Lipids monitoring in Scenedesmus obliquus based on Terahertz Technology

Abstract Background Microalgae are considered as a source of low pollution and renewable fuel due to their ability to synthesize an abundance of lipids. Conventional methods for lipid quantification are time consuming and chemically contaminated. Spectroscopic method combined with mathematical model can be used for qualitative and quantitative analysis of material composition.Terahertz technology provides not only timely and nondestructive testing without chemical pollution, but also information about the functional group vibration mode and structure of the measured components. Therefore,terahertz is proposed for microalgae metabolism detection. Results The aim of this study was to use Terahertz (THz) spectroscopy to observe lipid content in Scenedesmus obliquus (S. obliquus). We collected the THz spectra of S. obliquus which were cultivated under nitrogen stress and THz spectroscopy was used to analyze changes in substance components (lipids, proteins, carbohydrates and β-carotene). Partial least square was used to establish the prediction model of each stress time point. The correlation coefficient of the prediction results of the model was above 0.991, and the root mean square error was less than 0.020. It indicated that THz technology can be used to discriminate S. obliquus cells under different nitrogen stress culture times effectively. The correlation between the THz characteristic peak (9.3 THz) and the total lipid content determined by gravimetry reaches 0.96. The final results were compared with the commonly used spectroscopic methods for lipid observation (Raman spectroscopy). Conclusions The prediction accuracy of model of THz bands is relatively high. It indicated that THz technology can be used to monitor the change of material composition in microalgae under nitrogen stress. THz is more accurate than Raman in total lipid monitoring. For the research of microalgal metabolites, compared with Raman technology, there is more research space for THz technology. THz technology can provide technical supporting for the engineering culture of oil-producing microalgae under environmental control in future.