Biosensing Research Based On SPR Effect Of Multimode And Coreless Fiber

Surface Plasmons are electron-dense waves that propagate along the metal surface by the interaction of free-vibrating electrons and photons.Fiber optic sensors excited by surface plasmons,commonly referred to as surface plasmon resonance(SPR)sensors,are a type of refractive index sensing device.When the energy and momentum of the incident light match the energy and momentum of the surface plasmon wave(SPW),the SPR can be excited at the interface between the metal film and the dielectric.The energy carried by the photons is coupled to the electrons in the metal,thereby achieving a sharp resonance drop in light intensity.The propagation constant of SPW is closely related to the refractive index(RI)of the surrounding medium.Therefore,even a very small change in the refractive index near the thin metal layer can produce a measurable shift in the resonant wavelength.(1)Our first research was that we report a D-type optical fiber biosensor for human immunoglobulin G(HIg G)detection based on surface plasmon resonance(SPR).The SPR phenomenon was both simulated by COMSOL and observed experimentally.To fabricate the sensor,the cladding of a multimode optical fiber(MMF)was polished using a grinding wheel to obtain a D-type cross-section.Next,a gold film was sputtered on the surface of the MMF.The optimal gold layer thickness and grinding depth were determined through simulations.As per the experimental results,the optimized sensor exhibited high refractive index(RI)sensitivity,which ranged from 1590.9 nm/RIU to3513.3 nm/RIU for RI values of 1.343 to 1.373.Subsequently,Poly dimethyl diallyl ammonium chloride(PDDA)and Poly(sodium-p-styrenesulfonate)(PSS)were deposited four times in sequence to form polyelectrolyte self-assembled multilayers for the surface functionalization of the fiber.HIg G and goat anti-HIg G(Ga HIg G)were chosen as the bioconjugate pair for evaluating the functionality of the fabricated biosensor,and the sensitivity to Ig G was determined to be 91 nm/(mg/ml).The specificity of the biosensor was also verified through comparison tests performed using gelatin,horse Ig G,and swine Ig G.The obtained results confirmed the suitability of the biosensor for use in various biochemical applications.(2)Our second research presents a facile,rapid and effective method for the fabrication of optical fiber surface plasmon resonance(SPR)biosensors.A section of coreless fiber is spliced between two multimode fibers to construct a multimodecoreless-multimode(MCM)fiber structure.We take full advantage of the transmission characteristics of the coreless fiber,and the experimental results confirm that this MCM after coating with a thin gold film is able to excite surface plasmon wave effectively.Three sensors with different lengths of coreless optical fibers of 1 cm,1.6 cm and 2 cm were constructed.And when the refractive index of the sucrose solution changes from1.33 to 1.3883,the refractive index(RI)sensitivity was measured to be 2129.66nm/RIU,2249.33 nm/RIU and 2307.93 nm/RIU,respectively.After a comprehensive comparison,we chose the MCM optical fiber sensor with a coreless fiber length of 1.6cm for biological experiments.After directly immobilized the antibody on the gold film,the biosensor was able to selective detect human immunoglobulin G(HIg G)with a sensitivity of 215 nm/(mg/m L).The limit of detection is 0.093 ?g/m L.The biosensor exhibited effective antibody immobilization ability and high sensitivity for HIg G detection,which fully demonstrates its potential applications in the broader biomedical or chemical field.