Micro‐Raman spectroscopy of algae: Composition analysis and fluorescence background behavior

Abstract

Preliminary feasibility studies were performed using Stokes Raman scattering for compositional analysis of algae. Two algal species, Chlorella sorokiniana (UTEX #1230) and Neochloris oleoabundans (UTEX #1185), were chosen for this study. Both species were considered to be candidates for biofuel production. Raman signals due to storage lipids (specifically triglycerides) were clearly identified in the nitrogen-starved C. sorokiniana and N. oleoabundans, but not in their healthy counterparts. On the other hand, signals resulting from the carotenoids were found to be present in all of the samples. Composition mapping was conducted in which Raman spectra were acquired from a dense sequence of locations over a small region of interest. The spectra obtained for the mapping images were filtered for the wavelengths of characteristic peaks that correspond to components of interest (i.e., triglyceride or carotenoid). The locations of the components of interest could be identified by the high intensity areas in the composition maps. Finally, the time evolution of fluorescence background was observed while acquiring Raman signals from the algae. The time dependence of fluorescence background is characterized by a general power law decay interrupted by sudden high intensity fluorescence events. The decreasing trend is likely a result of photo-bleaching of cell pigments due to prolonged intense laser exposure, while the sudden high intensity fluorescence events are not understood.

Raman Spectroscopy of Microbial Pigments

“…Confocal Raman spectroscopy was used to differentiate and map the relation between a carotene-containing yeast and Pseudomonas aeruginosa cells in living, hydrated, composite biofilms on the basis of their spectral signatures (97). The presence of carotenoids, chlorophyll, and triglycerides was monitored in healthy and starved colonies of the algae Chlorella sorokiniana and Neochloris oleoabundans (98). The distribution of carotenoids in different microalgae (Dunaliella, Phaeodactylum, Haematococcus pluvialis, Thermosynechococcus elongatus) was mapped at the cellular level (99-103) using slightly different instrumental settings (Fig.…”

In vivo lipidomics using single-cell Raman spectroscopy

“…Specifically, laser-trapping Raman spectroscopy (LTRS), a combination of a near-IR optical trap and a micro-Raman system (22)(23)(24)(25), is particularly well suited to meet these requirements. LTRS affords in vivo spectroscopy from single living cells, producing spectra with significantly higher signal-to-noise ratios, without any preparation step (Movies S1 and S2), than conventional Raman measurements performed on bulky, dried, or immobilized algal samples (26)(27)(28) and thus enables a different level of quantitative analysis. As demonstrated in this work, a Raman spectral library of model microalgal lipids can be conveniently generated and applied readily to obtain quantitative information such as the degree of unsaturation (quantified by the average number of C═C bonds per lipid molecule), lipid chain length, and melting tem-perature (T m ) of the constituent fatty acids in microalgae by using single-cell measurements.…”

Raman Spectroscopy Analysis of Botryococcene Hydrocarbons from the Green Microalga Botryococcus braunii

“…For algae to produce enough oil to meet fuel demands, large scale culturing of algae and monitoring of oil production will be required (2,3). Current analysis methods for monitoring algal oil production are complicated, time consuming, and destructive (4). Thus, a simple and nondestructive method for analyzing algal oil composition is required.…”