Energy-Transfer Phenomena in Thermoresponsive and pH- Switchable Fluorescent Diblock Copolymer Vesicles

• Published in: Langmuir Vol. 33; no. 43; pp. 12130 - 12139
• Main Authors: Maiti, Chiranjit, Dhara, Dibakar
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 31.10.2017
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.7b01891

We describe the development of a polymeric vesicle that not only selectively fluoresces at low pH, a condition prevailing in cancer cells, but also can potentially monitor the thermoresponsive release of a drug even if the drug is nonfluorescent. The developed fluorescence resonance energy transfer (FRET)-based thermoresponsive vesicular nanocarriers are composed of a new poly­(PEGMA)-b-poly­(NIPA-r-R6GMED) block copolymer, which undergoes pH-switchable superior turn on–off fluorescence characteristics. The block copolymer was synthesized using the RAFT technique, and its solution properties and self-assembly behavior were investigated by turbidity measurements, fluorescence spectroscopy, 1H NMR, dynamic light scattering, and transmission electron microscopy. The block copolymer self-assembled to form nanostructured vesicles above the critical aggregation temperature under physiologically relevant conditions. Steady-state and time-resolved fluorescence spectroscopy were utilized to study the FRET process between encapsulated hydrophobic guest C-153 (donor) and polymer-bound R6GMED units (acceptor) in the thermoresponsive vesicles. The FRET rate and efficiency were found to vary as a result of the pH-dependent changes in the quantum yield of the acceptor molecules. The occurrence of a highly efficient FRET in this polymeric vesicular nanocarrier at acidic pH, a condition similar to the cytoplasm and cell nucleus in leukemic tissues, and the ability to encapsulate hydrophilic and hydrophobic molecules and their temperature-controlled release make it potentially useful in imaging guided real-time monitoring of drug-delivery vehicles.