Synthesis And Application Of Nano-materials In Surface Plasmon Resonance Biosensor

The biosensor is a new technology derived from biology, chemistry, physics,electronics and other disciplines. In recent decades, the biosensor has been developed veryrapidly and got great attention due to its quick analysis, high selectivity and sensitivity,on-line continuous monitoring and many other advantages. The biosensor uses biologicalcomponents as the sensing elements for measuring the biological materials, and is verysensitive to biological materials by changing its concentration into an electrical signal fordetection. The biosensor is widely used in biochemical analysis, environmental monitoring,food industry, clinical examination, military medicine and other fields. There are manykinds of biosensors. The most common biosensors are the optical and electrochemicalbiosensor. Most biosensors require the sample to be labeled before detection, such asenzyme labels, fluorescent labels. The labeling process is not only complicated, but alsointerferes with the nature of the original system and affect the biological activity of themolecule. Surface plasmon resonance (SPR) biosensor is a typical optical biosensor andshows many advantages, such as label-free, real-time monitoring the biomolecular bindingreaction. SPR is considered as one of the most important tools to study biomolecularinteractions, which provides highly accurate experimental results. In this study,nano-materials were used in SPR biosensor and electrochemical biosensor to improve theperformance and enhance the sensitivity. The detection principle and characteristics of SPRbiosensor were introduced. The wavelength modulation SPR biosensor installed in our labwas outlined and the latest developments of nano-materials in the biosensor weresummarized. The Fe3O4-AuNR nanocomposites were produced by means of a seeded growth method,in which the Fe3O4nanoparticles were used as seeds. The nanocomposites were used as thesubstrate in the SPR biosensor to detect goat IgM. The nanocomposites exhibit bothmagnetic property and exceptional optical property, which are beneficial to the antibodyimmobilization and the sensitivity of detection. The sensing membrane can be regeneratedeasily and the experimental procedure is simplified. Compared with traditional biosensorimmobilized with a self-assembled monolayer on the surface of Au film, Fe3O4-AuNRnanocomposites could be immobilized on the Au film with a magnetic pillar. The antibodywas bound to Fe3O4-AuNR nanocomposites with MPA, and then the binding of antigen toantibody lead to change in the dielectric constant on the biosensor surface, which can beeasily detected with the SPR biosensor. The SPR biosensor based on Fe3O4-AuNRnanocomposites shows a good response to goat IgM in the concentration range of0.15-40.00μg mL-1, while the SPR biosensor based on MPA shows a good response to goatIgM in the concentration range of1.25-40.00μg mL-1. The experimental results indicatedthat the application of Fe3O4-AuNR nanocomposites considerably improved theperformance of SPR biosensor.To take advantages of gold nanorods (GNRs) and Fe3O4nanoparticles, GNR-Fe3O4nanohybrids were prepared and applied in SPR biosensor for the determination of mouseIgG. The premade negatively charged Fe3O4nanoparticles were coated on the surface ofpositively charged GNRs through electrostatic interaction. The synthetic method wassimple, quick and easy operation. The aldehyde group functionalized GNR-Fe3O4nanohybrids possess unique magnetic property, exceptional optical property and goodbiocompatibility, which can be used as immobilization matrix for biomolecules. Themagnetic nanohybrids can be easily immobilized on the surface of SPR biosensor chipwith a magnetic pillar, which simplifies the experimental procedure. The amine group ofthe antibody can be bound with the terminal aldehyde group of the nanohybrids throughSchiff alkali reaction. The lowest concentration of mouse IgG that can be detected with theproposed biosensor is0.15μg mL-1，which is16times lower than that detected with the biosensor based on MPA.Graphene oxide (GO) can serve as good support for biomolecules through electrostaticinteraction, covalent and non-covalent binding, due to its large surface area, flat surface,rich in π conjugated structure and oxygen-containing functional groups, goodbiocompatibility. A GO-based SPR biosensor for detection of human IgG was presented.Since GO has many negative charge groups such as carboxylic acids, hydroxyl groups, andepoxides, GO sheets can be assembled on a positively charged SPR Au film via electronicinteraction. The goat anti-human IgG is immobilized on the GO through covalentattachment between the amine group and the carboxyl group. Thus human IgG can bedetected based on specific antibody-antigen interaction. The experimental results indicatedthat the amount of goat anti-human IgG immobilized on the sensor based on GO is muchlarger than that immobilized on the sensor based on MPA. For the sake of sensitivityenhancement further, when antibody was immobilized on the sensor surface, the antigencoupled with AuNRs was detected. When GO and AuNRs were used, the sensitivity ofSPR biosensor was remarkably enhanced and the lowest concentration of human IgG thatcan be detected is0.075μg mL-1.When graphene was combined with other materials including polymer, semiconductorand metal nanoparticles, it will show diverse properties, such as excellent catalytic property,conductivity and unique optical property. Novel SPR biosensors based on Au-graphene(Au-Gra) nanohybrids and Ag-graphene (Ag-Gra) nanohybrids for the detection of mouseIgG were developed. The biosensors are label free, and have high sensitivity and selectivityfor biosensing. Au-Gra and Ag-Gra nanohybrids were synthesized in a simple, effectiveand rapid way. These nanohybrids were assembled on the Au film through1,6-hexanedithiol by covalent attachment. And the antibody was bound to the nanohybridsthrough3-mercaptopropinic acid. The biosensors based on Au-Gra nanohybrids andAg-Gra nanohybrids show a good response to mouse IgG in the concentration range of0.30-40.00μg mL-1and0.15-40.00μg mL-1, respectively. As a result, Ag-Gra nanohybridsshow higher sensitivity than Au-Gra nanohybrids when they were applied in SPR biosensor.GNRs and GO were used to enhance the sensitivity of wavelength modulation SPRbiosensor to detect bovine IgG. GNRs exhibit two plasmon absorption bands correspondingto the transverse band and the longitudinal band. The longitudinal plasmon absorption bandis extremely sensitive to the change in the dielectric properties of the surroundings and thesensitivity increases as the aspect ratio of GNRs increases. GNRs were positively chargedbecause of the CTAB on the surface and can be immobilized on the Au film through1,6-hexanedithiol by covalent attachment. Then the negatively charged GO can be attachedto the sensor surface via electrostatic interaction with GNRs. Meanwhile, GO was used asa support to immobilize antibody directly. The SPR biosensor based on GNR/GO sensingmembrane shows a good response to bovine IgG in the concentration range of0.075-40.00μg mL-1. The lowest concentration of bovine IgG obtained with the biosensor modifiedwith GNRs and GO is32times lower than that obtained with MPA membrane biosensor.Therefore, GNRs and GO can be used to enhance the sensitivity of the SPR biosensorsignificantly for the determination of bovine IgG.Different shapes of gold nanoparticles have been prepared and used to constructbiosensors using scheme of sandwich assays for detecting human IgG. The detection hasbeen carried out using both SPR and electrochemical methods. Gold nanorods (GNRs) andgold bipyramids (GBPs) were synthesized by a method of seed-mediated growth. Thesurface of gold nanoparticles were further activated with alkanethiols for attachment of theantibody, and this gold nanoparticles-antibody conjugates were used as the secondaryantibody. The results obtained from complimentary methods have been comparied. GNRsand GBPs have been demonstrated to be beneficial for the performance improvement ofdetection. The lowest concentration of human IgG obtained with the biosensor modifiedwith GNRs and GBPs were16times and64times lower than that obtained with thebiosensor without using gold nanoparticles, respectively. Moreover, the detection limitsobserved in this study show that electrochemical method is consistently more sensitive thanSPR.