Study And Experiment Of SPR Bio-molecule Probe Based On TFBG

Surface plasmon resonance (SPR) sensor is a kind of optical transducer. It is based on the principle that the propagation constant of the surface plasmon wave propagating at the interface of a metal film and a dielectric is very sensitive to the Surrounding-medium Refractive Index (SRI). Because the SPR sensor retains a lot of advantages,such as label-free, online detection, anti-emi and imple set-up required, it is studied and applied greatly. TFBG (tilted fiber Bragg grating) and FBG (fiber Bragg grating) are both short period fiber gratings,but the difference between them is that the grating plane of TFBG is tilted by an angle. So TFBG can couple the core mode to a series of contra-propagating cladding modes, and the cladding modes can excite surface plasmon wave. So the TFBG and SPR technology are combined to make up a biomolecule probe based on TFBG-SPR.The basic principle of TFBG and SPR as well as kinds and detection measurements of SPR is presented in this paper. Meanwhile, the effect of temperature on SPR is analysed. Then the transmission spectrums and cladding modes in different solutions are simulated by OptiGrating. By the graphic observation and data analysis, a preliminary conclusion is got that in a certain sensing scope, the cladding modes of TFBG shift slightly to right with the increasing of SRI, and the relation between resonance peak caused by the coupling of core mode and a certain cladding mode and the SRI is linear. Then the45nm thick gold coating is deposited on the surface of the TFBG cladding in a small-scale sputtering chamber KYKY SBC-12, and thermal field scanning electron microscopy presentes that the effect of gold-coating is satisfying in the term of microscopic level. The refractive index(RI) sensing experiments of different concentration solutions of NaCl、MgCl2、CaCl2are carried out using bare and gold deposited TFBG. The RI sensing characteristics of both bare and gold deposited TFBGs respectively are studied by experiments. Meanwhile, it proves the conclusion that the cladding modes of TFBG drift to right gradually when the SRI is increasing and the relation between resonance peak caused by the coupling of core mode and a certain cladding mode and the SRI is linear. And by quantitative analysis, we know that SPR sensor by the deposited namoscale gold layer on the surface of cladding enhances the RI sensitivity dramatically from2nm/RIU to500nm/RIU, which is200to300times larger than that of the bare TFBG approximately. The linear fittings of resonance peak caused by the coupling of core mode and a certain cladding mode and SRI of bare and gold-coating SPR sensor are very good and both of them are up to more than0.99.Rhodaneses gene in acidithiobacillus ccddus is modified based on the above TFBG-SPR sensor to be a biomelcule probe. And the modifying effect of biomolecule sensitive membrane is detected by biological method and optical method. DNA amplification shows that the sensitive membrane modification is satisfying and the change of resonance peak during modification indicates the molecular modification is conducting continuously. Hybridization experiments between fixed DNA probe and two different concentrations complementary DNA probe prove that the resonance peak is changing continuously during hybridization, so it demonstrates that the biomolecule probe based on TFBG-SPR is able to carry out specific detection.