Study Of Graphene Oxide And Au/Ag Nanoparticles Applied In SPR Sensor

Surface plasmon resonance (SPR) biosensors have become an indispensabletool for studying biomolecular interactions in pharmaceutical and biomedical researchover the past decades. One of the main drawbacks that impede further development ofSPR applications is the lack of sufficient sensitivity to reliably detect small changes inrefractive index caused by compounds in low concentration at the sensing surface.Several novel SPR biosensor structures and approaches are reported to address suchlimitations, such as gold nanoparticles, magnetic nanoparticles, carbon nanotubes,ZnO–Au nanocomposites, and functionalized parylene film. Specifically, plentifulmethods have focused on developing substrate based on noble metal nanoparticlessuch as gold and silver. Systems based on noble metal nanoparticles can be easilyprepared and have fairly high enhancement factor because of the strong plasmoniccoupling between noble metal nanoparticles and gold or silver substrates, whichinduces electric field enhancement and leads to high detection sensitivity.Nanoparticles with sharp tips (nanotriangles, bipyramids) exhibit especially highrefractive index sensitivities. Three sharp vertices or tips of triangular nanoplatescontribute significantly to their optical and electronic properties. These tips act as‘‘hot spots’’ and are very sensitive to bulk and local dielectric changes. In the presentwork, TSNPs（triangular silver nanoplates）modified with MPA (3-Mercaptopropinicacid) were mixed with chitosan and cross-linked by glutaraldehyde. The performanceof SPR biosensor was improved by spin-coating the SPR biochip withTSNPs/chitosan composite. Differing from employing common sphericalnanoparticles to improve the performance of SPR biosensor, triangular silvernanostructure was used to induce electromagnetic coupling and amplify the response of the binding of antigen to antibody. The experiment results show that the sensitivityof SPR biosensor based on TSNPs/chitosan composite was significantly enhanced andthe immobilization procedure of antibody was simplified.Graphene oxide (GO) is a strongly oxygenated, highly hydrophilic layeredmaterial. Abundant oxygen-containing functional groups on its basal planes and edgesenable GO to interact with varieties of biomolecules through covalent, noncovalent orelectrostatic interactions. In addition, its effectiveness in quenching fluorescenceaffords advantages over alternative carbon materials such as nanodiamonds, andcarbon nanotubes that have been investigated for biosensing. Considering its largespecific surface area, long-term stability, friendly biocompatibility and exceptionalfluorescence-quenching ability, GO-based sensors have been successfully applied tothe detection of ss-DNA, metal ions, living cells and Salmonella typhi. Comparedwith spherical Au nanoparticles, Au nanorods (AuNRs) exhibit two plasmonresonance wavelengths defined as transverse and longitudinal mode. The longitudinalband of AuNRs has been found to be very sensitive to changes in the localenvironment. Here we report a novel SPR biosensor using GO sheets decorated withAuNR-antibody conjugates substrate (AuNR: Au nanorods). AuNR-antibodyconjugates were immobilized on the GO sheets by a carbodiimide-assisted amidationreaction. The high loading capacity and good biocompatibility of GO together withremarkable optical property of AuNRs are beneficial to antibody immobilization andsensitivity enhancement of detection. It is anticipated that this sensor can be used fordetecting various proteins by decorating GO sheets with selected AuNR-antibodyconjugates, which makes the new sensor capable of detecting a variety of proteins andprovides a promising potential for manufacturing other sensitive biosensors. After that,a novel GO-based SPR biosensor using AuBPs (Au bipyramids) as sensitivityenhancers for the determination of bovine IgM is proposed. Consequently, theas-prepared GO sheets function as promising support for antibody and GO-based SPRbiosensor using AuBPs as enhancers has the highest sensitivity among the four typesof biosensors.Recently, GO has been used extensively as a substrate to fabricate nanohybrid materials. It is expected that the nanoparticles anchored on the sheet potentiallyexhibit novel catalytic, magnetic, and optoelectronic properties. A variety ofnanoparticles including Pb, Pt, Au, TiO2, and Fe3O4have been hosted on the surfaceof GO. In this paper, the Au-GO composite was synthesized and applied in the SPRbiosensor as solid support for the direct immobilization of goat anti-rabbit IgG. Theas-prepared composite assembles directly onto the Au film surface of SPR sensor.Meanwhile, SPA specifically recognizes and binds the Fc portion of antibodies,contributing to highly oriented antibody immobilization on the chip surface withoutany antibody modification. Experimental results show that SPA modified Au GOcomposite can be successfully used for the signal amplification of immunosensor,thereby improving the sensitivity and obviating the need of chemical modification ofthe antibody.