The Application Of Nano Materials To Surface Plasmon Resonance Sensor

In recent years, surface plasmon resonance (SPR) sensors have become more and more important in studying molecular interactions. The most important characteristics of SPR sensor are its versatility and capability in real time monitoring the association or dissociation of biomolecules on the surface of the sensor without the need for fluorescence or labeling of the biomolecules. SPR sensors are especially suitable for the determination of interactions between biological molecules. Great progress has been made in the field of SPR for the determination of antibody, antigen, enzymes, receptors, growth factors, glycoproteins, nucleic acids and drugs.With the development of life science, there is a growing requirement for high sensitive detection technologies in analysis of biological samples. So the studies of sensitivity enhancement of SPR biosensor have also been developed and various measurement formats have been adopted for SPR biosensor. The primary theory and technical characteristics of SPR sensor are introduced. The characteristics of nano materials and the application of some common nanoparticles are introduced. The wavelength modulation SPR sensors installed in our laborory are outlined and the latest developments of nano materials in the application of SPR sensor were summarized.Au and Ag are the ideal candidates as metal films in the visible light region. Compared with Au film. Ag film produces the sharper peak and shows higher sensitivity. The Au film was very stable, strongly adhered to the glass and did not react with the inorganic ions in the reaction system. As a result, Au film can be used as the substrate due to its stability in the SPR biological systems. Silver mirror reaction was used to deposit the Ag film on Au substrate film. In order to avoid Ag film falling off from the Au substrate film,1, 6-hexanedithiol (HDT) was used to modify the Au film, and then thin Ag film was formed on this film by silver mirror reaction. Subsequently,3-mercaptopropionic acid (MPA) was used to connect Ag film with biological components. In this method, Ag film could exist stably between HDT and MPA. When the SPR biosensor based on this Ag/Au film was used to determine human IgG, the range of concentrations for human IgG that could be determined is 0.30-40.00μg mL-1. The lowest concentration (0.30μg mL-1) that could be detected was about 8 times lower than that obtained by the biosensor without modification with Ag film (2.50μg mL-1), which demonstrated that the biosensor based on Ag/Au film could make the resonant wavelength move to longer wavelength following with the sensitivity enhancement of the SPR biosensor.Recently, metal nanoparticles on the surface of semiconductor nanostructures have become a popular research topic because of the improved optical properties of the semiconductor. Au nanoparticle has been used widely in immunoassays owing to its excellent properties. ZnO nanocrystals are synthesized in organic media and unstable in aqueous solution, while biological conjugation usually exists in water solution. In order to satisfy the primary requirement of biological research, the surface of ZnO nanocrystals should be modified. ZnO-Au nanocomposites could be applied in immunoassays for their characteristics such as high solubility in water, biocompatibility and lower toxicity than other semiconductor nanocrystals. The ZnO-Au nanocomposites could provide organic functionality for bioconjugation and then application in SPR biosensor. In order to build a biosensor based on ZnO-Au nanocomposites, it is critical to study the attachment mechanism of the protein onto the ZnO-Au surface, and the interaction between the surface and the biomaterials. The thiol-gold interaction was relatively easy, which was applied to the self-assembly of monolayer (SAM) on Au surface. As 1,6-hexanedithiol (HDT) is a disulfide compound, it could be used to connect Au film and the ZnO-Au nanocomposites. The reactive ZnO surface offers the opportunity for effective bio-ZnO interfaces. First, the ZnO surface could be hydroxylized readily in water. followed by silanization with 3-aminopropyltrimethoxysilane (APTMS). Then the gluteraldehyde was used as the bridge to bind the protein and silanized ZnO. As a result, the immobilization of protein on the surface of the ZnO-Au sensor is achieved. The biosensor based on ZnO-Au nanocomposites exhibits a response to human IgM in the concentration range of 0.30-20.00μg mL-1. And the lowest concentration that