The aim of this study was to investigate the feasibility of detecting methomyl, a carbamate insecticide, in food matrices (wheat and rice flours) using terahertz time-domain spectroscopy (THz-TDS). In the frequency range 0.1-3 THz, the characteristic THz absorption peaks of methomyl at room temperature were detected at 1 (33.4 cm −1 ), 1.64 (54.7 cm −1 ), and 1.89 (63.0 cm −1 ) THz. For detailed spectral analysis, the vibrational frequency and intensity of methomyl were calculated using solid-state density functional theory to mimic molecular interactions in the solid state. Qualitatively, the simulated spectrum was in good agreement with the experimental spectrum. Analysis of the individual absorption modes revealed that all of the features in the THz spectrum of methomyl were mainly generated from intermolecular vibrations. The peak appearing at 1 THz (33.4 cm −1 ) was then selected and tested for its suitability as a fingerprint for detecting methomyl in food matrices. Its absorbance was dose-dependently distinguishable from that of wheat and rice flours. The calibration curve of methomyl had a regression coefficient of >0.974 and a detection limit of <3.74 %. Accuracy and precision expressed as recovery and relative standard deviation in interday repeatability were in the ranges 78.0-96.5 and 2.83-4.98 %, respectively. Our results suggest that THz-TDS can be used for the rapid detection of methomyl in foods, but its sensitivity needs to be improved.

We have demonstrated that amine and alkyl groups, applied by a simple spin-coating method, can provide an n-type doping effect on graphene sheets. The organic compounds used in this work are based on amine, phenyl amine, butylphenyl amine, benzoylphenyl amine, and tolylvinylphenyl amine groups. The increases in sheet resistance, decreases in transmittance and work function, and shifts of the G peak to higher wavenumbers and the 2D peak to lower wavenumbers in the Raman spectra indicate that graphene was doped to n-type after the graphene sheets were spin-coated by the amine-based compounds. In particular, graphene doped with butylphenyl amine showed the strongest n-type effect among all of the samples because butylphenyl amine has the strongest binding energy with graphene sheets and disperses in nonpolar solvents, suggesting that the binding energy with graphene sheets and the degree of dispersion in solvents are important factors in the doping process. Molecular calculations based on density functional theory confirmed the n-type properties of graphene doped with amine-based compounds. These results suggest that amine and alkyl groups play a crucial role in the n-type doping of graphene.

To improve the electronic properties of graphene, many doping techniques have been studied. Herein, we investigate the electronic and molecular structure of doped graphene using density functional theory, and we report the effects of amine-based benzene dopants adsorbed on graphene. Density functional theory (DFT) calculations were performed to determine the role of amine-based aromatic compounds in graphene doping. These organic molecules bind to graphene through long-range interactions such asπ-πinteractions and C-H⋯πhydrogen bonding. We compared the electronic structures of pristine graphene and doped graphene to understand the electronic structure of doped graphene at the molecular level. Also, work functions of doped graphene were obtained from electrostatic potential calculations. A decrease in the work function was observed when the amine-based organic compounds were adsorbed onto graphene. Because these systems are based on physisorption, there was no obvious band structure change at pointKat the Fermi level after doping. However, the amine-based organic dopants did change the absolute Fermi energy levels. In this study, we showed that the Fermi levels of the doped graphene were affected by the HOMO energy level of the dopants and by the intermolecular charge transfer between the adsorbed molecules and graphene.

In this paper, with terahertz (THz) time‐domain spectroscopy, we measure the characteristic absorption peaks of melamine and analyze their vibrational modes with the help of solid‐state density functional theory (DFT) calculations. The observed strong absorption peaks at 2, 2.27, and 2.61 THz are well reproduced but show red shifts compared to the theoretical results. Detailed normal mode analyses are carried out, which reveals that those THz peaks are generated from intermolecular vibrations. Temperature‐dependent THz measurements suggest that this red shift mainly comes from the temperature effect. Thus, three peaks are assigned to the calculated intermolecular vibrational motions. This result indicates that THz spectroscopy can be a useful tool to detect the details of intermolecular structures.