Scientists propose a new biosensor design for more accurate medical diagnostics

Scientists from ITMO University, together with colleagues from Russia and China, have proposed a new design for an ultrasensitive terahertz sensor. It is designed to confine terahertz radiation within the structure and enhance its interaction with matter. According to calculations, the system could detect changes in the composition of liquid media with high accuracy without the use of chemical reagents. In the future, the technology could be useful for medical diagnostics, environmental monitoring, and industrial quality control. The findings, supported by a grant from the Russian Science Foundation, were published in the journal Nanophotonics.

Terahertz radiation is a promising tool for medical diagnostics and environmental monitoring, Nauka Rossii reports. It is safe for humans, can penetrate opaque materials, and can interact with the vibrations of large organic molecules. However, existing terahertz sensors have several limitations: low sensitivity, which prevents them from detecting small changes in the concentration of a substance, and low selectivity, which makes it difficult for sensors to distinguish between different types of molecules. This is because the wavelength of terahertz radiation is several times larger than the size of molecules: the wave effectively “does not notice” the particle, resulting in very weak interaction between light and matter.

Scientists from ITMO University, the A.F. Ioffe Institute of Physics and Technology, and Harbin Institute of Technology in China have proposed a terahertz sensor design capable of “trapping” light inside the structure and thereby increasing the strength of its interaction with matter. The system consists of a metasurface made of graphene strips, a microresonator, and a gold reflective layer. Together, they create conditions in which terahertz radiation is barely reflected from the structure and its energy is efficiently concentrated inside the microresonator, where the substance being analyzed is located.

When the structure is illuminated with a terahertz wave, a special phenomenon known as a Fano resonance occurs, characterized by an asymmetric absorption line shape. As a result, the system enhances the interaction between light and matter: external radiation leakage is balanced by internal losses, reflection drops almost to zero, and absorption reaches its maximum. The light is neither reflected nor scattered — it is completely absorbed by the substance being analyzed as it passes repeatedly through the sensor structure.

Another advantage of the proposed system is the ability to tune it electrically. By changing the voltage applied to the graphene metasurface, researchers can control the resonance parameters and adjust the sensor’s operation to different conditions while maintaining its high sensitivity.

The authors plan to manufacture a physical sensor and adapt the platform for identifying chiral molecules — compounds that exist in two mirror-image forms. Although their chemical composition is identical, these forms can interact differently with the body: one may have a therapeutic effect, while the other may be ineffective or even toxic. The ability to distinguish between them is therefore particularly important in pharmacology.

“We expect that the sensor design we have proposed will make it possible to create a device that is several times more sensitive to changes in the composition of a medium than existing analogues. Such a device would respond to even the slightest shifts in the refractive index — for example, to the presence of trace amounts of glucose molecules, proteins, viruses, or toxins in a liquid,” said Mikhail Rybin, one of the study’s authors and a leading researcher at ITMO University’s New PhysTech.

The development of such sensors could be useful for detecting cancer cells and viruses directly in biopsy samples without staining biological material or requiring complex preparation; identifying trace amounts of pesticides, herbicides, or industrial pollutants in water; and quality control in the pharmaceutical and food industries when analyzing liquid media.

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