Kaňok Roman, Ciprian Dalibor, Hlubina Petr
Department of Physics, Technical University Ostrava, 17. listopadu 2172/15, 708 00 Ostrava-Poruba, Czech Republic.
Sensors (Basel). 2020 Mar 13;20(6):1616. doi: 10.3390/s20061616.
Spatial phase modulation in an imaging interferometer is utilized in surface plasmon resonance (SPR) based sensing of liquid analytes. In the interferometer, a collimated light beam from a laser diode irradiating at 637.1 nm is passing through a polarizer and is reflected from a plasmonic structure of SF10/Cr/Au attached to a prism in the Kretschmann configuration. The beam passes through a combination of a Wollaston prism, a polarizer and a lens, and forms an interference pattern on a CCD sensor of a color camera. Interference patterns obtained for different liquid analytes are acquired and transferred to the computer for data processing. The sensing concept is based on the detection of a refractive index change, which is transformed via the SPR phenomenon into an interference fringe phase shift. By calculating the phase shift for the plasmonic structure of SF10/Cr/Au of known parameters we demonstrate that this technique can detect different weight concentrations of ethanol diluted in water, or equivalently, different changes in the refractive index. The sensitivity to the refractive index and the detection limit obtained are -278 rad/refractive-index-unit (RIU) and 3.6 × 10 - 6 RIU, respectively. The technique is demonstrated in experiments with the same liquid analytes as in the theory. Applying an original approach in retrieving the fringe phase shift, we revealed good agreement between experiment and theory, and the measured sensitivity to the refractive index and the detection limit reached -226 rad/RIU and 4.4 × 10 - 6 RIU, respectively. These results suggest that the SPR interferometer with the detection of a fringe phase shift is particularly useful in applications that require measuring refractive index changes with high sensitivity.
成像干涉仪中的空间相位调制被用于基于表面等离子体共振（SPR）的液体分析物传感。在干涉仪中，来自激光二极管的准直光束以637.1nm波长照射，穿过一个偏振器，并从附着在Kretschmann结构棱镜上的SF10/Cr/Au等离子体结构反射。该光束穿过沃拉斯顿棱镜、偏振器和透镜的组合，并在彩色相机的CCD传感器上形成干涉图案。获取不同液体分析物的干涉图案并传输到计算机进行数据处理。传感概念基于对折射率变化的检测，该变化通过SPR现象转化为干涉条纹的相移。通过计算已知参数的SF10/Cr/Au等离子体结构的相移，我们证明了该技术可以检测水中稀释的不同重量浓度的乙醇，或者等效地检测不同的折射率变化。所获得的对折射率的灵敏度和检测限分别为-278 rad/折射率单位（RIU）和3.6×10 - 6 RIU。在与理论中相同的液体分析物的实验中演示了该技术。应用一种原始方法来检索条纹相移，我们发现实验与理论之间具有良好的一致性，并且测量得到的对折射率的灵敏度和检测限分别达到-226 rad/RIU和4.4×10 - 6 RIU。这些结果表明，检测条纹相移的SPR干涉仪在需要高灵敏度测量折射率变化的应用中特别有用。
