Color-Tunable Amphiphilic Segmented π-Conjugated Polymer Nano-Assemblies and Their Bioimaging in Cancer Cells

Abstract

We report a unique color tunable amphiphilic segmented π-conjugated polymer design and their π-stack driven diverse self-assembled nanostructures and demonstrate their application as a new classes of aqueous luminescent nanoparticle probes for bioimaging in cervical and breast cancer cells. Oligo-phenylenevinylene (OPV) was employed as rigid luminescent π-core and oligo-ethyleneoxy chains were used as flexible spacers to construct new amphiphilic segmented π-conjugated polymers by Witting–Horner polymerization route. The rigidity of the π-core was varied using tricyclodecanemethyleneoxy, 2-ethylhexyloxy or methoxy pendants and appropriate π-core geometry was optimized to achieve maximum aromatic π-stacking interactions. Solvent-induced chain aggregation of the polymers exhibited a morphological transition from one-dimensional helical nanofibrous to three-dimensional spherical nanoassemblies in good/bad solvent combinations. This morphological transformation was accompanied by the fluorescence color change from blue-to-white-to-yellow. CIE color coordinates exhibited x = 0.25 and y = 0.32 for the white light followed by the collective emission from aggregated and isolated OPV chromophores. Electron and atomic microscopes, steady state photophysical studies, time-resolved fluorescent decay analysis, and dynamic light scattering method enabled us to establish the precise mechanism for the self-assembly of segmented OPV polymers. The polymers produced stable and luminescent aqueous nanoparticles of <200 nm diameter in water. Cytotoxicity studies in cervical and breast cancer cells revealed that these new aqueous luminescent polymer nanoparticles are highly biocompatible and nontoxic to cells up to 60 μg/mL. Cellular uptake studies by confocal microscope further exposed that these nanoparticles were internalized in the cancer cells and they were predominantly accumulated in the nucleus. The present investigation opens up new amphiphilic segmented π-conjugated polymer design for producing diverse supramolecular assemblies and also demonstrates their new application as biocompatible fluorescent nanoprobes for imaging in cancer cells.