Biosensors are a focus of research on terahertz metasurfaces. However, reports of ultra-sensitive biosensors based on Dirac points are rare. Here, a new terahertz metasurface is proposed that consists of patterned graphene and perovskites. This serves as an ultra-sensitive Dirac-point-based biosensor for qualitative detection of sericin. Theoretically, sericin may make graphene n-doped and drive the Fermi level to shift from the valence band to the Dirac point, causing a dramatic decrease in conductivity. Correspondingly, the dielectric environment on the metasurface undergoes significant change, which is suited for ultra-sensitive biosensing. In addition, metal halide perovskites, which are up-to-date optoelectronic materials, have a positive effect on the phase during terahertz wave transmission. Thus, this sensor was used to successfully detect sericin with a detection limit of 780 pg/mL, achieved by changing the amplitude and phase. The detection limit of this sensor is as much as one order of magnitude lower than that of sensors in published works. These results show that the Dirac-point-based biosensor is a promising platform for a wide range of ultra-sensitive and qualitative detection in biosensing and biological sciences.

A depletion layer played by aqueous organic liquids flowing in a platform of microfluidic integrated metamaterials is experimentally used to actively modulate terahertz (THz) waves. The polar configuration of water molecules in a depletion layer gives rise to a damping of THz waves. The parallel coupling of the damping effect induced by a depletion layer with the resonant response by metamaterials leads to an excellent modulation depth approaching 90% in intensity and a great difference over 210° in phase shift. Also, a tunability of slow-light effect is displayed. Joint time-frequency analysis performed by the continuous wavelet transforms reveals the consumed energy with varying water content, indicating a smaller moment of inertia related to a shortened relaxation time of the depletion layer. This work, as part of THz aqueous photonics, diametrically highlights the availability of water in THz devices, paving an alternative way of studying THz wave–liquid interactions and developing active THz photonics.