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.

中文翻译：

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使用石墨烯/石墨氮化碳异质结的混合超表面用于具有可调能带结构的超灵敏太赫兹生物传感器

集成新型材料对于太赫兹 (THz) 范围内生物分子的超灵敏、多维检测至关重要。很少有关于太赫兹生物传感器的研究使用具有可调能带结构的半导体活性层。在这项研究中，我们展示了三种基于超表面与石墨氮化碳、石墨烯和异质结的杂交来检测酪蛋白分子的太赫兹生物传感器。我们通过观察三度变化（频移、透射差和相位差）实现了酪蛋白分子的低浓度检测，限度为3.54 ng/mL，并实现了多维传感。酪蛋白对半导体活性层导电性的有利影响可以用来解释内部传感机制。随着带正电荷的酪蛋白浓度的增加，蛋白质分子的掺入通过静电掺杂效应改变了半导体活性层表面的载流子浓度，从而改变了活性层的能带结构和电导率。测量结果表明，通过观察共振频率、传输值和相位差的变化，可以直接区分任何酪蛋白浓度。对于异质结，生物传感器在三种生物传感器中显示出对蛋白质的最高响应。Silvaco Atlas 包用于模拟三个样品的能带结构和载流子传输，以证明异质结对传感器的好处。仿真结果验证了我们提出的理论机制模型。