Abstract-Determination of pesticides in a flour substrate by chemometric methods using terahertz spectroscopy

Binghua Cao,  Hui Li.   Mengbao Fan,  Wei Wang, Mengyun Wang

https://pubs.rsc.org/en/content/articlelanding/2018/ay/c8ay01728j#!divAbstract

Terahertz time-domain spectroscopy (THz-TDS) is utilized as an effective tool for quantitative analysis of imidacloprid and carbendazim in a flour substrate. The partial least squares (PLS), principal component analysis (PCA), support vector machine (SVM) and PCA-SVM methods were used to construct linear and nonlinear regression models to correlate absorption spectra and concentrations of 21 samples based on the whole absorption spectra (0.2–1.4 THz). The multiple spectra baseline correction (MSBC) method which is based on asymmetric least squares smoothing was adopted to correct the slope baselines. The algorithm can eliminate scatter effects on the spectra and improve the signal-to-noise ratio of the THz spectra. The models were optimized by cross-validation, and their performances were evaluated with respect to root mean square error of prediction (RMSEP), correlation coefficient in the prediction set (Rp) and correlation coefficient in the calibration set (Rc). The results show that PLS delivers the best performance with the lowest errors. The optimized PLS models for both imidacloprid and carbendazim are obtained with RMSEP = 0.5439%, Rp = 0.9992 and Rc = 0.9999. Our experimental results also demonstrate that THz-TDS combined with chemometrics can be used for quantitative determination of pesticides in agricultural products.

Abstract-Spectral Characterization and Molecular Dynamics Simulation of Pesticides Based on Terahertz Time-Domain Spectra Analyses and Density Functional Theory (DFT) Calculations

Fangfang Qu,  Lei Lin, Yong He,  Pengcheng Nie, Chengyong Cai, Tao Dong,  Yi Pan,  Yu Tang,  Shaoming Luo

http://www.mdpi.com/1420-3049/23/7/1607

This work provides the experimental and theoretical fundamentals for detecting the molecular fingerprints of six kinds of pesticides by using terahertz (THz) time-domain spectroscopy (THz-TDS). The spectra of absorption coefficient and refractive index of the pesticides, chlorpyrifos, fipronil, carbofuran, dimethoate, methomyl, and thidiazuron are obtained in frequencies of 0.1–3.5 THz. To accurately describe the THz spectral characteristics of pesticides, the wavelet threshold de-noising (WTD) method with db 5 wavelet fucntion, 5-layer decomposition, and soft-threshold de-noising was used to eliminate the spectral noise. The spectral baseline correction (SBC) method based on asymmetric least squares smoothing was used to remove the baseline drift. Spectral results show that chlorpyrifo had three characteristic absorption peaks at 1.47, 1.93, and 2.73 THz. Fipronil showed three peaks at 0.76, 1.23, and 2.31 THz. Carbofuran showed two peaks at 2.72 and 3.06 THz. Dimethoate showed three peaks at 1.05, 1.89, and 2.92 THz. Methomyl showed five peaks at 1.01, 1.65, 1.91, 2.72, and 3.20 THz. Thidiazuron showed four peaks at 0.99, 1.57, 2.17, and 2.66 THz. The density functional theory (DFT) of B3LYP/6-31G+(d,p) was applied to simulate the molecular dynamics for peak analyzing of the pesticides based on isolated molecules. The theoretical spectra are in good agreement with the experimental spectra processed by WTD + SBC, which implies the validity of WTD + SBC spectral processing methods and the accuracy of DFT spectral peak analysis. These results support that the combination of THz-TDS and DFT is an effective tool for pesticide fingerprint analysis and the molecular dynamics simulations.

Abstract-Ultrasensitive Detection of Residual Pesticides Using THz Near-Field Enhancement

Lee Dong-Kyu, Kim Giyoung Chulki, Min  Jhon Young, Kim Jae Hun,  Lee Taikjin,  Son Joo-Hiuk, Seo Minah,
http://www.ieeeexplore.ws/xpl/articleDetails.jsp?arnumber=7454771&filter%3DAND%28p_IS_Number%3A5741778%29

We present a novel type of highly sensitive and selective detection method for residual pesticide molecules including, e.g., methomyl using nanoscale metamaterials based terahertz (THz) time-domain spectroscopy (TDS) system. Nanoscale slot-antenna-based metamaterials were designed for the strong THz resonance at a certain frequency, where the specific molecule has intramolecular or intermolecular collective vibrational mode. Enhanced THz near-field via a nano-antenna metamaterial strongly increases absorption cross section, and this leads to the detection sensitivity up to parts-per-billion level even in a solution state of pesticide sample. Measured transmittance and reflectance spectrum results show excellent performances in both sensitivity and selectivity. We also imaged reflected THz signals though our THz nano-metamaterials in a nondestructive manner to simply detect the contained residual pesticide at the surface of an apple as it is, without any treatment. This observation can offer the possibility for further various applications as prompt and accurate molecule sensing tools in real time.