Biosensors based on terahertz (THz) metasurfaces have recently attracted widespread attention. However, few have been reported so far because it is a challenge to achieve ultrasensitive multidimensional detection in the THz spectrum. Here, we propose a novel THz biosensor that consists of a metasurfaces and a metal oxide semiconductor‐like structure (MOSLS), which is based on patterned graphene–polyimide–perovskite. We varied the photoconductivity of the MOSLS via the electrostatic doping effect. The biosensor could detect whey protein down to a concentration limit of 6.25 ng/mL. Significant responses in frequency, phase, and transmission amplitude were all detected for different protein concentrations. The transmission value difference, frequency shift, and phase difference increased with the concentration of whey protein, clearly demonstrating multidimensional biosensing. Moreover, by applying lasers with different wavelengths, we have realized reversible biosensing in THz region for the first time. These results are very promising for applications of THz metasurfaces in the field of biosensing.

Integrating novel materials is critical for the ultrasensitive, multi-dimensional detection of biomolecules in the terahertz (THz) range. Few studies on THz biosensors have used semiconductive active layers with tunable energy band structures. In this study, we demonstrate three THz biosensors for detecting casein molecules based on the hybridization of the metasurface with graphitic carbon nitride, graphene, and heterojunction. We achieved low-concentration detection of casein molecules with a 3.54 ng/mL limit and multi-dimensional sensing by observing three degrees of variations (frequency shift, transmission difference, and phase difference). The favorable effect of casein on the conductivity of the semiconductive active layer can be used to explain the internal sensing mechanism. The incorporation of protein molecules changes the carrier concentration on the surface of the semiconductor active layer via the electrostatic doping effect as the concentration of positively charged casein grows, which alters the energy band structure and the conductivity of the active layer. The measured results indicate that any casein concentration can be distinguished directly by observing variations in resonance frequency, transmission value, and phase difference. With the heterojunction, the biosensor showed the highest response to the protein among the three biosensors. The Silvaco Atlas package was used to simulate the three samples’ energy band structure and carrier transport to demonstrate the benefits of the heterojunction for the sensor. The simulation results validated our proposed theoretical mechanism model. Our proposed biosensors could provide a novel approach for THz metasurface-based ultrasensitive biosensing technologies.

Active control of the electromagnetically induced transparency (EIT) analog is desirable in photonics development. Here, we theoretically and experimentally proposed a novel terahertz (THz) asymmetric metasurface structure that can possess high-sensitivity modulation under extremely low power density by integrating perovskite or graphene. Using the novel metasurface structure with the perovskite coating, the maximum amplitude modulation depth (AMD) of this perovskite-based device reached 490.53% at a low power density of 12.8037 mW / cm 2 . In addition, after the novel THz metasurface structure was combined with graphene, this graphene-based device also achieved high AMD with the maximum AMD being 180.56% at 16.312 mW / cm 2 , and its transmission amplitude could be electrically driven at a low bias voltage. The physical origin of this modulation was explained using a two-oscillator EIT model. This work provides a promising platform for developing high-sensitivity THz sensors, light modulators, and switches.

Food safety is an important consideration for the food industry and for daily life, and food additives are essential in the modern food industry. Graphene-based metamaterial sensors are of great value and have potential applications in the detection of food additives, due to their ultra-sensitivity. This paper proposes a metasurface sensor consisting of graphene and dual elliptical ring resonators (Gr-DERRs) sensor for the detection of two common food additives. The limit of detection (LOD) for Sudan I solution is 581.43 fg/ml and, for taurine, 52.86 fg/ml. This ultra-sensitive detection is achieved by exploiting the unique electromagnetic properties of electromagnetically induced transparency (EIT) resonance, together with the Fermi energy level of graphene moving to the Dirac point, resulting in a dramatic change in the dielectric environment. The Gr-DERRs sensor has brings significant improvement in the detection of food additives with detection limits reduced to the femtogram level.

The combined application of metasurface and terahertz (THz) time-domain spectroscopy techniques has received considerable attention in the fields of sensing and detection. However, to detect trace samples, the THz wave must still be enhanced locally using certain methods to improve the detection sensitivity. In this study, we proposed and experimentally demonstrated a fano resonance metasurface-based silver nanoparticles (FaMs-AgNPs) sensor. AgNPs can enhance the sensitivity of the sensor by generating charge accumulation and inducing localized electric field enhancement through the tip effect, thereby enhancing the interaction between the THz waves and analytes. We investigated the effects of four different contents of AgNPs, 10 µl, 20 µl, 30 µl and 40 µl, on the detection of acetamiprid. At 30 µl of AgNPs, the amplitude change of the FaMs-AgNPs sensor was more pronounced and the sensitivity was higher, which could detect acetamiprid solutions as low as 100 pg/ml. The FaMs-AgNPs sensor has the advantages of a simple structure, easy processing, and excellent sensing performance, and has a great potential application value in the field of THz trace detection and other fields.