,the coating of Si O₂obviously increased the hydration diameter of SPIONs,the absolute value of zeta potential and isoelectric point of SPIONs,indicating that the coating of Si O₂ contributes to the electrostatic repulsion,so it is considered that the iron oxide nanoparticles coated with Si O₂have higher colloidal stability.This part of the study is helpful to provide reference for the innovative design of inorganic material coated with SPION.（2）Two kinds of artificial water systems were prepared to simulate the influence of complex factors in natural water on the environmental behavior of SPIONs and SPIONs-Si O₂.DLS,ICP-MS,adsorption isotherm and kinetic analysis were carried out to investigate the environmental behaviors of SPIONs and SPIONs-Si O₂ in different water bodies.Humic acid（HA）,sodium alginate（SA）and bovine serum albumin（BSA）were selected as typical NOM.The interaction and mechanism of SPIONs and SPIONs-Si O₂ with typical NOM were explored through adsorption isotherm,kinetic analysis,isothermal calorimetric titration（ITC）,fourier infrared spectroscopy（FT-IR）analysis and three-dimensional fluorescence analysis.Meanwhile,by comparing SPIONs and SPIONs-Si O₂,the influence of Si O₂ coating on the environmental behavior of SPIONs and its interaction with NOM was explored.Results show that seawater system aggravated the agglomeration and sedimentation of SPIONs and SPIONs-Si O₂,but inhibited the release of iron ion.In addition,the addition of NOM aggravated the agglomeration and sedimentation of the two kinds of SPIONs and reduced the release of iron ions,which was beneficial to the spatial stability of SPIONs and SPIONs-Si O₂.The adsorption of NOM by SPIONs and SPIONs-Si O₂ is consist with Langmuir adsorption model and second-order kinetics,which shows that the three NOM have been adsorbed by homogeneous monolayer on the surfaces of SPIONS and SPIONS-Si O₂ with chemical adsorption.Hydrophobic force is the main driving force in the binding process between NOM and two kinds of iron oxide nanoparticles.SPIONs and SPIONs-Si O₂ are mainly bound to the aromatic skeleton and aldehydes or ketones of NOM,with the participation of hydroxyl and carboxyl groups.But this combination will affect the fluorescence chromophore of HA and BSA,which will lead to fluorescence quenching.In addition,compared with SPIONs-Si O₂,SPIONs has larger degree of agglomeration,sedimentation,iron ion release,adsorption capacity and binding site with NOM,and has stronger fluorescence quenching effect on NOM.This part study is helpful to correctly evaluate the environmental safety of SPIONs and SPIONs-Si O₂,and provide scientific approaches for the behavior and mechanism of SPIONs and SPIONs-Si O₂ in water systems.（3）The toxic effects and mechanisms of SPIONs and SPIONs-Si O₂ were explored at molecular and cellular levels,respectively,with typical antioxidant enzyme SOD and primary mouse hepatocytes as experimental objects.The interaction of SOD with SPIONs and SPIONs-Si O₂ increased the hydration diameter and isoelectric point of nanoparticles and reduced the release of iron ions,indicating that the combination of SOD can improve the colloidal stability of SPIONs.Hydrophobic force is the main driving force of the interaction between SPIONs,SPIONs-Si O₂ and SOD.The interaction with SPIONs and SPIONs-Si O₂ loosened the secondary structure of SOD,resulting in the loosening of protein skeleton,the extension of peptide chain and the decrease ofα-helix content.At the same time,the microenvironment where the endogenous fluorophore Tyr of SOD is located was affected,resulting in the quenching of endogenous fluorescence.Meanwhile,the molecular activity of SOD showed an increased state.Compared with SPIONs,SPIONs-Si O₂ has a more obvious influence on SOD structure and enzyme activity.In addition,the exposure of SPIONs and SPIONs-Si O₂ can induce excessive ROS production in primary mouse hepatocytes,leading to oxidative stress.With the enhancement of exposure concentration,the level of oxidative stress exceeded the self-cleaning ability of cells,which greatly increased the MDA content and reduced the activities of SOD and CAT enzymes and vitality of cells.Compared with SPIONs,SPIONs-Si O₂ had a greater toxic effect on cells,resulting in more ROS and MDA production and lower cellular and intracellular enzyme activities.This part study will help to clarify the toxic effect and mechanism of SPIONs and SPIONs-Si O₂ at molecular and cellular level,and provide reference for the safe application of SPIONs in the field of life medicine.