Metasurface biosensing confronts a significant challenge in simultaneously achieving broadband response, high quality-factor (Q-factor), and ultrahigh sensitivity for specific trace-analyte detection at terahertz (THz) frequencies. Recently, quasi-bound states in the continuum (QBICs) metasurfaces provided enhanced light–matter interactions and ultrahigh sensitivity in narrow resonant bands. In this work, an angle-scanning QBIC metasurface array pixelated with just 5 × 5 scaling units is proposed to achieve an ultra-broad spectrum from 1 to 2.8 THz for fingerprint bio-detection. The symmetry-protected QBIC is excited by breaking the symmetry of copper block dimer resonator structures, achieving a Q-factor of 20 and a sensitivity of 500 GHz/RIU. A spectral step of approximately 10 GHz is demonstrated in this approach, and glutamic acid and glutamine are specifically detected, with detection limits reaching 15.4 μg/cm² and 14.7 μg/cm². This design provides a novel approach for achieving ultra-wideband, specific, and highly sensitive detection. This capability offers an efficient strategy for monitoring tumor metabolic biomarkers and paves the way for applications in early diagnosis and advanced broadband THz detection.

Terahertz (THz) biosensing faces critical challenges in balancing high sensitivity and broadband spectral coverage, particularly under miniaturized device constraints. Conventional quasi-bound states in the continuum (QBIC) metasurfaces achieve high quality factor (Q) but suffer from narrow bandwidth, while angle-scanning strategies for broadband detection require complex large-angle illumination. Here, we propose a symmetry-engineered, all-dielectric metasurface that leverages multipolar interference coupling to overcome this limitation. By introducing angular perturbation, the metasurface transforms the original magnetic dipole (MD)-dominated QBIC resonance into hybridized, multipolar modes. It arises from the interference coupling between MD, toroidal dipole (TD), and magnetic quadrupole (MQ). This mechanism induces dual counter-directional, frequency-shifted, resonance branches within angular variations below 16°, achieving simultaneous 0.42 THz broadband coverage and high Q of 499. Furthermore, a derived analytical model based on Maxwell equations and mode coupling theory rigorously validates the linear relationship between frequency splitting interval and incident angle with the Relative Root Mean Square Error (RRMSE) of 1.4% and the coefficient of determination ($R^2$) of 0.99. This work establishes a paradigm for miniaturized THz biosensors, advancing applications in practical molecular diagnostics and multi-analyte screening.

Terahertz (THz) spectroscopy, an advanced label-free sensing method, offers significant potential for biomolecular detection and quantitative analysis in biological samples. Although broadband fingerprint enhancement compensates for limitations in detection capability and sensitivity, the complex optical path design in operation restricts its broader adoption. This paper proposes a multi-degree-of-freedom stretchable metasurface that supports magnetic dipole resonance to enhance the broadband THz fingerprint detection of trace analytes. The metasurface substrate and unit cell structures are constructed using polydimethylsiloxane. By adjusting the sensor’s geometric dimensions or varying the incident angle within a narrow range, the practical optical path is significantly simplified. Simultaneously, the resonance frequency of the transmission curve is tuned, achieving high sensitivity for effectively detecting cinnamoylglycine. The results demonstrate that the metasurface achieves a high-quality factor of 770.6 and an excellent figure of merit of 777.2, significantly enhancing the THz sensing capability. Consequently, the detection sensitivity for cinnamoylglycine can reach 24.6 µg·cm⁻². This study offers critical foundations for applying THz technology to biomedical fields, particularly detecting urinary biomarkers for diseases like gestational diabetes.

THz waves have garnered significant attention across multiple domains, particularly in high-sensitivity sensing applications. Metamaterials are applicable in THz sensors owing to their exceptional sensitivity, particularly in refractive index measurement and pesticide identification. This paper proposes a THz metamaterial sensor for detecting ether kresoxim-methyl. The sensor comprises a periodic array of silicon cylindrical trimers organized on a silicon substrate. Resonances in the guided mode, dictated by bound states in the continuum spectrum, can be stimulated by meticulously configuring the geometric arrangement of the silicon column trimer. The sensor demonstrates a Q-value of up to 143 at the resonant frequency. The detection of pesticide residues achieved high sensitivity and specificity, with a detection limit of 37.74 μg/cm². This study presents a novel alternative for THz metamaterial sensors characterized by high sensitivity and a broad spectrum of pesticide concentration detection. The sensor platform developed in this paper, utilizing conventional CMOS technology, is posited as a potential detection instrument for herbicide and pesticide residues in agriculture and food.

Terahertz (THz) metasurface biosensors still encounter difficulties in simultaneously achieving high spectral resolution and stable readout across different refractive-index regimes. In this work, an all-liquid-crystal-polymer (LCP) THz metasensor supporting dual quasi-bound states in the continuum (quasi-BIC) resonances is proposed for regime-dependent refractive-index sensing. By introducing structural asymmetry into a periodic LCP cubic-cluster metasurface, two pronounced resonances are generated with quality factors (Q factors) of 6811 and 2526, respectively. Near-field distributions and multipole decomposition analysis indicate that the two resonances possess distinct electromagnetic features, which result in different responses to surrounding dielectric perturbations. In the low-refractive-index range of 1.0–1.5, the two resonance frequencies exhibit a linear variation with refractive index, yielding sensitivities of 122 GHz/RIU and 179 GHz/RIU, respectively. These dual-mode linear responses further offer a foundation for concentration- and temperature-related evaluation through analyte refractive-index mapping. In the higher-refractive-index range of 1.5–1.8, the intermodal frequency difference shows improved linearity with refractive index compared with the individual resonance frequencies, enabling a differential readout scheme with enhanced robustness against common perturbations. The results demonstrate that the proposed all-LCP dual-quasi-BIC metasensor not only enables high-resolution THz refractive-index sensing, but also establishes a regime-dependent spectral readout approach for different dielectric-response intervals.

Terahertz (THz) fingerprint detection is central to identifying characteristic absorption fingerprints of biomolecules derived from their intrinsic rotational and vibrational modes. The development of guided-mode resonance (GMR) technology together with pixelated design offers a new approach to enhance the recognition capability of such fingerprint spectra. Here, a novel secondary grating metasurface based on cycloolefin polymer (COP) is proposed, which adopts an ultra-minimalist dual-pixel complementary architecture to excite high-quality (Q)-factor GMR. Its spectral resolution does not exceed 50 GHz, enabling precise capture of target molecular characteristic information and meeting the requirements of broadband fingerprint sensing. More importantly, the design regulates the dual-pixel grating units through parameter gradient optimization and incorporates a dual regulation mode of static pixel-targeted coverage and dynamic angle fine tuning. By adjusting geometric parameters and incident angles, broadband coverage from 1.15 THz to 2.20 THz is achieved, which can accurately match the multi-fingerprint detection requirements of glutamic acid (Glu) and glutamine (Gln). This metasurface sensor, integrating the advantages of pixelation and high-Q-factor GMR characteristics, provides an effective strategy for enhanced broadband THz fingerprint sensing and shows broad application potential in the field of biochemical trace detection.