Ultrasensitive Terahertz Biodetection Using Metasensors Based on Parity-Time Symmetry

Terahertz (THz) spectroscopy has unique sensing capabilities for biological cells due to its high temporal resolution and label-free characteristics. By combining THz technologies with the local enhancement effects of the electric field induced by the metasurface, high sensitivity detection of biological analytes can be achieved. In this article, an ultrasensitive THz metasurface biosensor based on parity-time (PT) symmetry is proposed. Consisting of a cut wire and a pair of split ring resonators, the exceptional point (EP) structure in PT symmetry can realize a balance between the gain and the loss, which leads to a high detection sensitivity. The simulation shows that the proposed biosensor can reach a sensitivity as high as 584 GHz/RIU at the EP with polarization-insensitive stability across a ±35° angle range. Experimentally, the biosensor achieves a sensitivity up to 1030.51 kHz/ (cell/mL⁻¹) in detecting different biological cells. Principal component analysis is used to reduce the dimensionality of features composed of frequency shifts and peak amplitudes. A random forest model is then used to classify the processed features and achieves a 98.9% identification accuracy. The proposed biosensor demonstrates capabilities of highly sensitive detection of cancer cells, providing an effective and rapid method for early cancer screening, grading, and staging.