Haiyang Gu

Nondestructive detection of fish freshness during its preservation by combining electronic nose and electronic tongue techniques in conjunction with chemometric analysis

A new method was developed to detect fish freshness nondestructively by combining electronic nose (E-nose) and electronic tongue (E-tongue) in conjunction with chemometric methods. An E-nose with nine metal oxide semiconductor gas sensors and a commercial E-tongue were employed in this research. Pseudosciaena crocea stored at 4 °C for different days were used as experimental samples. Total viable counts (TVC) of the fish were detected by the conventional method. E-nose and E-tongue data were analyzed by principal component analysis. Three-layer radial basis function neural network (RBF-NN) models were established for qualitative discrimination of the fish freshness. Performances of RBF-NN models with different numbers of principal components (PCs) as the input were compared. Experimental results revealed that the best RBF-NN model was acquired at seven PCs of E-nose data with an optimal performance of 87.9% and 80.0% in the training set and prediction set respectively. While, the best RBF-NN model of E-tongue data analysis was at five PCs with an optimal performance of 86.3% in the training set and 81.8% in prediction set. Another RBF-NN model was built with the combination of E-nose and E-tongue. The result shows that the discrimination rates improved to 94.0% and 93.9% in the training set and prediction set respectively. A support vector machine regression model was applied to establish a relationship between the combined data from E-nose and E-tongue and from TVC values for quantitative determination. A high correlation was found between the merged data and the parameter of TVC with correlation coefficients more than 0.91. The results proved that, a single system of E-nose and E-tongue was enough to classify samples stored on different days at 4 °C, while a higher discrimination rate was acquired by the combination of the two sensors. The combined system could also be used to quantitatively evaluate the fish freshness. In conclusion, the combined system of E-nose and E-tongue in conjunction with appropriate chemometric analysis methods can conveniently and nondestructively evaluate the freshness of fish stored at 4 °C.

Study on the binding ability of cobalt-porphyrin with small volatile organic compounds based on density functional theory

A colorimetric sensor array is a rapid and high sensitivity sensor for the detection and identification of volatile organic compounds. Theoretical investigations are performed to study the binding ability of the colorimetric sensor array with volatile organic compounds. Cobalt-porphyrin is selected to investigate the binding ability of the colorimetric sensor array with small volatile organic compounds. The binding energy of cobalt-porphyrin with small volatile organic compounds, such as O2, N2, H2S, trimethylamine, propanol, propane, ethyl acetate, butanone and so on, is investigated using density functional theory (DFT) methods at three different spin multiplicities: low-spin (singlet), intermediate-spin (triplet) and high-spin (quintet) states. The relative and absolute binding energies of all the complexes are obtained at the optimized geometries. The triplet state is found to have the lowest energy for the CoP–O2 complex, whereas the singlet state has the lowest energy for the other complexes. The binding energies for the complexes considered are in order starting from the lowest energy state: H2S < propane < O2 < N2 < ethyl acetate < butanone < propanol < trimethylamine. This theoretical result can be used to optimize the sensor to increase the detection ability of the colorimetric sensor array.

The Interaction Study of Colorimetric Sensor Array and Volatile Organic Compounds Using Density Functional Theory

Density functional theory method with B3LYP/LANL2DZ basis set was performed to investigate the influence of different cations on the binding process of volatile organic compounds (VOCs) to metalloporphyrins. The optimized ground state of VOCs-metalloporphyrins is carried out to calculate binding energies, relative spin state energies, electron density, and mulliken charge. The cation has a large effect in the above calculation results. However, all the results can be cross validated by the others. The calculated binding energies can be used as the indicators to design colorimetric sensor array (CSA). While mulliken charge is another way to select the proper sensors to detect VOCs without specifically calculating the binding energies. The results of this theoretical investigation were used to design the proper sensors for CSA.