Synthesis And Functionalization Of Superparamagnetic Fe₃O₄Nanoparticles For Protein Separation

Iron oxide superparamagnetic nanoparticles, including magnetite (Fe3O4) andmaghemite (γ-Fe2O3), have been intensively investigated due to their potentialapplications in biomedical, diagnosis, magnetic fluids, catalysis, data storage, andenvironmental remediation. Synthesis and Functionalization of superparamagneticiron oxide nanoparticles have now become a hot topic in scientific research. Amongthe methods of sythesizing magnetic nanoparticles，thermal decomposition of organicprecursors seems to exhibit advantages in preparing high-quality and monodispersedmagnetite nanoparticles. Here, we use a modified thermal decomposition method toprepare monodispersed Fe3O4nanoparticles with uniform size and shape, and modifythe surface with dopamine to prepare water-dispersible nanoparticles, and thenexplore the application in the field of protein separation． The specific studies are asfollows:(1) we report the one-pot reaction between benzyl alcohol and iron(III)acetylacetonate for the formation of superparamagnetic Fe3O4nanoparticles withuniform size and high-purity. As-prepared Fe3O4nanoparticles have excellentmonodispersity in organic solvent (DMSO) and superparamagnetic property. The newapproach is a simple,“green”, one-pot procedure using commercially availableprecursors and benzyl alcohol as solvent and ligand at the same time. It is the specialadvantage of this technique that the particles could be easily coated after synthesiswith minimal amounts of ligands for functionalization.(2) Fe3O4nanoparticles is functionalized with dopamine to prepared waterdispersible Fe3O4nanoparticles (MNP-DA). Characterization of MNP-DAnanoparticles by using TEM, DLS, water-solubility test and stability test show thatMNP-DA nanoparticles are readily dispersed in water and much more stable than the as-prepared MNPs in water. MNP-DA nanoparticles are stable for more than80daysin water without any observed aggregation. Comparing to other methods preparingwater-dispersible nanoparticles, this approach is environmental friendly, safe and canproceed under mild conditions. What’s more, the properties that dopamine modifiedsurfaces are reactive towards molecules bearing amino-or thiol-group in a facile andefcient way enabled MNP-DA ready for direct bio-functionalization and proteinseparation (such as BSA separation).(3) The application of superparamagnetic Fe3O4nanoparticles for proteinseparation. MNP-DA can react with protein in alkaline solution for separating proteinfrom other molecules without amino-or thiol-group. To demonstrate this statement,we synthesize BSA-Au fluorescent nanostructure using a simple and “green” routeand mixed it with a fluorescein disodium salt. When MNP-DA nanoparticles areincubated with a mixture solution containing both BSA-Au and fluorescein disodiumsalt and then separated from the mixture using a magnet the supernatant exhibitedgreen emission. This indicate the efciently selective removal of BSA-Au from themixture solution, which initially showed a yellow emission.(4) Functionalization of MNP-DA for protein separation reversibly. Based on thefact that molecules containing amine or thiol group can specically attach to MNP-DA,one-step functionalization of MNP-DA nanoparticles. MNP-DA nanoparticles arefunctionalized with Na,Na-bis(carbox-ymethyl)-L-lysine hydrate (NTA) to preparefunctional MNP-NTA nanoparticles，and after the chelation of MNP-NTA with Ni2+,MNP-NTA(Ni2+) separate F-His-proteins from the solution, and F-His-proteinsimmobilized on the surface of iron oxide nanoparticles can be released reversibly withimidazole. We demonstrate this process with fluorescent change of F-His-proteinssolution.