Polarization-Independent Terahertz Surface Plasmon Resonance Biosensor for Species Identification of Panax and Paeonia

In this paper, we proposed a polarization-independent terahertz surface plasmon resonance (SPR) biosensor based on an angular cyclic element structure. The biosensor has the advantages of high sensitivity detection and high stability against the polarization change of incident terahertz light. Based on the principle that the spatial longitudinal electric field of the SPR biosensor is nonlinear and sensitive to the dielectric constant of the sample, we theoretically proved that specific nonlinear response curves with certain saturating speed and amplitude can be formed to identify different samples. The biosensor was applied to identify Panax (notoginseng, ginseng and American ginseng, 48 samples each) and Paeonia (white peony and red peony, 48 samples each) with the accuracy of 95.8% and 94.4%, respectively. The standard deviations (SD) were less than 0.347% and 0.403%, respectively. Therefore, the polarization-independent terahertz biosensor can rapidly and accurately identify Panax species and Paeonia species. These results provide a new reference for rapid and low-cost identification of medicine species.