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Optical Biosensors Based On Nanostructured Waveguiding Layer

Posted on:2015-06-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y FanFull Text:PDF
GTID:1108330476455938Subject:Physics
Abstract/Summary:PDF Full Text Request
Simple, rapid and sensitive detection of analytes becomes increasingly important in many fields such as environmental monitoring, food control and medical diagnostics. Optical biosensors based on optical waveguide(OWG) and surface plasmon resonance(SPR) have been pushed forward extensively in these areas.In the study, we first applied the nanoporous waveguide(NPWG) biosensor based on nanoporous anodic alumina/aluminum(PAA/Al) bilayer to the fluorescence enhancement experiments. According to the simulation results, the electric field strength within the PAA layer increases with decreasing the RI of the PAA, which can be easily achieved by dissolving a part of PAA in a phosphoric acid solution. Compared to the biosensors based on SPR and total internal reflection(TIR) structure, much stronger fluorescence signal enhancement was achieved by the presence of NPWG. From the experiment results, the PAA/Al film with TE0 mode exhibits more than 140-fold larger fluorescence response compared to the TIR structure. As an application of using NPWG, the PAA/Al bilayer with optimized structure which supports TE0 mode was adopted to investigate of hybridization between Alexa Fluor? 488 labeled target DNAs(d A15) and the probe DNAs(d T22) by monitoring the fluorescence kinetic curve. Compared to the results obtained using non-complementary target DNAs(d T15), the hybridization behavior did happen between the dA15 and the dT22. On the other hand, limit of detection(LOD) is also estimated for d A15 using NPWG and amount of 20 p M was achieved.For improving the detection sensitivity and the aqueasous stability of the sensor chip, we applied the surface sol-gel(SSG) method to attach a highly ordered, free-standing PAA film to a gold substrate and used as SiO2 coated NPWG. The Si O2 coating here has two uses: as “nano glue” and to create a protective layer for the PAA film against etching in aqueous solution. The feasibility of the Si O2 coated NPWG was demonstrated by monitoring the adsorption of BSA and streptavidin molecules. Furthermore, improved sensitivity was achived by attaching a thicker PAA film to a gold substrate. Basd on the method, a new optical biosensor based on silica nanotube(SNT) array was realized through dissoving the PAA template. A high value of 552 RIU-1 as the sensing figure of merit(FOM) was achieved by solvent exchanging experiment, which is higher than other biosensors based on angular modulation. The practical usefulness of SNTWG which supports a TM1 mode was tested by detection streptavidin using a standard biotin-streptavidin affinity model, and the LOD of the SNTWG for detection of streptavidin was estimated as 93 pM. According to the Fresnel simulation, the angular shift of TM1 mode is 7 times larger than that of conventional SPR.
Keywords/Search Tags:optical waveguide, porous anodic alumina, nanotube array, silica, biosensing
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