Synthesis Of Magnetic Nanocomposites And Their Applications In Electrochemical Sensing

Magnetite nanoparticles have long been one of the most promising materials because of their good biocompatibility, strong superparamagnetic property, low toxicity and easy preparation and great potential for various biomedical applications, such as magnetic data storage, NMR imaging, targeted drug delivery, and biomolecule separation. Various magnetic nanocomposites have been intensively investigated because of their hybrid properties of the involved magnetic nanoparticles and other materials. In this dissertation, various magnetic nanocomposites with excellent properties have been designed and synthesized, such as ferrocene-modified magnetic nanoparticles, core-shell metal or metal oxide coated Fe3O4 nanoparticles, graphene/Fe3O4 composite, Au-polydopamine-Fe3O4-graphene nanocomposite, and protein-Au-polydopamine-Fe3O4 magnetic bionanoparticles and applied to construct a series of novel electrochemical sensing. The details are given as follows:1. IntrodutionIn this section, the characteristics, synthesis methods, and modification of the magnetic nanomaterials and their composites were introduced, and their applications in biochemistry and medicine were summarized. Furthermore, we have described the electrochemical biosensor and summarized the applications of magnetic materials in electrochemistry sensing. At last, the works and innovations of this dissertation were presented.2. The preparation of ferrocene-modified Fe3O4@SiO2 magnetic nanoparticles and their applications for electrochemical biosensorA novel amperometric glucose biosensor was developed by entrapping glucose oxidase in chitosan composite doped with ferrocene monocarboxylic acid-modified magnetic core-shell Fe3O4@SiO2 nanoparticles (FMC-AFSNPs). It is shown that the obtained magnetic bio-nanoparticles attached to the surface of a carbon paste electrode with the employment of a permanent magnet showed excellent electrochemical characteristics and at the same time acted as mediator to transfer electrons between the enzyme and the electrode. Under optimal conditions, this biosensor was able to detect glucose in the linear range from 1.0×10-5～4.0×10-3 M with a detection limit of 3.2μM (S/N=3). This immobilization approach effectively improved the stability of the electron transfer mediator and is promising for construction of biosensor and bioelectronic devices.3. The construction of core-shell magnetic nanoparticles/heme protein nano-functional interfaces and their applicationsA simple approach for the immobilization of heme proteins using core-shell magnetic nanoparticles (Fe3O4@Au, Fe3O4@ZrO2 and Fe3O4@Al2O3) as the building block has been developed, and the direct electron transfer between the immobilized proteins and electrode was studied. The bifunctional core-shell magnetic nanoparticles were initially deposited on the electrode surface by applying a constant magnetic field, and then heme proteins were immobilized on the core-shell magnetic nanoparticles surface via interaction between the shell and the protein. Transmission electron microscope, UV-vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry were carried out to characterize the morphology, structure, and electrochemistry of the nanocomposite and the biofilm. The modified electrode based on this core-shell magnetic nanoparticles/heme proteins films well retained the native structure of the immobilized proteins and displayed good electrocatalytic activity to the reduction of H2O2. The proposed method simplified the immobilization methodology of proteins and showed potential application for construction of third-generation biosensors and other bio-magnetic induction devices.4. The synthesis of Fe3O4/graphene nanocomposite and its application in electrochemical sensingA novel electrochemical sensing platform based on graphene supported Fe3O4 nanoparticles (Fe3O4/rGO) composite was constructed for the detection of hydrogen peroxide (H2O2). The Fe3O4/rGO composite was prepared by one-step in situ high-temperature decomposition of the precursor iron (Ⅲ) acetylacetonate on graphene oxide sheets in polyol solution. The morphologies and characteristics of the as-prepared Fe3O4/rGO composite were investigated by using transmission electron