Fig. 2

Raman spectra of fatty acid standards and microalgal lipids a green excitation (532 nm laser) and b NIR excitation (785 nm laser). Raman spectra are listed with decreasing degree of unsaturation of fatty acid standards from top to bottom and show a gradual decrease in the intensity of Raman band at 1650 rel cm⁻¹ (C=C stretching mode) compared to that of 1440 rel cm⁻¹ band (CH₂ bending mode). Raman peaks in the 2800–3000 rel cm⁻¹ (CH₂ symmetric and asymmetric stretches) are scaled in intensity to allow visualization. These modes are more intense than the peaks at 1440 and 1650 rel cm⁻¹ when using the green excitation and much weaker than the peaks at 1440 and 1650 rel cm⁻¹ when using the NIR excitation