Inside algal cells, the dye partitions to cytoplasmic lipid droplets where is becomes fluorescent. This dye has been shown to pass through the cell wall of many different species of algae when dissolved in aqueous/DMSO solutions. It is relatively photostable, highly fluorescent in non-polar hydrophobic environments, yet very poorly fluorescent in aqueous solutions. Purified Nile red is a lipid soluble dye that has many characteristics that make it amenable for use as a means to detect neutral lipids.

Nile red (9-(Diethylamino)-5H benzo phenoxazin- 5-one) is a red phenoxazone dye present in trace amounts that is responsible for the metachromatic coloring of tissue lipids when staining procedure that use Nile blue are employed. However, under unfavorable or restricted growth conditions microalgae accumulate neutral lipids in lipid droplets located in the cytoplasm. glycolipids and phospholipids), which enrich chloroplast and cellular membranes. Under favorable and unlimited growth conditions microalgae produce primarily polar lipids (e.g. Neutral lipids are composed primarily of triacylglycerol esters (TAG). Like higher plants, microalgae produce both neutral and polar lipids. Microalgae are a diverse group of lower plant photosynthetic microorganisms that live in fresh or marine water environments and are able to use solar energy to fix carbon into biomass and synthesize lipids. As a result of global climate change and the ever rising price of transportation fuels, recent interest has focused on the ability of algae to produce lipids that are easily converted to biodiesel. Microalgal cultures have been used to produce natural products that have been derived into pharmaceuticals and nutraceuticals for a number of years. Here we describe the use of the Synergy™ H4 Multi-Mode Microplate Reader to monitor lipid levels in algal cultures using fluorescence. The fluorophore Nile red has been shown to be quite useful in detecting neutral lipids in many different microalgae. Lipid production by algal cultures has become an important area of research in biodiesel and other natural products. and Keri Raymond, Applications Department, BioTek Instruments, Inc., Winooski, VT

Nile red powder