Surface Plasmon Resonance Biosensor Based On Tilted Fiber Bragg Grating

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). Commercialized SPR sensors based on bulk optical device such as prism have been available long ago. The research focus of SPR sensors now is to realize the miniaturization and microminiaturization of the SPR sensor system by utilizing optical waveguide as the couple device. This thesis proposed a new design of fiber optic SPR sensor based on tilted fiber Bragg grating (TFBG) after a comprehensive review of previous research work on the relative subject. Then the proposed TFBG-SPR was fabricated and its potential as a biosensor was verified by two bio-specific interaction analysis (BIA) experiments.TFBG (tilted fiber Bragg grating) and FBG (uniform fiber Bragg grating) are both belong to short period fiber gratings, the difference between them is that the grating plane of TFBG is not parallel to the cross-section of the fiber but is tilted by an angle. This unique structure of TFBG make it can couple the core mode to a series of contra-propagating cladding modes which can be used to excite surface plasmon wave. Thus TFBG is very suitable to be used as an optical couple device for a fiber optic SPR sensor.The proposed TFBG-SPR sensor was fabricated by coating the cladding surface of TFBG with a gold film of which the thickness is about 50 nm. The cladding modes that fulfill some particular conditions will excite surface plasmon resonance at the gold-dielectric interface and lose their energy, and the energy loss will cause a change in the transmission spectrum of TFBG-SPR sensor. By interpreting the spectrum of TFBG-SPR sensor we can deduce the characteristics of the dielectric at the gold surface, and this is the sensing principle of TFBG-SPR sensor. Compared with the former SPR sensors based on fiber optic devices, the TFBG-SPR sensor does not require a modification of the fiber structure thus makes the manufacture process easier as well as maintains the robustness of the sensor.A TFBG-SPR biosensor can be realized by a farther deposition of bio-sensitive film on the surface of the gold film. The deposition process of bio-sensitive film was elaborated in this thesis and then the TFBG-SPR biosensor was verified by an antigen-antibody immunoreactions experiment and a DNA hybridization experiment. Both of the two experiments demonstrated the capability of TFBG-SPR sensor to monitor bio-specific interaction between bio-molecules.