| Long-range surface plasmon resonance(LRSPR)is a special electromagnetic-field mode excited by adding a dielectric buffer layer with low refractive index(RI)between substrate and metal layer on the basis of conventional SPR.Because of the low loss,long propagation distance and deep penetration depth of the surface plasmon polaritons(SPPs)in LRSPR sensor,LRSPR sensor possesses better performance indexes such as sensitivity,full width at halfmaximum(FWHM),and RI resolution compared with conventional SPR sensor.Therefore,LRSPR sensor is more suitable for the detection of biological macromolecules and even cellular structure.Based on the above,this paper carried out the research of optical fiber LRSPR sensor and its biological detection application.The main contents of this paper are as follows:(1)By analyzing the current status of LRSPR sensing application,human immunoglobulin G(hIgG)detection,and side-polished fiber SPR sensor research,a side-polished single-mode fiber LRSPR sensor was proposed to realize the detection of hIgG with different concentration.(2)A series of mathematical models were established to illustrate LRSPR theory intuitively.The advantages and disadvantages of LRSPR sensor compared with conventional SPR sensor were analyzed from different aspects of metal layer type,sensitivity,FWHM,figure of merit(FOM),etc.The simulation models of the side-polished fiber LRSPR sensor were established by using finite-difference beam propagation method(FD-BPM),transmission matrix method(TMM),and finite element analysis(FEA).(3)The sensor parameters including resonance wavelength,resonance depth,and FWHM were introduced.The structural parameters of the LRSPR sensor were optimized by using TMM supported by FD-BPM and FEA.The RI sensing performance of the conventional SPR sensor,the asymmetrical LRSPR sensor,and the symmetrical LRSPR sensor were simulated and analyzed by using TMM.The results showed that the symmetrical LRSPR sensor had the best performance and its FOM was up to 107.52 RIU-1.(4)The instruments and chemical reagents involved in the experiment were introduced.The conventional SPR sensor,asymmetrical LRSPR sensor,and symmetrical LRSPR sensor were fabricated.The RI sensing experiments of the three kinds of sensors were carried out,and the results showed that the symmetrical LRSPR sensor had the best performance and its FOM was 64.26 RIU-1.Meanwhile,the RI sensing performance among the three kinds of sensors as well as between the symmetrical LRSPR sensor and other reported sensors were compared and analyzed.The asymmetrical LRSPR sensor was utilized to realize the simultaneous measurement of RI and temperature at the exactly same position.(5)The near-field electronic coupling between the long-range SPPs and the localized SPPs was explained,and the simulation model of the gold nanoshell modified asymmetrical LRSPR sensor was established as well as its mode-field distribution was analyzed.The results showed that the electric-field intensity on the gold nanoshell surface was significantly enhanced compared with that of the gold layer surface of the unmodified LRSPR sensor.Based on the coupling effect between the two SPPs,the limit of detection(LOD)of the developed sensor was as low as 0.20 μg/mL.Also,the real sample was detected,and the results showed that the non-specific interaction induced by serum matrix was acceptable,indicating the developed sensor had good practicability.Based on a review of the current status of LRSPR sensing applications,this paper carried out theoretical research on LRSPR,sensor numerical simulation research,RI and biosensing experimental research,and finally realized the detection of hIgG with high sensitivity and low LOD,providing a solution for the detection of biological solution with low concentration. |
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