I have prepared curcumin-loaded solid lipid nanoparticles, but the problem was in encapsulation efficiency because I was unable to separate the untrapped drug from the curcumin-loaded solid lipid nanoparticles.
Here is a reference where there is a description of how they measured the curcumin-lipid NP encapsulation efficiency. You can adopt their process for your research: http://www.sciencedirect.com/science/article/pii/S0927776513004086