Actively controlling the amplitude and phase of terahertz (THz) wave is of great significance for THz broadband wireless communication and high-resolution THz imaging. In this paper, we present a THz amplitude and phase modulator based on electrically triggered vanadium dioxide (VO ₂ ) reconfigurable metasurface. The unit cell of the device consists of three concentric split-rings-rings (SRRs) on the sapphire substrate, i.e., one VO ₂ -split-ring (VSR) and two metal SRRs. The VSR is embedded between two metal SRRs. The resonance mode, resonance intensity and surface current distribution in the unit cell can be dynamically manipulated by electrically triggering the insulator-to-metal-transition (IMT) of the VO ₂ . The sample is fabricated using a surface micromachining process and characterized by a THz time-domain-spectroscopy (TDS) system. The experimental results show that, 90 degrees phase shift is achieved in a broad bandwidth of 70 GHz. Meanwhile, the amplitude modulation depth reaches 71% at 0.79 THz. The transmission and the phase shift are calculated by an equivalent circuit model, and simultaneously simulated using a full-wave circuit simulation software based on the Method of Moments (MoM). The calculation and simulation results agree with the experimental results. The device has potential applications in THz imaging, broadband wireless communications and array phase controlling.

A novel strategy for screening early hepatocellular carcinoma (HCC) using a terahertz (THz) metamaterials (MMs) biosensor modified with the antibody against Alpha-Fetoprotein (AFP) is proposed. The designed biosensor consists of split-resonant-rings (SRRs) with double resonant frequencies that are optimized using the finite integration time domain (FITD) method and manufactured by a surface micromachining process. The experimental results indicate that the HCC biomarker AFP could be accurately distinguished with a concentration as low as 0.1 ng/ml via analyzing the shifts of double resonant frequencies. Meanwhile, specific detection of AFP-antigen in solution and HCC serum has been achieved through the antigen-antibody specific binding. These results demonstrate the sensitivity and specificity of THz MMs biosensor for molecular detection of trace cancer biomarkers in biochemical sensing. Furthermore, the sensitivity of specific cancer biomarkers can be further improved by optimizing the metamaterial structure and applying the double resonant frequencies. Therefore, this approach may own great potential for special identification of early cancer molecules.

Squamous cell carcinoma antigen (SCCA) level is an auxiliary indicator for lung cancer diagnosis and predictive monitoring, and its standard reference value is less than 1.5 ng/mL. Therefore, achieving high sensitivity and specific detection of the SCCA is a challenge. In this work, we designed a double split-ring-resonator (SRR) terahertz (THz) metasurface sensor. Simulation results show that the sensitivity of the sensor can reach 103 GHz/RIU (refractive index unit). After the sensor is modified with different concentrations of halloysite-nanotubes (HNTs), the resonant frequency of the sensor exhibits different linear responses to different concentrations of SCCA. The optimum concentration of HNTs to enhance the detection performance of the sensor was obtained as 10 mg/mL. The linear range of SCCA concentration of the HNTs modified sensor was 1 pg/mL-100 ng/mL. On this basis, we modified anti-SCCA on the sensor, and other biomarkers of carcinoembryonic-antigen (CEA), neuron-specific-enolase (NSE), CA125, and CA199 were used as comparisons. The results indicated that the sensor modified with HNTs showed a more remarkable frequency shift for the SCCA, which verified that the sensor had good specificity for the SCCA. Therefore, this sensor can be used for highly sensitive and specific detection of the SCCA.

Terahertz (THz) biosensors provide a new avenue for the early diagnosis and treatment of cancers. However, conventional THz biosensors cannot achieve high sensitivity due to limited absorption peaks. In this work, we propose a cancer biomarker ultrasensitive detection method based on THz frequency-comb-like. At first, we design a basic biosensor which has three resonant absorption peaks. Then, we proportionally change the size of basic biosensor and obtain other 4 biosensors with different resonant absorption peaks. Finally, a frequency-comb-like containing 8 uniformly spaced absorption peaks in the range of 0.5 - 1.3 THz is realized by appropriately selecting the absorption peaks of these 5 biosensors. Three cancer biomarkers of carcinoembryonic antigen (CEA), neuron-specific enolase (NSE) and squamous cell carcinoma (SCC) are used as samples of experiment. Under the same concentration, the frequency shifts generated by each peak are accumulated. For samples from 0.1 pg/mL to 50 ng/mL, the cumulative frequency shifts are 122-547 GHz, 168-815 GHz, and 142-505 GHz, respectively. The sensitivity (Sc) of concentration are 64.995 log(ng/ml), 105.005 log(ng/ml), and 62.634 log(ng/ml), respectively. The limit-of-detection (LOD) is 0.1 pg/mL. Compared with other methods using single or few resonant absorption peaks, this method shows higher sensitivity and lower LOD. Therefore, it is valuable for trace molecule detection, biomedical sensing and cancer diagnosis at early stage.

Actively tuning of terahertz (THz) waves through hybrid metasurface has important applications in THz communication, imaging, and modulation. In this paper, we propose a vanadium dioxide (VO ₂ ) hybrid metasurface to realize amplitude modulation of THz orthogonal modes at low triggering voltage. The unit cell of the hybrid metasurface consists of two identical gold crosses and a central bar. And two rectangular VO ₂ patterns are symmetrically embedded in the gaps of the crosses. The performance of the hybrid metasurface is simulated and optimized by using full wave electromagnetic calculation software. The sample is fabricated using a surface micromachining process and characterized by a THz time-domain-spectroscopy (TDS) system. The experimental results show that, the amplitude modulation depth reaches 68% in the range of 0.1∼0.8 THz for transverse-magnetic (TM) mode. Moreover, the hybrid metasurface changes from the transparency to the stopband near 0.43 THz for transverse-electrical (TE) mode. A switching time of 1.9 s is achieved when the triggering current is 520 mA and the voltage is 3.65 V. Most importantly, a fast response area is found. If the metasurface is biased with a current of 430 mA near the fast response area, it's easy to switch quickly. This work paves a new way for the miniaturization and integration of electronic-controlled THz switches and modulators.

Acetone gas can give rise to serious harm to the ecological environment and human health. In addition, acetone gas in the human exhaled breath can be used as an important biomarker for diabetes, lung cancer, lipid peroxidation and other diseases. Therefore, the detection of trace acetone gas is important for environment monitoring and disease diagnosis. Here, a four-split-ring-resonator terahertz (THz) metasurface sensor is proposed to detect trace acetone gas with high sensitivity, and the sample is fabricated using micromachining process. A new Metal-organic-framework (MOF) material Zeolitic-Imidazolate-Framework-90 (ZIF-90) is modified on the surface of the sensor to improve its specificity for acetone gas. When the concentration increases from 10 ppm (parts per million) to 100 ppm, the frequency shift of the sensor shows good linear with the concentration. The minimum measurable concentration is 10 ppm, and sensitivity is 0.1 GHz/ppm (or 10 ppm/GHz). This work paves a way for developing novel biosensors with high sensitivity and specificity, and it has potential applications in the fields of trace gas detection and disease diagnosis at early stage.