could be detected is lower than that based on the Au film. Therefore, the biosensor based on ZnO-Au nanocomposites shows high sensitive and is suitable for the detection of human IgM.In order to enhance the sensitivity of the SPR biosensor, it is important to construct a protein probe modified with ZnO-Au nanocomposites. The ZnO-Au nanocomposites can bind protein by covalent attachment to construct a protein probe. Here 3-Mercaptopropionic acid (MPA) was used to connect the Au nanoparticles in ZnO-Au nanocomposites as the strong, specific interaction between the thiol-gold interactions. After the carboxyl group of MPA was activated, ZnO-Au nanocomposites could be bound to antigen. When the ZnO-Au-antigen interacts with antibody immobilized on the SPR biosensor, the bindings of ZnO-Au-protein-protein lead to change in the refractive index at the sensor surface. The change results in the shifts of resonant wavelength which can be easily measured by SPR biosensor. For comparison, Au-protein probes were also prepared by adding rabbit IgG to Au nanoparticles solution. Under the optimized conditions, the biosensor based on ZnO-Au nanocomposites exhibits a satisfactory response to rabbit IgG in the concentration range of 0.15-20.00μg mL-1. For comparison, the biosensor based on Au film and the biosensor based on Au nanoparticles were also studied for the detection of rabbit IgG. The biosensor based on Au film shows a response to rabbit IgG in the concentration range of 2.50-20.00μg mL-1. And the biosensor based on Au nanoparticles shows a response in the concentration range of 0.30-20.00μg mL-1. The biosensor based on ZnO-Au nanocomposites was therefore found to be the most sensitive one of the three types of biosensor. The lowest concentration of rabbit IgG that can be determine by the proposed biosensor is about 16-fold lower than that obtained with the biosensor based on Au film alone.Recently, magnetic nanoparticles were used as an immobilization matrix and have been increasingly applied to immobilizing proteins, enzymes, and other bioactive agents in analytical biochemistry, medicine, and biotechnology. Pure magnetic nanoparticles are likely to form a large aggregation, have few activating group and are easily oxidized or dissolved in an acid medium. Therefore, a suitable coating on the surface of the pure magnetic nanoparticles is essential to avoid such limitations, meanwhile improves the physicochemical properties of the nanoparticles and maintains the colloidal suspension stability within the biological environment. Core/shell Fe3O4/SiO2 and Fe3O4/Ag/SiO2 nanoparticles were synthesized and applied to the SPR biosensor. The aldehyde group functionalized Fe3O4/SiO2 and Fe3O4/Ag/SiO2 nanoparticles provide organic functionality for bioconjugation. Compared with traditional biosensor immobilized a self-assembled monolayer on the surface of the Au film, silica-coated magnetite nanoparticles have larger surface areas and better compatibilities. So they are ideal immobilization matrixes for biomolecules and beneficial to immobilization of antibody. Furthermore, because Ag nanoparticles could amplify the signal of the SPR biosensor, Fe3O4/Ag nanoparticles were prepared by reducing silver nitrate on the surface of Fe3O4 nanoparticles using the reverse micelle technology to enhance the sensitivity of the SPR biosensor. Then silica was formed on the surface of Fe3O4/Ag nanoparticles by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in the ethanol-ammonia mixture solution. Silica nanoparticles have been effectively applied to the immobilization of various biomolecules and proved to be excellent shell-forming material in the fabrication of biosensors. Fe3O4/Ag/SiO2 nanoparticles have the characteristics of magnetic properties, good compatibilities and can enhance the sensitivity of the biosensor in a certain degree. The core/shell Fe3O4/SiO2 and Fe3O4Ag/SiO2 magnetic nanoparticles could be easily separated from the solution based on their superparamagnetic properties. When the aldehyde group functionalized magnetic nanoparticles were applied in SPR biosensor by a magnetic pillar, the gluteraldehyde was used as the bridge to bind the antibody and the magnetic nanoparticles. The effects of Fe3O4/SiO2 and Fe3O4/Ag/SiO2 nanoparticles on the sensitivity of SPR biosensors were also investigated. As a result. the SPR biosensors based on Fe3O4/SiO2 nanoparticles and Fe3O4/Ag/SiO2 nanoparticles exhibit a response for rabbit IgG in the concentration range of 1.25-20.00μg mL-1 and 0.30-20.00μg mL-1, respectively.