A concentric square ring terahertz metamaterial sensor for highly sensitive detection of cytosine methylation.

Terahertz metasurfaces provide an effective platform for terahertz sensing because they allow flexible control of subwavelength resonances and strong electromagnetic field confinement. In this work, a concentric square ring terahertz metasurface sensor is designed and fabricated to support an electromagnetically induced transparency (EIT) resonance, which originates from interference between radiative bright modes and subradiant dark modes in the metasurface structure. The formation of the EIT resonance leads to sharp transmission features, strong dispersion, and highly localized electric fields near the resonant elements, which greatly enhance the interaction between terahertz waves and changes in the surrounding dielectric environment. Based on this mechanism, the metasurface exhibits high sensing sensitivity and good robustness. A maximum refractive index sensitivity of 283 GHz/RIUis achieved, together with a detection limit of 0.01 mg/mL. At the same time, the sensing response remains stable under substrate loss, fabrication imperfections, and variations in background dielectric properties, indicating reliable performance under practical conditions. To experimentally verify the sensing capability, cytosine and its methylated form are selected as representative analytes and deposited on the metasurface surface. Distinct frequency shifts and amplitude changes are observed in the transmission spectra, which allow clear discrimination between the two molecules. This discrimination can still be achieved in a DNA environment, demonstrating strong anti-interference capability of the sensor. The results show that the sensing performance mainly arises from EIT-enhanced field confinement and the resulting modulation of the local electromagnetic response, rather than from analyte-specific chemical functionalization. Overall, this work demonstrates that EIT-based terahertz metasurfaces can serve as a sensitive and robust sensing platform for label-free detection of small dielectric perturbations, and it provides a general physical strategy for terahertz sensing applications involving complex environments.