microscopy, X-ray diffraction, UV-vis spectroscopy, Fourier transform infrared spectra and electrochemical techniques, respectively. With the advantages of the magnetism and the intrinsic peroxidase-like activity of Fe3O4 nanoparticles, the composite film could be easily fabricated in the present of external magnetic field and shows excellent electrocatalytic activity towards the reduction of H2O2. In addition, the large surface area and high electrical conductivity of graphene dramatically increased the loading capability of Fe3O4 nanoparticles and enhanced the conductivity of the composite. Together with the electrocatalytic activity of the graphene towards H2O2, the Fe3O4/rGO composite-modified electrode had a better synergistic electrocatalytic effect on the reduction of H2O2 than did Fe3O4 or graphene-modified electrode. At physiological condition, the constructed sensor showed a linear range for the detection of H2O2 from 2.0 to 983μM with a low detection limit of 0.66μM (S/N=3) and exhibited high selectivity, excellent stability and reproducibility.5. A label-free amperometric immunosensor based on biocompatible Au-polydopamine-Fe3O4-graphene nanocompositeA novel and facile biomolecule immobilization strategy based on Au-polydopamine-Fe3O4-graphene oxide (Au-PDA-Fe3O4-GO) nanocomposite was used to develop a highly sensitive amperometric immunosensor. The morphologies and characteristics of the as-prepared Au-PDA-Fe3O4-GO nanocomposite were investigated by using transmission electron microscopy, powder X-ray diffraction, energy dispersive X-ray and electrochemical techniques, respectively. The characteristics of the modified electrode at different stages of modification were studied by cyclic voltammetry and electrochemical impedance spectroscopy. In addition, the performances of the resulting immunosensor were studied by differential pulse voltammetric. The as-prepared Au-PDA-Fe3O4-GO nanocomposite not only provided a favorable microenvironment to maintain the activity of the immobilized HBsAb, but also increased the loading capacity of the HBsAb due to the two-dimensional structure of the graphene, and the present of graphene and Au nanoparticles enhanced the conductivity and charge-transport properties of the composite. In addition, due to the redox characteristic of the Fe3O4 nanoparticles, the constructed immunosensor could realize the electrochemical detection of HBsAg without using other electron mediator. The present immunosensor exhibited a wide linear range from 0.1～180.0 ng ml/-1 with a low detection limit of 0.033 ng-mL-1 at signal to noise ratio of 3. Moreover, the studied biosensor exhibited high sensitivity, good reproducibility and long-term stability. The prepared immunosensor exhibited high selectivity, low detection limit, long-term stability and good reproducibility.6. The synthesis of protein-polydopamine-Au-Fe3O4 nanocomposites and their application in electrochemical biosensorA novel protein-Au-polydopamine-Fe3O4 magnetic polymeric bionanocoparticles (protein-Au-PDA-Fe3O4 MPBNPs) with proteins entrapped at high load/activity for direct electrochemistry was designed and prepared by a one-pot in situ chemical synthesis. As representative materials here, DA as a reductant and a monomer, proteins including hemoglobin (Hb), myoglobin (Mb), horseradish peroxidase (HRP), and glucose oxidase (GOx) as the model proteins/enzyme, Fe3O4 NPs as model magnetic nanomaterial and the core of the MPBNPs, and HAuCl4 as an oxidant to trigger DA polymerization and the source of the Au nanoparticles, were simply mixed to yield protein-Au-PDA-Fe3O4 MPBNPs. Scanning electron microscope, energy dispersive X-ray, UV-vis spectroscopy, and electrochemical methods were used to characterize the protein-Au-PDA-Fe3O4 MPBNPs. Results demonstrated that the resultant protein-Au-PDA-Fe3O4 MPBNPs not only have the magnetism of Fe3O4 NPs which makes them easily manipulated by an external magnetic field, but also have the excellent biocompatibility of the functional shell which can maintain the native structure of the entrapped proteins and facilitate the direct electrochemistry of the heme proteins. Based on the direct electron transfer of the immobilized proteins, the protein-Au-PDA-FesO4 MPBNPs-modified electrode exhibited excellent catalytic performance for H2O2.