Terahertz Sensor for Trace Pb²⁺ in Liquid Based on Weyl Semimetal Films with External Field Modulation

The rapid, nondirect contact and ultrasensitive detection of trace lead ions (Pb²⁺) in liquid environments remains a critical challenge for environmental monitoring and public health protection. Conventional analytical techniques often require complex sample pretreatment, direct electrode contact, or bulky instrumentation, limiting their practical applicability. Here, we report a nondirect contact, label-free terahertz (THz) sensor operating at 0.1 THz, based on Weyl semimetal (WSM) thin films fabricated by magnetron sputtering and integrated with an interdigitated electrode structure. The sensing response arises from the modulation of terahertz conductivity in Weyl semimetals triggered by adsorbed Pb²⁺, supported by the material's topological surface states, high carrier mobility, and nonlinear transport properties associated with Berry curvature. Laser illumination and acoustic excitation are introduced as auxiliary modulation strategies to enhance the signal-to-noise ratio, increase response amplitude, and reduce the noise-equivalent power (NEP), thereby further improving the detection sensitivity. The sensor reaches a limit of detection of 6.0 ng/L for Pb²⁺ in liquid samples and exhibits a linear concentration response relationship. This work integrates topological quantum materials, terahertz optoelectronics and synergistic multiphysics field regulation to establish a feasible sensing framework, offering a practical route toward real-time field environmental monitoring and liquid trace heavy metal quantification.