Research On Cladding-type SPR Sensor Based On Twisted Optical Fiber And Its Biochemical Applicatio

Optical fiber surface plasmon resonance(SPR)sensor has attracted more and more attention due to its unique advantages such as high sensitivity,compact structure,strong anti-electromagnetic interference ability,and is widely used in food safety,environmental monitoring,life science and other fields.The fabrication of fiber core SPR sensor needs to remove part of the cladding of the fiber to expose the fiber core.Although this can adjust the resonant wavelength range of the sensor well,there are problems such as weak structure and cumbersome fabrication process;The purpose of the cladding type SPR sensor is to realize the mode coupling between the fiber core and the cladding,without exposing the fiber core by removing the cladding,which has little impact on the physical strength of the fiber.Therefore,the cladding type SPR sensor has the advantages of simple fabrication and high physical strength.However,there are few reports about the clad SPR sensor at present,and further research is needed.Twisted fiber structure is a special structure formed by making a twisted area on the fiber.This structure not only has high physical strength,but also can optically couple the fiber core into the fiber cladding through the twisted structure.The optical fiber cladding SPR sensing can be realized by coating the outer surface of the cladding behind the torsion zone with a gold film.Focusing on the characteristics of twisted optical fiber to realize the coupling of core light to cladding mode,this paper proposes a cladding SPR sensor based on twisted optical fiber and applies it to the field of biochemical detection,mainly including the following contents:(1)The cladding SPR sensor based on single-mode twisted optical fiber is manufactured,and the optical fiber SPR refractive index measurement system is built.The experimental results show that the sensitivity and sensing range of the clad SPR sensor can be adjusted by controlling the pitch of the twisted optical fiber.(2)Based on the results of pitch optimization of single-mode twisted optical fiber,the types of optical fiber used for manufacturing twisted optical fiber are optimized.Research shows that the step-index multimode fiber,the twisted multimode fiber clad SPR sensor,which is made of the raw material of twisted fiber,has the highest sensing sensitivity.(3)Based on the research of twisted SPR sensor,a kind of twisted tapered fiber cladding SPR sensor is proposed by introducing a conical structure into the twisted area of the twisted fiber,and the size of the taper waist diameter and the diameter of the twisted taper area are optimized.The experimental results show that the taper waist diameter is78 μ M has the highest sensing sensitivity.(4)Biochemical sensing:(1)The outer surface of the clad SPR sensor based on single-mode twisted optical fiber was successively modified with chitosan and polyacrylic acid(PAA),and the effective adsorption of chitosan and PAA on copper ions was used to realize the measurement of copper ion solutions with different concentrations;(2)After the outer surface of the clad SPR sensor based on multimode twisted optical fiber is successively modified with metal-organic framework material(ZIF-67),staphylococcal protein A(SPA),growth differentiation factor(GDF11)antibody,and bovine serum albumin(BSA),the specific detection of different concentrations of GDF11 antigen is realized;(3)The outer surface of the SPR sensor based on the twisted triconical cladding was successively modified with polydiallyl dimethyl ammonium chloride(PDDA)and sodium polystyrene sulfonate(PSS)to realize the detection of nitrite ion concentrations of different concentrations.Compared with the sensing performance of similar optical fiber sensors,the sensor proposed in this paper has made breakthroughs in sensitivity and detection limit.