(667d) Fluorescent Probe as Model Solute to Study the Phase Behavior in Polymeric Nanoparticles
Nanostructured polymeric particles are effectively used as a carrier for various therapeutics . The hydrophobic solute molecules are encapsulated into the hydrophobic polymeric core using different formulation techniques . Higher drug loading in the polymeric core results in the formation of drug crystals and hence phase separation . The release of drug molecules from the nanoparticle depends on the extent of dispersion, and is diffusion and dissolution controlled at low and higher drug loading respectively . The solubility of pharmaceutical materials, and hence their bioavaiolability, also depend on the physical state. Hancock et al.  demonstrated the higher aqueous solubility for amorphous Indomethacin drug as compared to its crystalline counterpart.
In the present work, pyrene is used as a model fluorescent probe to study the phase behavior in the polymeric core. The emission spectra of pyrene displays distinct peaks of monomer and excimer molecules . The fluorescence quenching of monomer and excimer content were studied for a range of pyrene loading using various core forming polymer co-solutes. The distribution of pyrene in nanoparticle core was found to be dynamic and controlled by the miscibility between the probe and co-solutes.
Hostasol yellow, another fluorescent dye with larger molar volume compared to pyrene, was also used for the fluorescence study. Even though the fluorescence quenching was observed at higher dye loading, the spectra remains stable unlike pyrene. The Flory- Huggins theory of mixing  has been used for qualitative estimation of dye dispersity in various polymer co-solutes.
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