Chirality plays an important role in biological processes, and enantiomers often possess similar physical properties and different physiological functions. Thus, chiral detection of enantiomers has become a hot topic in recent years, and methods to enhance chiral molecular recognition are in urgent demand. In this work, a polarization detection method was used for different chiral drugs based on a specially designed metasurface composed of asymmetric double-opened rings and the surface enhancement effect of gold nanoparticles (GNPs). The experiment results show that the frequency shifts caused by the nearfield interaction of the metasurface and biomolecules have been significantly improved by GNPs, and both the limit of detection and detection precision of the metasurface can reach the 10⁻⁵ g ml⁻¹ level. Moreover, the polarization sensing characterized by right circular polarization (RCP), the polarization elliptical angle (PEA), and the polarization rotation angle (PRA) shows that the enantiomers of three drugs can be distinguished, especially using the PEA spectrum; the maximum difference between enantiomers is over 30° with a precision of 6.6 × 10⁻⁷ g mL⁻¹. Our THz polarization sensing and the GNP enhancement method inspire an efficient strategy for the highly sensitive detection of enantiomers.

A terahertz (THz) all-dielectric metasurface with crescent cylinder arrays for chiral drug sensing has been demonstrated. Through the multipole expansion method, we theoretically found that breaking the symmetry of the metasurface can excite higher-order resonance modes and provide stronger anisotropy as well as enhanced sensitivity for the surroundings, which gives a better sensing performance than lower-order resonance. Based on the frequency shift and transmittance at higher-order resonance, we carried out the sensing experiments on (R)-(−)-ibuprofen and (S)-(+)-ibuprofen solution on the surface of this metasurface sensor. We were able to monitor the concentrations of ibuprofen solutions, and the maximum sensitivity reached 60.42 GHz/mg. Furthermore, we successfully distinguished different chiral molecules such as (R)-(−)-ibuprofen and (S)-(+)-ibuprofen in the 5 μL trace amount of samples. The maximum differentiation was 18.75 GHz/mg. Our analysis confirms the applicability of this crescent all-dielectric metasurface to enhanced sensing and detection of chiral molecules, which provides new paths for the identification of biomolecules in a trace amount.

Metasurface-based terahertz (THz) biosensors have attracted significant attention in the biological field due to their non-destructive and harmless interaction with biochemical samples. However, it is still challenging for specific detection in mixed samples via THz metasensors. In this work, we modified THz metasurface chips and target biomolecules respectively, utilized immune binding and gold nanorods (GNRs), and achieved THz high-sensitive specific detection for Alzheimer’s marker Aβ _1-42 protein via a microfluidic platform. A double-ring coupled metallic metasurface that can provide a strong localized field enhancement was fabricated, then modified with Aβ _1-42 -antibody by covalent binding to capture Aβ _1-42 . Moreover, GNRs were introduced to bind Aβ _1-42 , and the sensor’s response to Aβ _1-42 is greatly enhanced. Through this sensor-analytes modification, the sensitivity of the sensor can reach 240.91 GHz·ml/nmol, and the limit of detection (LoD) is one order of magnitude higher than that without GNRs. In addition, the LoD for Aβ _1-42 reached 0.2 pmol/mL (1 ng/mL), which is 100 times higher than other nonspecific proteins. More importantly, the biosensor can also recognize Aβ _1-42 in a mixed sample with physiological limiting concentration. Our high selectivity and sensitivity nanomaterial-metasurface hybrid-based THz biosensor would give access to rich applications in label-free biosensing.

Terahertz (THz) communication and sensing technology has recently gained increasing attention. Metallic parallel-plate waveguides (PPWG) have been researched since they were proven to be the carrier of lossless transmission of THz waves. However, previous reports have focused on the transmission and phase properties of single-polarized THz waves in PPWGs and have barely investigated the polarization properties. To reconstruct the polarization of the output THz wave in a PPWG, we study the transmission and phase properties of both TE and TM modes in detail. The phase difference of the TE and TM modes can be continuously adjusted by varying the propagation length and the gap of the two plates in PPWG due to the different dispersion of the two modes. The polarization ellipticity and rotation angle can be modulated in the range of ±45°. When a photonic cavity structure is applied to a PPWG, the output wave will be converted to 90° linear polarization at the frequency located in the cavity mode. All the proposed polarization control can be tuned by changing the structural parameters forming the PPWGs, making this approach attractive for integrating the function of the THz waveguides, which has significance for THz communication and sensing.