WTe ₂ -coated cross-shaped rotatable metasurface terahertz biosensor for high-sensitivity blood iron ion detection at 0.1 THz

This study introduces a terahertz (THz) biosensor for detecting blood Fe³⁺, addressing the limitations of conventional methods such as spectrophotometry, atomic absorption spectrometry, and electrochemical assays, which often suffer from matrix interference, high cost, and electrode fouling. The core innovation of our approach lies in the synergistic integration of a rotatable cross-shaped metasurface with a tungsten ditelluride (WTe₂) coating. This design distinctively enhances sensitivity through polarization-dependent resonant absorption at 0.1 THz, a frequency specifically matched to the ligand-field vibrational modes of Fe³⁺-containing complexes (e.g., transferrin-bound Fe³⁺). The WTe₂ layer, a type-II Weyl semimetal, transduces the enhanced THz absorption into measurable photocurrent changes with high efficiency due to its ultrahigh carrier mobility (>10,000 cm²V^-1s^-1). Experimental results provide concrete evidence of superior performance: a wide linear detection range from 0.1 to 1000 μg/L (with ΔI/I₀ showing excellent linearity against log(concentration), R²=0.994), an ultra-low detection limit of 0.05 μg/L, and minimal interference from common blood components like glucose and Ca²⁺, which exhibit negligible absorption at 0.1 THz. These specific metrics demonstrate a significant advancement over traditional techniques, particularly in sensitivity and compatibility with complex biological matrices. Furthermore, the THz-based method enables non-destructive detection. This work establishes a highly accurate, label-free strategy for quantifying blood Fe³⁺, offering substantial potential for clinical monitoring applications.