农产品质量安全是社会广泛关注的重大民生问题。 近年来, 农产品生产过程中农药的广泛使用和滥用会导致农药残留, 对人类健康和环境造成潜在危害。 吡虫啉是一种硝基亚甲基类新烟碱内吸杀虫剂, 因其具有广谱、 高效和低毒的特性已广泛用于农业生产中, 但其过量残留也给人类的健康带来了威胁。 首先对超材料结构的透射谱进行了分析, 对共振频率的形成原因进行了解释; 其次分别在超材料结构和二氧化硅基底上涂覆了500 mg·L-1的吡虫啉溶液并进行了测量, 排除了二氧化硅基底的影响; 接着制备了3个梯度15个浓度的吡虫啉溶液, 分别为: 100~500 mg·L-1（梯度为100 mg·L-1）、 10~50 mg·L-1（梯度为10 mg·L-1）、 1~5 mg·L-1（梯度为1 mg·L-1）; 测量了喷涂在超材料结构上的吡虫啉薄膜的太赫兹时域光谱, 根据太赫兹透射谱峰值频率红移量的不同实现了对不同溶液浓度的鉴别, 建立了峰值频率红移量和吡虫啉浓度的函数关系。 实验结果表明, 借助超材料的调制特性, 太赫兹光谱法可以检测到浓度低至1 mg·L-1的吡虫啉薄膜。 将实验测得的不同浓度吡虫啉溶液的折射率, 代入CST软件进行仿真验证, 结果说明不同浓度的吡虫啉的透射曲线具有不同程度的红移, 且红移量随着浓度的增大而增加。 实验和仿真结果表明, 超材料对太赫兹光谱透射峰值频率的调制可用于低浓度吡虫啉含量的太赫兹时域光谱检测。 此研究为食品基质中农药残留的检测提供了一种新方法。

As a type of nitromethylene nicotine insecticide, midacloprid has been widely used in agricultural production due to its wide-spectrum, high efficiency and low toxicity. However, its excessive residue poses a threat to human health. We first analyze the terahertz transmission spectrum of the metamaterial structure and explains the reason for the formation of the resonance frequency. Secondly, both the metamaterial structure and the silica substratecoated with 500 mg·L-1 imidacloprid solution were measured, respectively, and the influence of the silica substrate was excluded. Next, we prepared imidacloprid solutions with three gradients and 15 concentrations, which were respectively: 100~500, 10～50, 1～5 mg·L-1, and then the terahertz time-domain spectra of these imidacloprid films sprayed on the metamaterial were measured. According to the different peak frequency redshifts of terahertz transmission spectrum, the identification of different solution concentrations was realized, and the functional relationship between the peak frequency redshifts and the concentration of imidacloprid was established. The experimental results show that the detectable concentration of imidacloprid film can be as low as 1 mg·L-1 by THz spectroscopy, along with the increase of imidacloprid concentrations, and peak frequency of the red shift curve increased. Lastly, the refractive index of different concentration imidacloprid solution was substituted into CST software for simulation, and results demonstrated that the transmission curves of different concentration imidacloprid had different redshifts. The above experimental and simulation results show that the peak frequency modulation can be used to detect the low concentration imidacloprid by using THz-TDS with metamaterial. This study provides a new method for the detection of pesticide residues in the food matrix.