Department of Electrooptics and Photonics Engineering and The Ilse Katz Institute for Nanoscale Science and Technology, Ben Gurion University of the Negev, Beer Sheva 84105, Israel.
CBMN, UMR 5248 CNRS, Université de Bordeaux, Allée Geoffroy St. Hilaire, 33600 Pessac, France.
Sensors (Basel). 2019 Mar 21;19(6):1402. doi: 10.3390/s19061402.
Plasmon waveguide resonance (PWR) sensors exhibit narrow resonances at the two orthogonal polarizations, transverse electric (TE) and transverse magnetic (TM), which are narrower by almost an order of a magnitude than the standard surface plasmon resonance (SPR), and thus the figure of merit is enhanced. This fact is useful for measuring optical anisotropy of materials on the surface and determining the orientation of molecules with high resolution. Using the diverging beam approach and a liquid crystal retarder, we present experimental results by simultaneous detection of TE and TM polarized resonances as well as using fast higher contrast serial detection with a variable liquid crystal retarder. While simultaneous detection makes the system simpler, a serial one has the advantage of obtaining a larger contrast of the resonances and thus an improved signal-to-noise ratio. Although the sensitivity of the PWR resonances is smaller than the standard SPR, the angular width is much smaller, and thus the figure of merit is improved. When the measurement methodology has a high enough angular resolution, as is the one presented here, the PWR becomes advantageous over other SPR modes. The possibility of carrying out exact numerical simulations for anisotropic molecules using the 4 × 4 matrix approach brings another advantage of the PWR over SPR on the possibility of extracting the orientation of molecules adsorbed to the surface. High sensitivity of the TE and TM signals to the anisotropic molecules orientation is found here, and comparison to the experimental data allowed detection of the orientation of lipids on the sensor surface. The molecular orientations cannot be fully determined from the TM polarization alone as in standard SPR, which underlines the additional advantage of the PWR technique.
等离子体导波共振（PWR）传感器在两个正交偏振方向上表现出窄的共振，即横电（TE）和横磁（TM），其宽度比标准表面等离子体共振（SPR）窄约一个数量级，因此品质因数得到了提高。这一事实对于测量表面材料的光学各向异性和确定分子的取向具有重要意义。我们使用发散光束方法和液晶延迟器，通过同时检测 TE 和 TM 偏振共振，以及使用带有可变液晶延迟器的快速高对比度串行检测，展示了实验结果。虽然同时检测使系统更简单，但串行检测具有获得更大共振对比度的优点，从而提高了信噪比。虽然 PWR 共振的灵敏度比标准 SPR 小，但角度宽度小得多，因此品质因数得到了提高。当测量方法具有足够高的角度分辨率时，如本文所提出的那样，PWR 比其他 SPR 模式更具优势。使用 4×4 矩阵方法对各向异性分子进行精确数值模拟的可能性为 PWR 相对于 SPR 带来了另一个优势，即有可能提取吸附在表面上的分子的取向。我们发现 TE 和 TM 信号对各向异性分子取向的灵敏度很高，并且与实验数据的比较允许检测传感器表面上脂质的取向。与标准 SPR 一样，不能仅从 TM 偏振 alone 完全确定分子取向，这突出了 PWR 技术的额外优势。
