QBIC-Terahertz Metasurface for Quantitative Detection of Chlorpyrifos in Soybean Oil in a Liquid State

Resonances originating from the concept of bound states in the continuum (BIC) have been shown to produce high quality factors and strong field enhancements. Here, an ultrasensitive terahertz (THz) metallic metasurface based on BIC is developed to address the limited sensitivity of THz sensing technology. The metasurface employs a u-shaped resonator and an l-shaped resonator as the unit cell, and a resonance around 0.7 THz can be excited. The analysis of the quality factor and the band structure confirms that this resonance is induced by the BIC mode. Based on the calculations, it can be concluded that the frequency shift changes linearly as a function of analyte thickness within the range of 0–10 μm, and the sensitivity can be as high as 151 GHz/RIU. The feasibility of the detection of chlorpyrifos concentration in soybean oil is assessed experimentally, and a liquid cell is applied as a sample holder to maintain the sample in a liquid state. It can be concluded that the metasurface enables effective detection of chlorpyrifos in soybean oil, with a limit of detection (LOD) as low as 0.007 mg/L. Our work enables the detection of trace chlorpyrifos in soybean oil, facilitating the application of THz technology in food safety.