title: Rapid in vivo lipid/carbohydrate quantification of single microalgal cell by Raman spectral imaging to reveal salinity-induced starch-to-lipid shift.
abstract: BACKGROUND
  Lipid/carbohydrate content and ratio are extremely important when engineering algal cells for liquid biofuel production. However, conventional methods for such determination and quantification are not only destructive and tedious, but also energy consuming and environment unfriendly. In this study, we first demonstrate that Raman spectroscopy is a clean, fast, and accurate method to simultaneously quantify the lipid/carbohydrate content and ratio in living microalgal cells.
  
  
  RESULTS
  The quantification results of both lipids and carbohydrates obtained by Raman spectroscopy showed a linear correspondence with that obtained by conventional methods, indicating Raman can provide a similar accuracy to conventional methods, with a significantly shorter detection time. Furthermore, the subcellular resolution of Raman spectroscopy enabled not only the concentration mapping of lipid/carbohydrate content in single living cells, but also the evaluation of standard deviation between the biomass accumulation levels of individual algal cells.
  
  
  CONCLUSIONS
  In this study, we first demonstrate that Raman spectroscopy can be used for starch quantification in addition to lipid quantification in algal cells. Due to the easiness and non-destructive nature of Raman spectroscopy, it makes a perfect tool for the further study of starch-lipid shift mechanism.
authors.affiliation: Department of Chemistry, the University of Tokyo, Tokyo, 113-0033 Japan.
authors.forename: Liang-da
authors.identifier: 0000-0002-8178-1800
authors.initials: LD
authors.lastname: Chiu
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin, 150090 People's Republic of China.
authors.forename: Shih-Hsin
authors.initials: SH
authors.lastname: Ho
authors.affiliation: Department of Chemistry, the University of Tokyo, Tokyo, 113-0033 Japan.
authors.forename: Rintaro
authors.initials: R
authors.lastname: Shimada
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin, 150090 People's Republic of China.
authors.forename: Nan-Qi
authors.initials: NQ
authors.lastname: Ren
authors.affiliation: Department of Chemistry, the University of Tokyo, Tokyo, 113-0033 Japan.
authors.forename: Takeaki
authors.initials: T
authors.lastname: Ozawa
keywords: Raman spectroscopy; Single-cell analysis; Starch–lipid shift