| Optical fiber sensors have unique advantages in biomedicine,environmental health,food safety and other fields because of their simple structure,low cost,anti-electromagnetic interference,and suitability for distributed sensing,which have attracted extensive attention of researchers.In fiber-optic biochemical sensors,enhancing the interaction of light with target objects is crucial to achieve high-sensitivity detection.However,the common fiber gratings such as long-period fiber grating(LPFG)and tilted fiber grating(TFG)are limited in their sensitivity improvement and application in biochemical detection because the optical field is mainly limited to the fiber core.Compared with the above fiber gratings,the microfiber itself has a strong evanescent field effect,which provides a new platform for the interaction of light and matter,and can realize label-free,fast response,and high-sensitivity detection of biochemical substances at the trace level.In this paper,a microfiber biosensor integrated with GO was constructed by virtue of the ingeniously designed microfibers of different diameters as biosensing carriers and the optical and physical functional properties of a novel two-dimensional nanomaterial graphene oxide(GO).GO was appropriately integrated on the surface of microfiber through covalent bonding and physical adsorption,providing abundant binding sites for molecular recognition elements assembled on the surface of microfiber.The functionalized optical microfiber biosensor obtains high-sensitivity refractive index sensing detection and high-specificity recognition ability,and converts the information of the refractive index change on the sensor surface caused by the specific binding of the molecular recognition element and the target molecule to be measured into the change signal of the optical interference spectrum,thereby realizing the identification of biomolecules-rabies virus(RV)detection experiment.(1)The optical waveguide theory,single-mode conditions and optical field distribution characteristics of microfiber are described in detail,and the effects of different conditions on the energy distribution characteristics of the evanescent field of microfiber are simulated and analyzed.Theoretical research and simulation analysis of the refractive index sensing performance of the dual-mode interferometric microfiber at the dispersion turning point are carried out to provide theoretical guidance for the subsequent experimental basis.(2)The preparation method of the the dual-mode interferometric microfiber and the simulation experiment of the refractive index of the microfiber are studied,and the microfiber is used for the detection of the refractive index experiment.Firstly,the ordinary single mode fiber was discharged into a double-tapered fiber by a fiber fusion splicer,and then the tapered fiber was put into the fiber fusion taper machine to produce a 10?m microfiber.Then,the refractive index sensing theory previously briefly analyzed before is further deduced in detail,and the theoretical refractive index(RI)sensitivity of 1196nm/RIU is obtained by simulating a 10?m microfiber.Finally,the experimental verification of the refractive index of the prepared microfiber using different concentrations of refractive index matching liquid was carried out,and the experimental RI sensitivity of 1079nm/RIU was obtained,and the reasons for the gap between the experiment and the theory were analyzed.(3)A rabies virus(RV)immunosensor based on GO functionalized on the surface of the microfiber was prepared,and the immunosensor was used to detect RV antibodies and complete specific and clinical detection.Firstly,a microfiber with a diameter of 7.5?m was fabricated by the previous preparation method,and the high RI sensitivity of the microfiber at 1757 nm/RIU was obtained through the refractive index calibration experiment.Then,GO was integrated on the surface of the microfiber in the form of covalent bonding,and the molecular recognition element-RV antigen(RV-Ag)was assembled on the surface of the microfiber to realize the RV biosensor based on the GO microfiber.The experimental results show that the immunosensor has a detection sensitivity of 1.099 nm/log(mg·mL-1)for RV antibodies in the detection range of 200fg/mL?1 ng/mL,and the detection limit is about 225.56 fg/mL,the saturation concentration is about 1 ng/mL,and the dissociation coefficient is about 2.92×10-11 M..When the immunosensor was used for the specific detection of different biological antibodies and the clinical detection of RV positive serum with different concentrations,the immunosensor had a very weak response to different kinds of biological antibodies,and had an obvious response to RV positive serum.The above experiments demonstrate that the biosensor can provide high sensitivity biological trace detection capability for specific selection. |
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