Morphology-Tunable Fluorescent Nanoparticles: Synthesis, Photophysical Properties and Two-Photon Cell Imaging

A novel water-soluble fluorescent amphiphile based on amino polyethylene glycol (PEG-NH₂) substituted oligo(p-phenyleneethynylene) (OPE) was designed and synthesized successfully. Taking anion OPE amphiphile as a comparison, the photophysical features were investigated through ultraviolet absorption (UV) and photoluminescence (PL) analyses. Due to the hydrophobic-hydrophilic property of the OPE conjugated molecule, self-assembled nanoparticles with the size ranging from 19.6 to 93.5 nm along with the change of morphology from grain to strawberry were conveniently prepared via adjusting concentrations of OPE aqueous solution. Interestingly, after aging for a period of time, homogeneous hollow nanospheres were spontaneously constructed with a diameter of about 200 nm. Cytotoxicity test and cellular uptake behavior of the nanoparticles were further investigated to evaluate their potential biomedical applications. Subsequently, the promising applications of two-photon cell imaging were explored using human pancreatic cancer cells (PANC-1 cells), which indicated that the nanoparticles were mainly located within the cell cytoplasm. Monodisperse single nanoparticles can be formed by self-assembly firstly, and then gathered to large aggregates with the increase of amphiphilic OPE concentration. Finally, these aggregates would crimp to form homogeneous hollow nanospheres through aging the solution for one week.