PEG-Phospholipids Coated Quantum Rods as Amplifiers of the Photosensitization Process by FRET

Singlet oxygen (¹O₂) generated upon photostimulation of photosensitizer molecules is a highly reactive specie which is utilized in photodynamic therapy. Recent studies have shown that semiconductor nanoparticles can be used as donors in fluorescence resonance energy transfer (FRET) process to excite attached photosensitizer molecules. In these studies, their unique properties, such as low nanoscale size, long-term photostability, wide broad absorbance band, large absorption cross section, and narrow and tunable emission bands were used to provide advantages over the traditional methods to produce singlet oxygen. Previous studies that achieved this goal, however, showed some limitations, such as low FRET efficiency, poor colloidal stability, nonspecific interactions, and/or complex preparation procedure. In this work, we developed and characterized a novel system of semiconductor quantum rods (QRs) and the photosensitizer meso-tetra(hydroxyphenyl) chlorin (mTHPC), as a model system that produces singlet oxygen without these limitations. A simple two-step preparation method is shown; Hydrophobic CdSe/CdS QRs are solubilized in aqueous solutions by encapsulation with lecithin and PEGylated phospholipid (PEG-PL) of two lipid lengths: PEG₃₅₀ or PEG₂₀₀₀. Then, the hydrophobic photosensitizer mTHPC, was intercalated into the new amphiphilic PEG-PL coating of the QR, providing a strong attachment to the nanoparticle without covalent linkage. These PEGylated QR (eQR)-mTHPC nanocomposites show efficient FRET processes upon light stimulation of the QR component which results in efficient production of singlet oxygen. The results demonstrate the potential for future use of this concept in photodynamic therapy schemes.