Quantifying Release from Lipid Nanocarriers by Fluorescence Correlation Spectroscopy

Understanding the release of drugs and contrast agents from nanocarriers is fundamental in the development of new effective nanomedicines. However, the commonly used method based on dialysis frequently fails to quantify the release of molecules poorly soluble in water, and it is not well-suited for in situ measurements in biological media. Here, we have developed a new methodology for quantifying the release of fluorescent molecules from lipid nanocarriers (LNCs) using fluorescence correlation spectroscopy (FCS). LNCs based on nanoemulsion droplets, encapsulating the hydrophobic Nile red derivative NR668 as a model cargo, were used. Our studies revealed that the standard deviation of fluorescence fluctuations in FCS measurements depends linearly on the dye loading in the nanocarriers, and it is insensitive to the presence of less-bright molecular emissive species in solution. In sharp contrast, classical FCS parameters, such as the number and the brightness of emissive species, are strongly influenced by ...