| The detection of biochemical molecules plays a vital role in pharmacological research and early diagnosis.Generally,the target molecules are often present at very low concentrations,and the sample also contains a variety of other molecules,making their identification a strenuous task.With the rapid development of bioinformatics,structural biology,and gene therapy,biomedicine is drawing more and more towards microcosmic schemes,a detection platform featuring high performance and low cost is of great significance for the early diagnosis,prevention,and treatment of diseases.Microfluidics can analyze and process fluidics at the micro-scale,providing an ideal solution for the detection of high throughput and small dose samples.But high sensitivity and large dynamic range detection are great challenges for such little volume liquid.The optical fiber SPR sensor has advantages of anti-electromagnetic interference,miniaturization,easy surface modification,and label-free,which can solve the above problems.Based on the resonant coupling theory of SPR,this thesis focuses on the issues such as the fabrication of optical fiber microfluidic devices,sensitivity improvement of SPR sensors,and the RI detection with large dynamic range.SPR microfluidic sensing schemes based on different configurations of the optical fiber are proposed,and the feasibility is demonstrated through theoretical analysis and experiments,which provide a reference for microfluidic applications of the optical fiber SPR sensor.The main innovative research results are as follows:（1）For high integration of microfluidic devices,an SPR sensor based on a hollow hanging-core fiber（HHCF）is proposed.There is a large air hole in the HHCF（130μm in diameter）,which is propitious for metal deposition and infiltration of liquid samples.Through the laser etching technology,the cladding of the HHCF is opened to expose the core.The gold film is deposited on the surface of the hanging-core through a plasma sputtering apparatus for SPR excitation.The relationship between the gold film thickness and the testing sensitivity is studied.The thicker the gold film,the longer the resonance wavelength,and the higher the testing sensitivity.The testing sensitivity is in the range of 1440 nm/RIU to 2010 nm/RIU when the gold film thickness range is 30-70 nm with the sample RI range of 1.333-1.433.The BSA concentration is measured and the sensitivity is 6.19 nm/（mg/m L）.The microfluidic SPR sensor prepared by the HHCF can integrate the detection of little volume liquid into a fiber,further reducing the size of the device.（2）For sensitivity enhancement of microfluidic devices,an SPR sensor based on all-fiber Bessel-like beams is proposed.A section of SMF and a section of MMF are spliced together to construct the Bessel-like beam.The Bessel-like beam contains a series of concentric annular light fields,the number of which is determined by the length of the MMF.A dual-truncated-cone structure of the fiber is fabricated to excite and receive SPR signals,the effects of different Bessel-like beams and grinding angles on the sensor performance are studied.The performance of the sensor can be significantly improved by increasing the grinding angle and the number of concentric annular light fields on the fiber end face,the measured maximum sensitivity is6908.3 nm/RIU,and the detection limit can reach the order of 10-6 RIU.When the sensor is used for the detection of BSA,the sensitivity is 8.77 nm/（mg/m L）.The proposed sensor uses Bessel-like beams as the input source which reduces the divergence of the resonance angle and is more sensitive than the optical fiber SPR sensor using Gaussian beams as the input source.（3）For large dynamic range RI detection of microfluidic devices,a tapered fiber optic SPR sensor based on the polymer coating is proposed.The tapered fiber is prepared by the melting and pulling method,then,the 532 nm laser is coupled into the fiber through a spatial optical coupler to cure the photopolymer coating,and a thin gold film is deposited on the surface of the coating to construct the sensing region.The effects of different polymer coating thicknesses on the sensor performance are studied.The RI sensitivity decreases with the increase of the coating thickness.When the coating thickness is 1.8μm,the sensor measures the RI sensitivity as 6422.9 nm/RIU（RI:1.423-1.493）and 1332.9 nm/RIU（RI:1.333-1.403）,respectively.In addition,the temperature response characteristic of the sensor is investigated experimentally.When the coating thickness is 1.8μm with the temperature range of 20-50°C,the sensitivity reaches 1.43 nm/°C.When the sensor is used for the detection of Ig G,the sensitivity is measured as 0.06 nm/（μg/m L）.This work further improves the RI detection range of the SPR sensor by increasing the RI of the waveguide,and expands its application in the field of biochemistry. |
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