Study On Cellular Application Of Water-Soluble Conjugated Polymer Nanocomposites

The water-soluble conjugated polymers (WS-CPs) are a unique class of polyelectrolytes with π-conjugated backbone and charged side chains. Thanks to the highly electron-delocalized backbones inheriting from organic soluble conjugated polymers, WS-CPs possess distinguished capability to harvest and emit light energy, manifesting as superior optoelectronic properties. Simultaneously, the electrostatic-mediated physicochemical behaviors in aqueous media derived from polyelectrolytes allow WS-CPs to interact with various biological substances. With these structure-related functional advantages, WS-CPs are born to be valuable fluorescence probes for biological applications. In this thesis, we study on the cellular applications of nanocomposites based on two water-soluble conjugated polymers, i.e. cationic poly{9,9-bis{3’-[(N,N-dimethyl)-N-ethylammonium]propy 1}-2,7-fluorene-alt-1,4-dithiophene-2,1,3-benzothiadiazole dibromide} (TBtPFN) and anionic poly[9,9-di(3-sulfonatopropyl)-2,7-fluorenyl-alt-4,7-(2,1,3-benzothiadiazole)] (BtPFS).First of all, we obtained fluorescent nanocomposites (TBtPFN/cMWNT and BtPFS/TBtPFN/cMWNT) via electrostatic deposition of WS-CPs on the negatively charged surface of carboxylated multi-walled carbon nanotubes (cMWNTs). The electrostatic assembly process is affected by the pH values and ionic strength of the aqueous solution. Subsequently, we demonstrated the energy transfer between the two adjacent WS-CP layers. Moreover, the coating of WS-CPs endows the nanocomposites enhanced protein-repellent property, giving them a tempting prospect for in vivo application.Secondly, we demonstrated that the obtained nanocomposites inherit intrinsic optical properties of WS-CPs and characteristic Raman vibration modes of MWNTs, providing a fluorescence-Raman dual-imaging method for intracellular tracking and locating of MWNT nanocomposites. The surface charge discrepancy gives rise to different intracellular distribution patterns of TBtPFN/cMWNT and BtPFS/TBtPFN/cMWNT nanocomposites.What is more, we investigated the cellular uptake pathways and clarified the interaction mechanism of the fluorescent nanocomposites and cancer cells (Bel-7402). The internalization of positively charged TBtPFN/cMWNT is mainly mediated by clathrin-mediated endocytosis and secondarily mediated by passive insertion and diffusion of CNTs; the internalization of negatively charged BtPFS/TBtPFN/cMWNT is mediated by the combinations of several cellular uptake mechanisms including caveolin-mediated endocytosis, macropinocytosis, and passive insertion and diffusion of CNTs, which seems to be the most important pathway. Additionally, the surface charge impacts the cellular uptake efficiency and cytotoxicity of the nanocomposites. These results are attractive for further application of carbon nanotubes as biological carriers.On the other hand, we developed a fluorescent drug nanosystem (APB) by introducing anionic WS-CPs (BtPFS) into alginic acid-poly(2-(diethylamino)ethyl methacrulate) nanoparticles (ALG-PDEA NPs). The APB nanoparticles shows excellent biocompatibility and cellular uptake efficiency. Subsequently, we evaluated the in vitro antitumor efficiency of both blank and doxorubicin (DOX) loaded ALG-PDEA nanoparticles (APB-DOX NPs).