Analogue of electromagnetically induced transparency in a metal-dielectric bilayer terahertz metamaterial

Electrostatic enhanced terahertz metamaterial biosensing via gold nanoparticles integrated with biomolecules

Terahertz spectroscopy has drawn great interest for the detection and characterization of biological matter, but its limited sensitivity to biomolecules with weak changes in dielectric properties with varying concentration has hinders potential bio-sensing applications. Here, a novel terahertz sensor was developed for enhancing the ability to detect biomolecules based on two electromagnetically induced transparency (EIT) metamaterials coupled with gold nanoparticles (AuNPs) integrated with biomolecules. The electrostatic interaction between AuNPs and positively charged biomolecules generates localized field enhancement at the biomolecule-metamaterial interface, resulting in a threefold increase in sensitivity for positively charged histidine that exhibit weak dielectric property changes with varying concentration. As a contrast, glucose shows a weaker effect due to its electrostatically neutral nature. Experimental studies reveal that by evaluating the modulation depth (MD) and modulation enhancement (ME) factors of the transmission peak for histidine and glucose in the presence of AuNPs, we achieve and enhance intuitive detection and discrimination of these biomolecules. Additionally, a two-EIT metamaterial with a 1 × 2 pixel array enables multiparameter imaging, visualizing the concentration and spatial distribution of biomolecules. Our results not only significantly improve the response sensitivity of biomolecules with weak dielectric properties in the terahertz domain, but also provide a new idea for developing high-sensitivity functionalized terahertz biosensors and advancing multi-biomolecular analysis and imaging techniques.

Exploring the Application of Multi-Resonant Bands Terahertz Metamaterials in the Field of Carbohydrate Films Sensing

Terahertz spectroscopy is a powerful tool for investigating the properties and states of biological matter. Here, a systematic investigation of the interaction of THz wave with "bright mode" resonators and "dark mode" resonators has been conducted, and a simple general principle of obtaining multiple resonant bands has been developed. By manipulating the number and positions of bright mode and dark mode resonant elements in metamaterials, we realized multi-resonant bands terahertz metamaterial structures with three electromagnetic-induced transparency in four-frequency bands. Different carbohydrates in the state of dried films were selected for detection, and the results showed that the multi-resonant bands metamaterial have high response sensitivity at the resonance frequency similar to the characteristic frequency of the biomolecule. Furthermore, by increasing the biomolecule mass in a specific frequency band, the frequency shift in glucose was found to be larger than that of maltose. The frequency shift in glucose in the fourth frequency band is larger than that of the second band, whereas maltose exhibits an opposing trend, thus enabling recognition of maltose and glucose. Our findings provide new insights into the design of functional multi-resonant bands metamaterials, as well as new strategies for developing multi-band metamaterial biosensing devices.

Tailoring dual-band electromagnetically induced transparency with polarization conversions in a dielectric-metal hybrid metastructure

Metastructure analogs of electromagnetically induced transparency (EIT) provide a new approach for engineering realizations of nonlinear optical manipulations regardless of harsh conditions; further can be employed in polarization conversions for its low-loss transmission and phase modulation. In this work, dual-band EIT in a dielectric-metal hybrid metasurface achieved via providing different coupling channels is theoretically investigated with a maximum group delay of 404 ps. The linear-to-circular polarization conversion (LCPC) behaviors are observed respectively holding the transmittance of 0.58 at 0.68 THz, 0.73 at 0.76 THz, 0.61 at 0.90 THz, 0.53 at 0.99 THz, owning to the asymmetric EIT responses in the transverse magnetic (TM) and transverse electric (TE) modes incidence. On the other hand, phase-transition VO₂ is doped to perturb the dark mode resonances. With its conductivity σ = 10⁵ S/m, dual transparency peaks transform into unimodal broadband transmission windows with relative bandwidths of 17.1% and 9.1% under the TE and TM excitations apart. Induced LCPC possesses a bandwidth of 10.4% centered at 0.76 THz attributed to the drastic dispersion. The as-proposed design exploits pattern asymmetry of EIT responses to realize LCPC, promising the wide prospect of reconfigurable multiplexings.

Electromagnetically induced transparency-based metal dielectric metamaterial and its terahertz sensing application

In this paper, electromagnetically induced transparency has been reported in the metal-dielectric structure that provides the platform for high-quality factor Fano resonance in the terahertz region. The electric dipole in the metal ring provides a bright mode, while the electric and magnetic dipoles formed in the dielectric offer bright and dark modes, respectively. Two resonance dips have been obtained with a high-quality factor of 89.5 and 23 leads to a high figure of merit of sensor equal to 6 and 4 for the first and second resonance dips, respectively, which is useful for the design and development of metamaterial-based sensing devices and biosensors.

Analogue of Electromagnetically Induced Transparency in an All-Dielectric Double-Layer Metasurface Based on Bound States in the Continuum

Bound states in the continuum (BICs) have attracted much attention due to their infinite Q factor. However, the realization of the analogue of electromagnetically induced transparency (EIT) by near-field coupling with a dark BIC in metasurfaces remains challenging. Here, we propose and numerically demonstrate the realization of a high-quality factor EIT by the coupling of a bright electric dipole resonance and a dark toroidal dipole BIC in an all-dielectric double-layer metasurface. Thanks to the designed unique one-dimensional (D)-two-dimensional (2D) combination of the double-layer metasurface, the sensitivity of the EIT to the relative displacement between the two layer-structures is greatly reduced. Moreover, several designs for widely tunable EIT are proposed and discussed. We believe the proposed double-layer metasurface opens a new avenue for implementing BIC-based EIT with potential applications in filtering, sensing and other photonic devices.