提出一种石墨烯-金属超材料复合太赫兹传感器，充分利用石墨烯能带Dirac点附近费米能级对样品的灵敏响应结合超材料表面强局域电场实现了对谷氨酸溶液浓度的多维超灵敏传感。实验结果表明，传感器在频率f =0.58 THz处存在一个明显的透射峰，且该透射峰幅值随谷氨酸溶液浓度的增加先升高后降低。若以透射峰幅值作为传感指标，器件能够探测到的最低浓度在10⁻¹ fg/mL量级。另外，从传感器的透射波相位差-频率关系曲线中提取的斜率与浓度具有类线性关联，这意味着相位差信息也可以作为有效的传感指标。结合透射幅值和相位差两个传感指标，器件可以实现对谷氨酸溶液浓度的超灵敏精确检测。文中提出的器件为发展基于太赫兹超材料的超灵敏氨基酸传感器提供了帮助。

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.

Reference frame independent and measurement device independent quantum key distribution (RFI-MDI-QKD) has the advantages of being immune to detector side loopholes and misalignment of the reference frame. However, several former related research works are based on the unrealistic assumption of perfect source preparation. In this paper, we merge a loss-tolerant method into RFI-MDI-QKD to consider source flaws into key rate estimation and compare it with quantum coin method. Based on a reliable experimental scheme, the joint influence of both source flaws and reference frame misalignment is discussed with consideration of the finite-key effect. The results show that the loss-tolerant RFI-MDI-QKD protocol can reach longer key rate performance while considering the existence of source flaws in a real-world implementation.