Terahertz Spectrum Detection And Identification Of Aflatoxins B1 And B2

Aflatoxins are a class of highly toxic compounds that have been classified as class I carcinogens by the World Health Organization(WHO)Cancer Research Institute.The acute toxicity of aflatoxin B1 is 68 times that of arsenic,and the carcinogenic ability is 75 times that of Dimethylnitrosamine.The chemical structure of aflatoxin B2 and aflatoxin B1 is similar,and the toxicity and carcinogenicity are relatively weak.At present,the main methods for the detection of aflatoxins are thin film chromatography and liquid chromatography.However,problems such as long detection period,complicated operation,and various reagents are common,which is difficult to meet the requirements of modern detection.Therefore,it is urgent to apply a quick,simple,specific sensitive and low-cost detection method for aflatoxins.As a new type of non-destructive testing technology,terahertz time-domain spectroscopy technology has the advantages of low photon energy,wide spectral range and rich spectral information.It can be used for qualitative or quantitative non-destructive analysis of substances.It has potential application value in food and agricultural product safety testing.In this paper,two kinds of aflatoxin(AFT),Aflatoxin B1(AFB1)and aflatoxin B2(AFB2),which are common in grain and oil feed,are tested and assisted by Raman spectroscopy.By means of terahertz time-domain spectroscopy as the main line of research,a method for the detection and identification of aflatoxins B1 and B2 and a qualitative and quantitative analysis model were established.The Raman scattering spectra of AFB1 and AFB2 pure powders,the surface-enhanced Raman spectra of solution samples and the terahertz spectral characteristics of AFB1 and AFB2 tablet were obtained experimentally.In order to further improve the sensitivity of the detection,we developed a sensing technology based on terahertz metamaterial chip,which enhanced the difference of THz band between the two samples by surface plasmon resonance,and realized the high sensitivity,no mark and low of AFB1 and AFB2.The rapid detection of the dose provides a new idea for the determination of aflatoxin in grain and oil feed.The main research contents of this thesis are as follows:(1)Raman scattering spectra of AFB1 and AFB2 powders in 500-2000 cm-1 band and Nano-Silver substrate surface enhanced Raman spectroscopy in 500-1600 cm-1 band AFB1 and AFB2 solutions by Raman spectroscopy system,Using Gaussian09 quantum chemistry program the medium-density functional theory was used to calculate the molecular dynamics of individual molecules of AFB1 and AFB2,and the theoretically calculated Raman scattering spectra of AFB1 and AFB2 were obtained.It was found that the Raman scattering spectra of AFB1 and AFB2 powders could not be detected and identified.The Raman enhancement spectra of AFB1 and AFB2 solutions have Raman fingerprint characteristics of aflatoxin.The overall waveform and peak position of the two samples are relatively high.Consistent,but there are Raman spectral features that can identify the two samples,so Raman spectroscopy can be used to detect AFT and can effectively identify AFB1 and AFB2;the vibrational spectra calculated by density functional theory can effectively explain the experimental results and clarify the sources of Raman characteristic peaks of AFB1 and AFB2.(2)After mixing the AFB1,AFB2 sample powder and polyethylene powder in a proportional manner,the sample is prepared by tableting,transmission experiments were carried out on the tablets using the terahertz time-domain spectroscopy system,and the time-domain spectra of the two samples were measured in the 0-3.0 THz band.The absorption coefficient and refractive index of the sample were extracted by the theory of plate medium.The absorption coefficient,extinction coefficient,refractive index and dielectric constant of AFB1 and AFB2 pure products in the mixed pellets were extracted by the effective medium theory.The samples were detected and identified by analyzing the absorption and refractive index spectra of the sample mixed pellets in the 0.5-2.5 THz band and the absorption coefficient,extinction coefficient,refractive index and dielectric constant ?r spectrum of the pure product.(3)Based on the qualitative identification of AFB1 and AFB2 by terahertz spectroscopy,the asymmetric double-crack ring structure on the ultra-thin flexible substrate is selected as the metamaterial sensor.The characteristic transmission spectra of AFB1 and AFB2 solutions in the 0.7-1.1 THz band were tested and analyzed;according to the relative transmission intensity at the resonant frequency of the empty metamaterial and the central resonance frequency shift,not only the AFB1 and AFB2 aflatoxins can be qualitatively identified,but also the content can be quantitatively identified.In order to verify the experimental results,the CST software finite element module was used to simulate the LC intrinsic resonance mode and its sensing effect of the asymmetric double-opening split-cavity metamaterial sensor.The simulation results were consistent with the experimental results,and the terahertz metamaterial sensor used was verified.Detect and identify the validity of AFB1 and AFB2 and the accuracy of experimental test results.