Phasor-Fluorescence Lifetime Imaging Microscopy Analysis to Monitor Intercellular Drug Release from a pH-Sensitive Polymeric Nanocarrier.

The design of highly efficient drug carriers, and the development of appropriate techniques to monitor their mechanism of action and therapeutic effect, are both critical for improving chemotherapy. Herein, a polymeric nanoparticle, PAH-Cit/DOX (poly(allylamine)-citraconic anhydride/doxorubicin), was synthesized and used as a nanodrug system for the efficient delivery and pH-responsive release of doxorubicin (DOX) into cancer cells. The PAH-Cit/DOX nanoparticles were stable at physiological pH but effectively released DOX under weakly acidic conditions. The release efficiency was 90.6% after 60 h of dialysis in phosphate-buffered saline at pH 5.5. Confocal images showed the rapid movement of the drug from the cytoplasm to the nucleus, indicating the effective drug release MCF-7 cells. Notably, the combination of fluorescence lifetime imaging microscopy (FLIM) and phasor analysis (phasor-FLIM) provides an approach to monitor the dynamic change of DOX fluorescence lifetime in intercellular environments. Phasor-differentiated lifetime pixel intensity in FLIM images was quantified and used to evaluate the DOX release from nanocarriers, making it possible to detect the dynamics of intracellular release and transport of DOX.