We report a sensitive D-shaped photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensor with linear sensing performance and a broad detection range for low refractive index (RI) liquid analytes ranging from 1.27 to 1.37 with possible extension beyond this range. We examine three combinations of materials (silver only, graphite on silver, and graphene on silver) as plasmonic nanofilm for the PCF-SPR and demonstrate that graphene-assisted PCF has the best overall performance. We show that graphene coating of silver nanofilm improves the sensitivity and the overall figure of merit of the sensor, besides the practical benefit of protecting the silver nanofilm from surface oxidation. Furthermore, we propose two distinct ways of analyte sensing based on filling patterns where the liquid analyte can be filled internally into the top two air holes of the PCF, or externally into a rectangle channel at the top of the fiber. In the internal filling detection scheme, the graphene-assisted PCF-SPR sensor demonstrates ultra-linearity, a detection range of 0.1 refractive index unit (RIU) between 1.27 and 1.37, an average linear spectral sensitivity of 2320 nm/RIU, and a maximum amplitude sensitivity of 192 RIU⁻¹ for 1150 nm excitation. In the external filling detection scheme, the PCF-SPR exhibits extremely large sensitivities with a maximum spectral sensitivity of 22,400 nm/RIU close to analyte RI of 1.33, and a maximum figure of merit (FOM) of 127 which is approximately five times larger than that of the similar reported PCF-SPR sensors in the literature. The combination of a broad detection range for low-index analytes, large sensitivities, design flexibility, and stability against surface oxidation renders our proposed sensor as an interesting candidate for biosensing applications in chemistry, biology, and medicine.

我们报告了一种灵敏的D形基于光子晶体纤维的表面等离振子共振（PCF-SPR）传感器，具有线性感应性能，并且对低折射率（RI）液体分析物的检测范围很广，范围为1.27至1.37，并且可能会扩展到该范围之外。我们研究了三种材料组合（仅银，石墨在银上和石墨烯在银上）作为PCF-SPR的等离子体纳米薄膜，并证明了石墨烯辅助PCF具有最佳的整体性能。我们显示，除了保护银纳米膜免受表面氧化的实际好处之外，银纳米膜的石墨烯涂层还可以提高传感器的灵敏度和整体品质因数。此外，我们基于填充模式提出了两种不同的分析物检测方法，其中液体分析物可以内部填充到PCF的顶部两个气孔中，也可以外部填充到光纤顶部的矩形通道中。在内部填充检测方案中，石墨烯辅助的PCF-SPR传感器表现出超线性，检测范围为0.1折射率单位（RIU）在1.27和1.37之间，平均线性光谱灵敏度为2320 nm / RIU，并且最大振幅灵敏度为192 RIU^-1对于1150 nm激发。在外部填充检测方案中，PCF-SPR具有极高的灵敏度，其最大光谱灵敏度为22,400 nm / RIU，接近分析物RI为1.33，最大品质因数（FOM）为127，约为其的五倍。与文献中报道的类似PCF-SPR传感器相同。低折射率分析物的广泛检测范围，高灵敏度，设计灵活性以及对表面氧化的稳定性的结合，使我们提出的传感器成为化学，生物学和医学领域生物传感应用的有趣候选者。