开放式多通道多芯少模光纤表面等离子体共振生物传感器

Multi-channel few-mode multicore fiber based surface plasmon resonance biosensor with open air-hole

基于多芯少模光纤结构特性,提出了一种具有开放式感知通道的多芯少模光纤表面等离子体共振生物传感器.建立了多芯少模光纤表面等离子体共振生物传感器的模型,利用有限元方法分析了纤芯气孔间距、膜层厚度、膜层材料以及不同传输模式对传感器性能的影响,并讨论了传感器多通道感知性能.仿真分析发现,纤芯气孔间距决定了倏逝波的耦合强度,材料特性和模式共同影响了表面等离子体共振峰的位置和灵敏度.经过计算可知:当单个凹槽传感通道上沉积100 nm铟锡氧化物薄膜,分析物折射率范围为1.33—1.39时,LP11ax模式对应的平均光谱灵敏度为12048 nm/RIU(其中RIU为折射率单位,即refractive index unit),最高灵敏度为20824.66 nm/RIU,最大折射率分辨率可达4.8×10^–6 RIU;当光纤外围凹槽镀上不同厚度的金膜、银膜和铟锡氧化物膜时,既可以单独探测生物物质,也可以联合检测同一生物物质,实现了传感通道的控制灵活性和测试物质的多样性.

Based on the structural characteristics of the few-mode multicore fiber(FM-MCF),a multi-channel FMMCF surface plasmon resonance(SPR)biosensor with open air-hole is presented.Due to the air-hole distribution of the FM-MCF,the six outer air-holes naturally become open air-holes,i.e.groove sensing channels,fabricated by chemical etching.Then,compared with D-shape structure,tapered structure of fiber and air-hole of photonic crystal fiber(PCF),the open groove structure is easy to accommodate the liquid analyte.In order to obtain better sensing performance,a sensing model of the presented FM-MCF SPR biosensor with sensitive dielectric layer is established and numerical simulations are performed using the finite element method.In the simulations,the effect of core-hole distance,coating thickness,sensing dielectrics,transmission modes in optical fiber on the sensing performance as well as the role of multi-channel are analyzed.The simulation results show that when the air-hole is tangent to the core(d=0μm),the FM-MCF SPR biosensor has the better performance because the core-hole distance d determines the leakage intensity of the evanescent wave.As the evanescent field excited by high-order mode(LP11ax mode)is stronger than that by fundamental mode(LP01x mode),the performance of biosensors for SPR excitation by using high-order mode is better than by using fundamental mode.Meanwhile when the coating thickness of gold,silver and indium tin oxides(ITOs)is 40 nm,30 nm and 100 nm respectively,the FWHM of loss spectrum reaches a minimum value,which means that the presented biosensor has the better performance in this sense.For the case of different sensing dielectrics,it is observed that the resonance wavelength of gold and silver film are in the visible wavelength range,while the ITO is at near-infrared wavelength.Then it is useful for our biosensor to simultaneously detect many liquid analytes in one SPR transmittance spectrum.In addition,the calculation results also show that when one of the groove channels is coated with 100 nm ITO for the LP11ax mode,the FM-MCF SPR biosensor has a highest sensitivity of 20824.66 nm/RIU and refractive index(RI)resolution is 4.8×10^–6 RIU with the surrounding RI changing from 1.33 to 1.39,in which the RI of bovine serum albumin(BSA)solution,human Immunoglobulin G and C-reactive protein can be detected.Moreover,when the outer groove channels of our biosensor are coated with gold,silver and ITO film with different thickness,many biological liquid analytes can be detected separately or the same biological liquid analyte can be detected jointly,which reveals that the control flexibility of the groove sensing channel and the diversity of the detection analytes.