Study Of Nanoparticles Applied In Improving The Performance Of Surface Plasmon Resonance Sensor

In 1983, the first surface plasmon resonance (SPR) sensor was developed. As an easy, convenient and reliable biosensor, the SPR biosensor can be applied in measuring kinetic constant, binding specificity of individual biomolecules and detecting the concentration of the target. Nowadays, the biosensors based on surface plasmon resonance have become more and more important in studying the determination of interactions between biological molecules, including proteins detection, immunoregulation, gene regulation and signal transduction.Compared with other biosensor techniques, SPR spectroscopy has many advantages, such as real-time, small sample volume, label-free and non-destructive detection. However, the SPR biosensor now limits to scientific research and laboratories research and there is no large-scale industrial application. To overcome this limit, SPR biosensor must possess these characteristics, including rapid and convenient detection, high sensitivity and stable performance. The studies of sensitivity enhancement of SPR biosensor have also been developed. The works include the improved SPR instrument and improved research system. In this paper, the theory of SPR biosensors, its applications and the recent progress are introduced. The wavelength modulation SPR sensors installed in our lab are used to detect antigens. And a series of work were conducted to improve the performance of SPR biosensor, especially the application on nanoparticles.Au nanoparticles have especial virtues, such as ease of preparation, large dielectric constant and biocompatibility. More important, the coupling of local surface plasmon of AuNP with the propagating plasmon of the Au film could benefit to enhance sensitivity of biosensor. As a result, it has been used widely to study the binding of protein to protein in SPR biosensor. The titania sol-gel membrane is a kind of three-dimensionally porous network, which could offer a waterish microenvironment for biomolecule. A novel SPR biosensor was constructed for the determination of human IgG by trapping colloidal Au nanoparticle (AuNP) and AuNP coupled with rabbit anti-human IgG (anti-IgG) in the different layers of titania sol-gel membrane. At first, thin titania membrane was prepared by vapor deposition technique to avoid direct deposition of AuNP to the Au film. Then the colloidal Au nanoparticle was immobilized in the second layer of titania membrane to enhance the sensitivity of SPR biosensor. Finally, the AuNP coupled with anti-IgG was encapsulated in the third layer of titania membrane. The AuNP immobilized in the third layer of titania membrane could offer a biocompatible microenvironment which is favorable for biomolecule to retain bioactivity. And the analyte is able to diffuse toward the porous network to bind to the immobilized biomolecule. As a result, the sensitivity of the SPR biosensor was enhanced and long-term bioactivity of biomolecule was obtained.In recent years, core/shell Fe₃O₄/Au nanocomposite has attracted considerable technological interest. This material, owning exceptional optical properties and magetic property, is easy to separation, enrichment and immobilization. In conclusion, the Fe₃O₄/Au nanocomposite combines the advantages of Fe₃O₄ and Au nanoparticle and is one of excellent candidates as carrier for proteins immobilization. At first, the Fe₃O₄/Au nanocomposite coupled with rabbit anti-human IgG (anti-IgG) by electrostatic adherence. Then the conjugate was trapped on the Au film by magnetic force, the Fe₃O₄/Au/anti-IgG sensing membrane was prepared. The human IgG can be detected. As there is not a covalent link between the membrane and Au film, this novel method simplifies the immobilization of the antibody and the regeneration of sensing membrane. In addition, the application of Au nanoparticle enhances the sensitivity of biosensor.The proteins can couple with Fe₃O₄/Au nanocomposites through electrostatic adherence or chemical bond. The method with electrostatic adherence is convenient but much weaker compared with the chemical bond. As a result, the amount of antibodies immobilized on the nanocomposite by electrostatic adherence is much less than that immobilized by chemical bond, which is not benefit for the improvement of sensitivity. Due to the carboxylic acid and sulfhydryl in 3-Mercaptopropionic acid (MPA), it can be used to connect anti-human IgM and Fe₃O₄/Au nanocomposites. The deposition of Au shell modified with MPA on Fe₃O₄ nanoparticles through a simple, one-step procedure was reported. And the core/shell Fe₃O₄/Au nanocomposites modified with MPA were applied in the surface plasmon resonance (SPR) biosensor as the solid support for the goat anti-human IgM. Meanwhile, the conjugates of Fe₃O₄/Au nanocomposites with antibody could be immobilized on the surface of SPR biosensor by a magnetic pillar. In addition, the thickness of Au shell deposited on the Fe₃O₄ nanoparticles decreases as the amount of MPA increases. So the different sizes of Fe₃O₄/Au nanocomposites were obtained successfully with the different amount of MPA in the solution. The effect of Fe₃O₄/Au nanocomposites with different sizes on the sensitivity of SPR biosensor was also explored. As a result, the SPR biosensor exhibits high sensitivity and the increasing nanocomposites size is favor for the sensitivity enhancement of SPR biosensor.