The increase in intracellular neutral lipid during the growth
cycle of isolated microalgae strains was measured via fluorescence
intensity of NR stained cultures [12] simultaneously to cell
growth. 10 mL of NR was added to 3mL of algal suspensions
which was then vortexed for 1min prior to incubation for 10min
in darkness at room temperature. NR emits a yellow-gold fluorescence
when dissolved in neutral lipid which is the best
substrate to produce biodiesel [13,14]. Fluorescence intensity of
a stained suspension of microalgae was measured at an excitation
and emission wavelength of 480 nm and 575 nm respectively
using an LS-55 fluorescence spectrometer (PerkineElmer
Corp.) normalized at an optical density of 0.2 at wavelength
680 nm (OD680). The microalgae suspension without NR,
considered as auto-fluorescence, was also measured and subtracted
from that measured as NR fluorescence.