WTe₂ Weyl semimetal conical microarray enabled quantum-enhanced terahertz photocurrent sensing for organophosphorus...

As a representative topological quantum system, type-II Weyl semimetals break the fundamental bandgap limitation of conventional semiconductor photodetectors and deliver giant intrinsic nonlinear optical response originating from topologically protected Weyl points and Fermi arc surface states, providing a disruptive material platform for advanced room-temperature terahertz (THz) optoelectronics. Building on this quantum material advantage, we develop a room-temperature THz sensor based on a periodic WTe₂ conical microarray for quantitative detection of the organophosphorus neurotoxin chlorpyrifos in simulated body fluid (SBF). Each microcone measures 80 µm in base diameter and 60 µm in height, arranged with a 100 µm center-to-center pitch on a Si/SiO₂ substrate with Au/Ti electrodes. A 140 GHz continuous-wave THz source illuminates the chip from above, and the photocurrent is read out by a Keithley 2400 digital source meter via two tungsten-carbide microprobes. Leveraging the geometric near-field concentration effect at the cone tips, the proposed architecture synergistically enhances the second-order nonlinear photocurrent rectification originating from the Weyl-point band structure of WTe₂, as confirmed by CST electromagnetic simulation. The underlying sensing mechanism relies on chlorpyrifos-induced dielectric screening and interfacial charge transfer at the WTe₂ surface, which modulate the THz-to-DC rectification efficiency. Current responsivity (Ra) and noise-equivalent power (NEP) are extracted from illuminated and dark current-voltage (I-V) characteristics as a function of chlorpyrifos concentration over a bias range of 7.0-8.0 V. The sensor achieves a limit of detection (LOD) of 12 ng/mL across a dynamic range of 0.05-100 µg/mL in 0.7% saline SBF, with a logarithmic calibration fit of R² = 0.991. Compared with conventional semiconductor and thermal THz detectors, the topological-quantum-material device realizes room-temperature high-sensitivity detection without relying on interband transition or cryogenic cooling, demonstrating fundamentally superior performance stability and broadband adaptability. This work demonstrates that microstructured Weyl semimetal heterostructures enable quantum-enhanced THz biochemical sensing, providing a new device architecture for label-free, reagent-free toxin detection in complex aqueous environments.