Traditional Chinese Medicine （TCM） plays a crucial role in global healthcare； however， the growing popularity of herbal medicinal products has raised significant concerns regarding potentially hazardous pesticide residues.

Ligusticum chuanxiong

， a widely used TCM prized for its analgesic， anti-tumor， and anti-inflammatory properties， is highly susceptible to fungal infections such as

Sclerotinia sclerotiorum

and

Botrytis cinerea

during its artificial cultivation. To combat these diseases， procymidone， a cost-effective and highly efficient organochlorine fungicide， is frequently applied. Due to its high chemical stability and prolonged environmental half-life， persistent procymidone residues can easily accumulate within ecosystems and herbal matrices. Toxicological research demonstrates that excessive dietary exposure to procymidone can inhibit androgenic activity， disrupt endocrine functions， and induce adverse effects on the reproductive， digestive， and nervous systems. Consequently， stringent Maximum Residue Limits （MRLs） have been established globally， with the European Union mandating an MRL of 0.02 mg/kg for herbal products. Conventional pesticide residue detec

tion methods， including Gas Chromatography-tandem Mass Spectrometry （GC-MS） and High-performance Liquid Chromatography （HPLC）， offer high sensitivity but are fundamentally limited by prolonged detection times， complex sample pretreatment procedures， and the need for specialized personnel. Conversely， standard spectroscopic analysis methods can reduce operational time but generally possess lower detection sensitivity， rendering them inadequate for trace-level residue analysis. Therefore， the objective of this study is to develop a rapid and highly sensitive detection method utilizing a terahertz （THz） metamaterial sensor to quantify trace procymidone residues in complex TCM matrices.To address the critical limitations of conventional analytical techniques， this study proposes a novel sensing platform combining THz time-domain spectroscopy with a specifically designed metamaterial sensor. THz waves exhibit high penetration， low photon energy， and distinct spectral features， making them highly suitable for non-destructive and label-free chemical detection. The fabricated THz metamaterial sensor features an artificially engineered asymmetric square ring chain resonator composed of periodically arranged subwavelength structures. This specific structural design introduces asymmetric microperturbations that significantly enhance the localized electromagnetic field and improve the quality factor of the dipole resonance compared to symmetric designs. When pesticide molecules adhere to the sensor surface， small local electric field perturbations are generated in the surrounding dielectric environment， which ultimately manifest as highly sensitive changes in the THz resonance peak frequency. In the experimental procedure， procymidone standard solutions were systematically prepared across a trace concentration gradient ranging from 1 to 82 μg/L. Subsequently， organically cultivated and commercial

Ligusticum chuanxiong

samples were ground into powder and subjected to an extraction process using dimethyl sulfo

xide as the solvent due to its optimal solubility. Small volumes of the resulting supernatants were accurately pipetted onto the surface of the THz metamaterial sensor and dried in a controlled environment. The THz absorbance spectra were then continuously recorded， and the resonance peak frequency shifts were extracted to establish quantitative regression models linking the frequency shift to the exact pesticide concentration.Experimental evaluations of the proposed THz metamaterial sensor revealed exceptional localized electromagnetic field enhancement and superior sensing capabilities. Upon the application of the pure procymidone standard solutions， the THz-TDS system captured stable and highly distinguishable frequency shifts， demonstrating that as the pesticide concentration increased， the resonance peaks of the metamaterial exhibited a clear red-shift toward lower frequencies. A quantitative concentration-frequency shift model was successfully established utilizing the Michaelis-Menten equation， yielding a remarkably high fitting coefficient （

R

2

0.98）. Most notably， the asymmetric metamaterial sensor achieved an ultra-low limit of detection of 0.52 μg/L for procymidone， significantly outperforming previously reported THz biosensors. During the practical validation phase involving the complex TCM matrix， the sensor successfully maintained its high detection sensitivity. The regression curves constructed for procymidone within the

Ligusticum chuanxiong

DMSO extracts similarly demonstrated a strong nonlinear fitting correlation， proving that the unique subwavelength structure effectively amplifies the dielectric perturbation caused by the target molecules while overcoming residual background interferences from the herbal matrix. Furthermore， the entire sample preparation and detection workflow could be seamlessly completed within 30 minutes， drastically reducing the operational timeframe compared to traditional chromatographic analyses.In summary， this study experi

mentally demonstrates the feasibility and substantial advantages of utilizing a highly sensitive THz metamaterial sensor for the quantitative detection of trace procymidone residues in the TCM

Ligusticum chuanxiong

. By rationally designing an asymmetric square ring chain structure， the localized electromagnetic interactions between the THz waves and the pesticide molecules are significantly amplified， enabling an unprecedented μg/L-scale detection limit. This detection threshold strictly complies with the stringent MRLs established by international regulatory bodies. This approach successfully circumvents the time-consuming and expensive drawbacks of conventional GC-MS methods while entirely resolving the sensitivity bottlenecks of standard optical spectroscopy. Ultimately， combining the physical characteristics of the THz metamaterial sensor with reliable mathematical modeling provides a label-free， rapid， and highly effective technological strategy. This study offers a promising new testing solution for the rigorous safety monitoring and quality control of TCM materials， contributing significantly to the prevention of potential pesticide-related health risks.