Encapsulation Efficiency (EE) Determination

EE, an important parameter for quality control, is of great significance in developing liposome-based delivery systems. The EE determination was based on the high speed centrifugation method. Briefly, 100 μl Cur-LPs was centrifuged at the low speed (3000 rpm, 5 min) to precipitate non-dissolved free curcumin, and 50 μl supernatant was subjected to high-speed centrifugation (16 krpm, 10 min) to separate Cur-LPs from the tiny dissolved curcumin. The pellets were re-suspended in 500 μl PBS (i.e., 10-fold dilution), an aliquot of 10 μl of which was mixed with 300 μl ethanol by vortex and sonication for 30 s. The fluorescent intensity of curcumin in the resultant solution was determined (excitation wavelength (Ex), 458 nm; emission wavelength (Em), 548 nm) and presented as F _e, i.e., the fluorescent intensity of encapsulated curcumin. Another 50 μl of fresh Cur-LP containing encapsulated and free curcumin was also diluted by 10-fold with PBS, and 10 μl of the diluted solution were mixed with 300 μl ethanol. The fluorescent intensity of the resultant solution was measured and presented as F _t, i.e., the fluorescent intensity of total curcumin. The EE was therefore calculated with the following equation: EE = F _e/F _t.