Tracking the microalgal oil production via SCRS. (A) Averaged SCRS of the 60 cells of Group N- at each time point as well as the Raman spectrum of triolein, a typical TAG species. (B) Averaged SCRS of the 60 cells of Group N + at each time point. (C) PCA scores plot derived from the fingerprint region. (D) PCA scores plot derived from the hydrocarbon region. Each symbol represents the average of twenty cells of a triplicate; the error bars represents SD of the twenty cells. Green diamond: cells at 0 h. Red triangle: cells of Group N+. Blue square: cells of Group N-. h: hours; PCA: principal component analysis; PC: principal component; SCRS: single-cell Raman spectra; SD: standard derivation; TAG, triacylglycerol.