| Since the first commercially available surface plasmon resonance (SPR) sensorhas been introduced, various SPR sensors have been unprecedented development andquickly applied to the areas of biotechnology, medical diagnostic, environmentalprotection and food safety. Compared with other biosensor techniques, SPR biosensorhas many advantages. The SPR biosensor can provides a rapid, label-free and highlysensitive assay, which has been widely investigated as a bioanalytical tool to analyzebiomolecules such as proteins, cells, hormone, oligonucleotides and antigens.SPR is a surface-sensitive analytical technique based on the ability to detectchanges in the refractive index. While, conventional SPR is unable to measureextremely small changes in refractive index, which hinders its application onultrasensitive detection. To overcome this drawback, several approaches have beenapplied by altering external structure. In this paper, the theory, application and recentprogress of SPR biosensor are introduced. The wavelength modulation SPR sensorsinstalled in our lab are outlined, which are used to detect antigens. And somenanoparticles are introduced to improve the performance of SPR biosensor.Metal nanoparticles, especially Au and Ag nanoparticles, have been used to theSPR sensors because of their unique optical properties. The electronic couplingbetween the localized surface plasmon of the nanoparticles and the propagatingplasmon wave from the surface of the Au film leads to the enhanced shifts of theresonant wavelength. Au nanoparticle has been used widely in immunoassays owingto its excellent properties, such as easy reductive preparation, water-solubility, highchemical stability and significant biocompatibility. However, Ag nanoparticle shows better sensitivity, which could be used to enhance the sensitivity of the biosensor.Compared with Au nanoparticles, bare Ag nanoparticles were unstable. Therefore, toaddress these drawbacks, alloy nanocomposites have gained significant interest.Au/Ag alloy nanocomposites combine the advantages of Au and Ag nanoparticles,which lead to their promising application in the fields of optical devices, biomedicalresearch and electronics. In this paper, Au/Ag alloy nanocomposites were synthesizedand applied in the SPR biosensor to amplify SPR response signal.1,6-hexanedithiol(HDT), a disulfide compound, was used to connect the Au film and the Au/Ag alloynanocomposites. Then,3-mercaptopropionicacid (MPA) was used to connect theAu/Ag alloy nanocomposites and the biological components. After the carboxyl groupof MPA was activated, antibody could bind to the alloy nanocomposites steadily.When the biosensor based on Au/Ag alloy nanocomposites was used to determinehuman IgG, the range of concentrations for human IgG that could be determined is0.15-40.00μg mL-1. The limit of quantification for human IgG obtained by thebiosensor based on Au/Ag alloy nanocomposites was about eight times lower thanthat obtained by the biosensor based on Au film alone and about two times lower thanthat obtained by the biosensor based on Au nanoparticles. Therefore, the biosensorbased on Au/Ag alloy nanocomposites shows high sensitive and is suitable fordetection of human IgG.Magnetic microbeads have unique magnetic features which are not present inother materials. So they have increasingly been used in the field of bioscience recently.The magnetic nanocomposites can be immobilized on the surface of the sensing filmby a magnetic pillar easily without covalent link between the Au film and theantibody in traditional method of SPR biosensor. However, the application ofmagnetic nanoparticles has been limited due to its inherent properties. Pure magneticnanoparticles are likely to form a large aggregation, easily oxidized or dissolved in anacid medium and have fewer activating group. Therefore, many researchers havefocused on preparation of composite magnetic nanocomposites to obtain novelproperties. Recently, the incorporation of optically active components onto magneticnanoparticles has attracted many attentions. Owing to inner iron oxide core with an outer metallic shell, the nanocomposites can be stabilized more efficiently incorrosive biological conditions and readily functionalized through binding the variousbiological ligands at the nanocomposites surface. Here the Fe3O4/Ag/Aunanocomposites were successfully used in wavelength modulation SPR biosensor todetect dog IgG. The biosensor based on Fe3O4/Ag/Au nanocomposites exhibits aresponse to dog IgG in the concentration range of0.15–40.00μg ml-1and LOQ isabout8times lower than that obtained without nanocomposites modified biosensorfilm. Therefore, this primary study demonstrates that the Fe3O4/Ag/Aunanocomposites were beneficial to the improvement of the SPR sensor performance. |
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