Agro-product Safety Detection By Integrating Terahertz Spectroscopy,Metamaterials And Nanomaterials:Mechanisms And Methods

Terahertz(THz)technology is speedy and user-friendly which can provide molecular vibration information of samples,holding great potential of development and application in biological detection field.However,the weak interaction between free THz wave and sample can not meet the requirements of detecting sample on trace amount level.As an electric field enhancement device,metamaterials have been widely used for the detection of trace amount sample and have gradually become a new type of sensor device.In this thesis,with the assistance of metamaterials,THz time-domain spectroscopy is utilized along with nanomaterials(gold nanoparticles and graphene)for the study of strong interaction between THz electric field and materials.The quantitative detection model based on THz metamaterials and nanotechnology is established and used for the detection of pesticide and protein.For the first time,we integrate THz spectroscopy,metamaterials and nanomaterials(gold nanoparticles and graphene)respectively for simple and fast detection of protein and pesticide,providing new methods for pesticide residue detection in agro-products and biosensing technology.The main research contents and results of this work are as follows.(1)Chlorpyrifos-methyl was selected as the sensing target.THz absorption spectra of chlorpyrifos-methyl was studied by pressing the sample into pellets.A metamaterial absorber was utilized as a signal enhancing tool for chlorpyrifos-methyl detection,reaching a limit of detection to 0.204 mg L-1.(2)To investigate the relationship between the sensitivity of the metamaterial absorber and the optical parameters of sample,fructose and L-histidine were selected as sensing targets and theoretical simulations and experimental tests were conducted.Avidin and gold nanoparticles were integrated through electrostatic adsorption.The introduction of gold nanoparticles can significantly increase the sensitivity of metamaterials,which is able to detect fmol level of sensing targets.(3)A graphene-metamaterial absorber heterostructure was constructed and characterized for molecule detection.Theoretical simulations and experimental tests were used to interpret the increase of Q-factor and the blue shift of the resonant peak during detection process.This device could be used in chlorpyrifos-methyl detection,which is able to detect 0.02 mg L-1 of chlorpyrifos-methyl solution.With the decoration of aptamers,this device could serve as a biosensor,which specifically captured thrombin molecules(the concentration of thrombin solution is 100 nM).(4)The graphene-metamaterial absorber heterostructure was used for detecting lixiviums of unhusked rice and husked rice which were mixed with chlorpyrifos-methyl.The results showed the feasibility of detecting chlorpyrifos-methyl in lixivium of unhusked rice by using this heterostructure,which is hopeful to achieve the requirements of national food safety standards.