Environment-responsive aza-BODIPY dyes quenching in water as potential probes to visualize the in vivo fate of lipid-based nanocarriers

Environment-responsive near-infrared (NIR) aza-BODIPY dyes capable of fluorescence quenching in water were explored to visualize the in vivo fate of model lipid-based nanocarriers, solid lipid nanoparticles (SLNs). The water-quenching effect of the dyes was confirmed to be sensitive and remained stable for at least 24 h. In vitro lipolysis measured by fluorescence quenching completed within 20 min, which was in correlation with alkaline compensation results. In vivo live imaging indicated predominant digestion of SLNs within 2 h and complete digestion within 4 h, which correlated well to in vitro data. Rekindling of quenched dyes by mixed micelles was observed in vitro, but not in vivo. In sharp contrast, SLNs encapsulating another NIR dye DiR showed persistent fluorescence both in vitro and in vivo despite significant lipolysis. It was envisaged that water-quenching fluorescence dyes can be used as probes to monitor the in vivo fate of lipid-based nanocarriers. Lipid-based drug delivery systems can provide an excellent nanocarrier platform for the delivery of poorly water-soluble drugs. Nonetheless, the mechanism of oral absorption and subsequent kinetics is poorly understood. In this article, the authors studied the novel use of near-infrared (NIR) aza-BODIPY dyes to visualize the fate of these lipid-based nanocarriers. The positive finding means that this approach may be useful for in-vivo monitoring of lipid-based nanocarriers.