Direct Monitoring of Oil Production in Individual Microalgae in Situ by Raman Spectroscopy

Microalgae, producing oils that can be converted into biodiesel, are one of the promising candidates for the next generation of viable fuel to help solve the global energy crisis. However, the recent booming of research on microalgae, so far appears not benefiting from the booming of modern high-throughput, high-resolution, real-time, and in vivo biophysical techniques. Traditionally, these microalgae were treated in bulk, lyophilized or in extracted forms, making it impossible to assess the information on fundamental biological processes in the single-cell or sub-cellular level. In this work, we focus on in situ, in vivo and label-free Raman characterizations of modeled algal lipids, extracted algal oil, and most importantly, single living algae (Figure 1). Our study has demonstrated a label-free and direct method to obtain quantitative information of chain length and degree of unsaturation of the oil produced inside algae. It also connects with the important issues of the cloud point and the quality of algal biodiesel. Our single-cell, real-time, and in vivo study of algae, with various lipid-triggering mechanisms, enables the possibility of researching and engineering of the best conditions and the best species for algal growth and oil production. Figure 1. A single Neochloris oleoabundans algal cell is held by an optical trap and its Raman spectrum is obtained. Black arrows are pointing at the Raman bands of oil identification. A dashed arrow is pointing at the Raman band of unsaturation (C=C bonds) of the oil inside the alga.&'