Preparation Of Fe₃O₄/O-Carboxylated Chitosan Magnetic Nanoassembles And Their Adsorption And Desorption Behavior Of Bovine Serum Albumin

Fe3O4 nanoparticles(Fe3O4 MNPs)with small size have specific properties of superparamagnetism,high spin-spin relaxation rate,easy surface modification and controllable size.They are widely applied in magnetic resonance imaging,thermal therapy,drug targeted delivery and biological separation.However,the intensity of magnetization of single Fe3O4 MNP is low to cause a weak response to external magnetic field and the load capacity,which limits its application in the fields of drug targeted delivery and biological separation.Self-assembly of multiple Fe3O4 MNPs to form magnetic nanoassemblies(MNAs)not only maintains the inherent superparamagnetism of single Fe3O4 MNPs,but also all Fe3O4 MNPs constituting MNAs can form a synergistic and rapid response to changes in applied magnetic fields.In addition,there are a large number of pores between Fe3O4 MNPs,which can give MNAs excellent load capacity.However,most of the current techniques based on self-assembly for the preparation of MNAs must be carried out in relatively low concentration,otherwise the colloidal stability and particle morphology of MNAs are easily lost.The inverse miniemulsion is a heterogeneous reaction system in which the polar droplets are the dispersed phase and the non-polar solvent is the continuous phase.The technique can prepare various hydrophilic nano-materials at a higher concentration of the dispersed phase.In this paper,Fe3O4/O-carboxylated chitosan MNAs(Fe3O4/OCMC MNAs)with high magnetic responsiveness and superparamagnetism were prepared by self-assembly of Fe3O4 MNPs in dispersed phase droplets of the inverse miniemulsion system and Schiff base reaction.Firstly,OCMC-stabilized Fe3O4 MNPs(OCMC-Fe3O4 MNPs)were prepared by co-precipitation method using OCMC as a colloidal stabilizer.Then OCMC-Fe3O4 MNPs aqueous dispersion was prepared as droplet phase of inverse miniemulsion.Fe3O4/OCMC MNAs with good dispersibility and structural stability in both the inverse phase system and the water system were prepared by the the Schiff base reaction of cross-linking agent glutaraldehyde(GA)and OCMC.The prepared Fe3O4/OCMC MNAs have superparamagnetic properties,strong magnetic responsiveness and porous structure,and have potential application value in drug loading and delivery,separation of proteins and other biological macromolecules.The feature,microstructure,composition and magnetic properties of Fe3O4/OCMC MNAs were characterized by transmission electron microscopy,Fourier transform infrared spectroscopy,X-ray diffraction,thermogravimetry and magnetic testing.The effects of the amount of emulsifier Span 80 and cross-linking agent GA on the colloidal stability of the synthetic system and the morphology of Fe3O4/OCMC MNAs were investigated.It was found that as the amount of Span 80 increased,the colloidal stability of the system increased and the morphology gradually became regular.By measuring the amount of residual amino groups,the Schiff base reaction between GA and OCMC was followed.It was found that as the amount of GA increased,the final amino group content continued to decrease,and the degree of crosslinking increased.Although the degree of crosslinking of OCMC has little effect on the morphology of Fe3O4/OCMC MNAs in inverse miniemulsions,it has an effect on the morphology of Fe3O4/OCMC MNAs in aqueous dispersions.Considering that the subsequent application of Fe3O4/OCMC MNAs involves water environment,the water dispersibility of Fe3O4/OCMC MNAs was systematically studied.The water dispersion conditions of Fe3O4/OCMC MNAs were optimized.The effects of Span 80 and GA on the water dispersibility of Fe3O4/OCMC MNAs and their morphology in water were systematically studied.The optimal spans of Span 80 and GA were obtained.The stability of the imine bond formed by Schiff base reaction under different pH conditions was investigated.It was found that under acidic conditions,the imine will be partially degraded,which will increase the swelling ability of Fe3O4/OCMC MNAs by water,but still have a certain structure.Stability,no disintegration of MNAs;under neutral and alkaline conditions,Fe3O4/OCMC MNAs have high structural stability because the stability imine bond is excellent.Finally,bovine serum albumin(BSA)was used as the model protein,and Fe3O4/OCMC MNAs was used as the adsorbent.The effects of adsorbent dosage,pH value and adsorption temperature on the adsorption and desorption behavior of protein were studied.The results showed that with the increase of Fe3O4/OCMC MNAs,the equilibrium adsorption capacity shows a gradual decline.With the increase of pH value,the negative charge of Fe3O4/OCMC MNAs and BSA surface increases gradually,causing the electrostatic repulsion increases,resulting in equilibrium adsorption capacity.As the adsorption temperature increased,the equilibrium adsorption capacity first increased and then decreased,the adsorption of BSA by Fe3O4/OCMC MNAs accorded with the Langmuir equation and pseudo-secondary kinetics,the desorption efficiency of the six cycles was above 80%.And the desorbed BSA still had better activity with desorption of six times.The above results indicated that Fe3O4/OCMC MNAs have pH-dependent reversible adsorption-desorption behavior and strong adsorption capacity for proteins,and have important potential applications in the field of protein separation.The research in this thesis shows that the structure and stability of NAs can be effectively controlled by constructing cross-linking between NPs in the dispersed phase droplets of the inverse miniemulsion system,and the structure and size of NAs in inverse phase system and water can be regulated.The research methods involved in this thesis have important reference significance for the preparation and application of polymer/inorganic particles NAs with high inorganic content and structural stability.