Broadband spectra of 20 L-amino acids were obtained at room temperature by terahertz time-domain and infrared spectroscopy. The intensity of terahertz absorption peaks varied with the concentrations of amino acids, and the optimum proportion for each amino acid was obtained. An absorption spectral database of 20 L-amino acids was established from 0 to 6 THz. The associations between terahertz absorption peaks and molecular structures of amino acids were analyzed. The terahertz spectra for L-alanine were compared with the calculated results based on density functional theory using two basis sets that were reliably consistent.

As an ingredient of great economic value, Tricholoma matsutake has received widespread attention. However, heavy metal residues and preservatives in it will affect the quality of Tricholoma matsutake and endanger the health of consumers. Here, we present a method for the simultaneous detection of low concentrations of potassium sorbate and lead in Tricholoma matsutakes based on surface-enhanced Raman spectroscopy (SERS) and fluorescence (FLU) spectroscopy to test the safety of consumption. Data fusion strategies combined with multiple machine learning methods, including partial least-squares regression (PLSR), deep forest (DF) and convolutional neural networks (CNN) are used for model training. The results show that combined with reasonable band selection, the CNN prediction model based on decision-level fusion achieves the best performance, the correlation coefficients (R²) were increased to 0.9963 and 0.9934, and the root mean square errors (RMSE) were reduced to 0.0712 g·kg⁻¹ and 0.0795 mg·kg⁻¹, respectively. The method proposed in this paper accurately predicts preservatives and heavy metals remaining in Tricholoma matsutake and provides a reference for other food safety testing.

In this work, we experimentally demonstrate an electrically tunable superconducting composite structure metamaterial capable of modulating terahertz (THz) waves. Compared with other superconducting switching devices, our device is composed of golden structures and niobium nitride (NbN) film junctions together. Its unique structural characteristics allow our device to achieve relatively large amplitude modulation effects with the smallest superconducting films. With a 4 V bias voltage, a modulation depth of 73.8% for this switch can be achieved at 0.308 THz. The experimental results agree well with the simulations. To better illustrate the physical mechanism behind the resonance mode transition, a hybrid coupling model was introduced. Our work provides an alternative tuning method and delivers a promising approach for designing active and miniaturized devices in THz cryogenic systems.

As an important ecosystem on the earth, forests not only provide habitat and food for organisms but also play an important role in regulating environmental elements such as water, atmosphere, and soil. The quality of forest waters directly affects the health and stability of aquatic ecosystems. Chemical oxygen demand (COD) is commonly used to assess the concentration of organic matter and the pollution status of water bodies, which is helpful in assessing the impact of human activities on forest ecosystems. To effectively measure the COD value, water samples were prepared from Purple Mountain in Nanjing and nearby rivers and lakes. Using ultraviolet–visible (UV–vis) and fluorescence (FLU) spectroscopy combined with data fusion, the COD values of the forest water were accurately measured. Due to the large dimensionality of spectral data, the successive projections algorithm (SPA) and competitive adaptive reweighted sampling (CARS) were applied to the selection of characteristic wavelengths. By establishing a discriminant model for single-level data and using the voting mechanism to fuse the output results of different models, a relatively high determination coefficient ($R^2$) of 0.9932 and a low root-mean-square error (RMSE) of 0.4582 were obtained based on the decision-level data fusion model. Compared with the single-spectrum and feature-level fusion models, the decision-level fusion scheme achieves an efficient, comprehensive, and accurate quantification of the water COD value. This study has important applications in forest protection, water resources management, sewage treatment, and the food processing field.

The terahertz spectra of solid-state amino acids with different polarities were measured by terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy. The measured absorption spectra were in good agreement with the results simulated by density functional theory using hybrid functional Becke–3–Lee–Yang–Parr and generalized-gradient approximation Perdew–Burke–Ernzerhof functional with the same basis set of 6-311 G (d, p), respectively. In order to construct a precise crystal structure, dispersion-corrected density functionals were included in the simulation. It was found that Becke–3–Lee–Yang–Parr functional combined with dispersion-correction could produce accurate simulation results that corresponded to the experimental terahertz spectra of solid-state amino acids. However, it greatly increased the time for calculation. The method of Perdew–Burke–Ernzerhof functional with dispersion-correction provided comparable accuracy to Becke–3–Lee–Yang–Parr with dispersion-correction, and much higher simulation speed. The spectral features are assigned as primarily external lattice translations and rotations with lesser contributions to intramolecular torsions.