In this paper, we propose and demonstrate a high-performance mercury ion sensor with sub-nM detection limit, high selectivity, and strong practicability based on the small molecule of the 4-mercaptopyridine (4-MPY) modified tilted fiber Bragg grating surface plasmon resonance (TFBG-SPR) sensing platform. The TFBG-SPR sensor has a rich mode field distribution and a narrow bandwidth, which can detect the microscopic physical and chemical reactions on the sensor surface with high sensitivity without being disturbed by the external temperature. For the environmental compatibility and highly efficient capture of the toxic mercury ion, 4-MPY is modified on the sensor surface forming a stable (4-MPY)-Hg-(4-MPY) structure due to the specific combination between the nitrogen of the pyridine moiety and the Hg²⁺ via multidentate N-bonding. Moreover, gold nanoparticles (AuNPs) are connected to the sensor surface through the (4-MPY)-Hg-(4-MPY) structure, which could play an important role for signal amplification. Under the optimized conditions, the limit of detection of the sensor for mercury ions detection in the solution is as low as 1.643×10^–10 M (0.1643 nM), and the detection range is 1×10^–9 M – 1×10^–5 M. At the same time, the mercury ion spiked detection with tap water shows that the sensor has the good selectivity and reliability in actual water samples. We develop a valuable sensing technology for on-time environmental Hg²⁺ detection and in-vivo point of care testing in clinic applications.

基于倾斜光纤光栅模式耦合理论,研究了倾斜角度对光纤光栅光谱特性的影响,并应用OptiGrating 软件进行数值模拟仿真。通过对不同倾斜角度得到的光纤光栅反射谱及透射谱的研究发现,随光栅倾角的增大,布拉格波长的中心波长偏移,同时反射率下降,而包层模式耦合增强,透射损耗变大,群时延减小。仿真结果对光纤光栅的设计和优化有一定的指导意义。

根据倾斜光纤光栅(TFBG)和表面镀金的TFBG传感器测量折射率的基本原理, 通过OptiGrating软件模拟了不同浓度溶液下TFBG的透射谱和芯层模与某阶包层模耦合引起的谐振峰, 初步得出了TFBG各阶包层模随着外界折射率的增大而向右偏移、 在一定的传感范围内中心波长与外界折射率呈线性关系的结论。 用小型离子溅射仪对TFBG镀45 nm厚度左右的金膜, 并用扫描电镜在微观上观察镀膜效果。 通过不同浓度下的NaCl溶液、 MgCl2溶液、 CaCl2溶液实验, 对比研究了裸TFBG和镀金TFBG传感器对溶液折射率的传感特性。 从而验证了模拟仿真得出的结论并定量分析得知: 镀金后具有表面等离子体共振的TFBG溶液折射率灵敏度大于500 nm·RIU-1, 而裸TFBG为2 nm·RIU-1左右, 大约提高了200～300倍, 且在一定范围内中心波长与溶液折射率的线性拟合度都在0.99以上。

为了突破现存的倾斜布拉格光纤光栅制作方法的局限,提出了采用非对称光路制作倾斜条纹反射式光纤光栅的方法。该方法是通过在全息光路中加入柱面镜,将圆形光斑聚焦成线状激光,线状激光以平行于材料层的方式写入,从而获得不同倾斜角度,条纹间距任意的倾斜光纤光栅。通过写入条件的控制,达到精确控制光栅的反射率和带宽的目的。模拟仿真和分析表明这种方法对实际制作倾斜光纤光栅具有一定的参考意义和实用价值。