A research team has developed a sensor operating in the terahertz (THz) band that exploits parity-time (PT) symmetry to boost the detection of frozen oral cancer tissues. The technique aims to overcome the usual limitations of THz imaging in biological samples, where the contrast between healthy and tumour tissue is often weak and freezing conditions alter the optical response of the material.

The terahertz band occupies the region of the electromagnetic spectrum between microwaves and near-infrared light, and is particularly sensitive to water content and soft-tissue structure, which makes it attractive for stain-free histology. However, the signal returned by frozen tissue is faint and noisy, making it difficult to reliably distinguish tumour from surrounding tissue during the preparation of surgical sections.

Parity-time symmetry originates in the physics of open systems with balanced gain and loss. In a PT-symmetric resonator, two coupled modes — one with gain and one with loss — can merge at an exceptional point, where the system's response becomes exquisitely sensitive to small perturbations of its environment. That sensitivity is precisely what is transferred here to detection: when the frozen tissue couples to the sensor, the resonance shift is amplified and the contrast improves compared with the conventional configuration.

The result is a device able to distinguish more sharply the regions affected by oral cancer in frozen samples, a common scenario in oncological surgery, where intraoperative tissue analysis demands speed and precision. The contrast enhancement via exceptional points paves the way for more compact and reliable THz sensors for rapid pathology, although validation in large patient cohorts and integration into the surgical workflow remain pending steps.