Most DNA methylation occurs in the cytosine of nucleosides. In this study, the absorption coefficients of cytosine and 5-methylcytosine were measured at 0.1-2.0 THz through terahertz time domain spectroscopy (THz-TDS) without being labeled. Our results showed that these important biomolecules had distinct spectral characteristics within this terahertz band. Moreover, structural optimization and lattice dynamics calculations were performed to determine the lattice vibrational motions of both cytosine crystals and 5-methylcytosine crystals using the density functional theory (DFT) and the properly modeled intermolecular potentials. Typically, the lattice vibrational motion simulated the absorption spectrum which indicated that the terahertz technique was able to detect the absorption spectral features of cytosine and 5-methylcytosine. Hopefully, this study provided the molecular background to detect DNA methylation and lay certain foundation for subsequent cancer detection.
The terahertz time-domain spectra of sildenafil, metformin hydrochloride and phenolphthalein samples were obtained by terahertz time-domain spectroscopy. The refractive index spectra and absorption spectra of these additives were obtained according to the formula. The experimental results show that these three health supplements have obvious characteristic absorption peaks in the terahertz band. The illegal additives were classified based on support vector machine (SVM). The experimental results show that the established SVM model can accurately identify the check set and identify the additive within a certain range. The feasibility of terahertz time-domain spectroscopy for food ingredient detection was verified, which provided a new experimental method for the detection of health product additives.
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