Research On Aflatoxin Detection Based On Terahertz Metamaterials Sensor

Terahertz spectroscopy has been widely used in the fields of medicine detection,food quality detection and drug detection because of its fast response time,simple detection process and high spectral resolution.However,the interaction between the free-space propagating terahertz waves and the sample is weak,resulting in a weak signal,low detection limit and inability to meet the demand for fast and accurate detection of trace samples.Metamaterials is a composite material or structure consisting of a periodically arranged array structure of subwavelength units with specific electromagnetic properties that natural materials do not possess.Terahertz sensors based on metamaterial technology are extremely sensitive to changes in the dielectric constant of the surrounding environment due to their ability to enhance the local electromagnetic field strength and achieve markerless detection,breaking the resolution limit of existing sensors and providing a new detection idea for highly sensitive detection of micro or traces samples.Therefore,this paper focuses on sensor structure design and optimization,physical mechanism analysis,performance analysis,etc.Combining metamaterials,physical optics related theories and spectral signal post-processing methods,we are devoted to the study of terahertz band high performance sensors and their applications in aflatoxin detection.The main research contents are as follows:（1）A highly sensitive dual-frequency terahertz metamaterial absorption type sensor is designed for the current sensor with single-frequency response,low performance and complex structure.The sensor consists of two concentric open-ring resonators with two independently tunable operating frequencies in the range of 0.7-2.5 THz and the absorption rate in free space exceeds 99.9%,which achieves a near-perfect absorption function.In addition,the proposed structure reaches the refractive index sensitivity of 693.7 GHz/RIU and the thickness sensitivity of 107.3 GHz/um,moreover,it shows a high stability at 0°-30°oblique incidence angle and within 4%fabrication error,which can significantly enhance the terahertz wave-matter interactions.（2）In order to study the terahertz radiation response of substances in solution environment and enhance the molecular fingerprint characteristics of trace substances,a terahertz metamaterial sensor is designed in combination with microfluidic technology.We analyze the mechanism of action and performance of the sensor using the finite element method,and the study shows that there are three narrow-band absorption resonances of the sensor,which achieve a perfect match with the free space.In addition,the sensor offers wide polarization angle and incidence angle insensitivity,allowing samples to be tested at the n L level with reduced polar solution-induced absorption,which provides sensitivity to refractive index of859 GHz/RIU.This study will reduce the sample pre-treatment time and provide a solution to achieve ultra-sensitive analysis of substances and rapid detection in the field.（3）A method of aflatoxin detection by spectroscopy based on terahertz metamaterial sensors is proposed to address the problems of large sample usage and low sensitivity of current aflatoxin detection methods.The sensor is fabricated by photolithography,and the absorption characteristic spectrum of the sample is obtained for analysis by using a terahertz time-domain spectral acquisition system.The experimental results showed that the interaction between the sensor and the surface material caused different degrees of resonance frequency shift.According to the amount of frequency shift,the identification of 100 ppm AFB₁,AFB₂,AFG₁ and AFG₂ was achieved,moreover,the concentration-frequency shift model of AFB₁samples was established to achieve ng-level substance detection,and the feasibility of the sensor was verified.