Supramolecular fluorescent nanoparticles functionalized with controllable physical properties and temperature-responsive release behavior

Supramolecular fluorescent nanoparticles (SFNs), a combination of hydrogen-bonded supramolecular macromers and fluorescent pyrene dyes, can spontaneously self-assemble into thermosensitive micelles in an aqueous environment; the resulting micelles exhibit unique thermo-responsiveness and tunable phase transition behavior, making them highly attractive for the development of next-generation biomedical imaging tools and smart drug delivery applications. Herein, we developed a low-molecular-weight supramolecular polymer, adenine end-capped difunctional polypropylene glycol (BA-PPG), containing an adenine multiple hydrogen bonding moiety that effectively encapsulates pyrene molecules to generate the desired nanoparticle size, pyrene-loading content, and fluorescence properties in aqueous solution. Importantly, pyrene-loaded BA-PPG micelles act as a stable nanocarrier to greatly improve the pyrene-entrapment stability and generate high green-colored excimer emission under physiological conditions. Increasing the temperature above the lower critical solution temperature (45 °C) triggered a rapid release of the encapsulated pyrene from the loaded micelles due to the dissociation of the dynamic hydrogen bonds between adenine moieties, leading to the release of pyrene into aqueous solution and a gradual decrease in pyrene excimer emission. Given its simplicity of fabrication, low cost, high efficiency and multi-functionality, this newly-developed temperature-responsive micelle offers a new pathway for the development of high-efficiency SFNs.