Conjugated Polymer Nanoparticles Enhanced Two Photon Excitation Properties In Biological Applications

Cancer is the main threat to human health and life.Even though the conventional cancer treatment options such as surgery,radiation and chemotherapy and immunotherapy has made a lot progress in the past years,we still need to develop new ways to treat tumor.Photodynamic therapy（PDT）is a non-invasive technique that is approved for the treatment of carcinoma.Briefly,upon activation by light of a particular wavelength,photosensitizer（PS）will react with molecular triplet oxygen and generate cytotoxic reactive oxygen species,mostly singlet oxygen,for cell apoptosis.Generally no cytotoxicity will be generated by PDT unless all three key components exist:light source,PS and tissue oxygen.Thus,PDT is advantageous over traditional cancer treatments like chemotherapy for its low toxic effects.Two-photon excitation photodynamic therapy（2P-PDT）using near-infrared light as excitation source offers many advantages such as its potentials for deep tissue treatment,less interference by absorption and scattering from surrounding biological environment,and minimal invasive feature.Over the past few decades photodynamic therapy has been proven to be effective in cancer due to its minimal invasiveness,repeatability without cumulative toxicity,excellent functional and great precision in treatment.Nevertheless,the clinical applications of 2P-PDT are limited by the low two-photon absorption（2PA）cross sections（δ）of current clinically approved PSs.In addition to generating cytotoxic singlet oxygen for killing cancer cells,the inherent photoluminescence from PS is of great importance to fluorescence imaging applications.However,it is difficult to realize both high singlet oxygen generation efficiency and high brightness from a molecular PS because fluorescence emission（S₁→S₀）and singlet oxygen generation（S₁→T）are two competing processes after the molecular PS is brought to the excited singlet state（S₁）.The research demonstrated in this thesis focuses on preparing a nano-sized PS for achieving simultaneously near-infrared imaging and 2P-PDT activities,especially on the PSs based conjugated polymer.Conjugated polymer nanoparticles have the large extinction coefficient,high fluorescence quantum yield and great biocompatibility.They can be utilized as two-photon light harvesting materials to improve singlet oxygen production of photosensitizer by fluorescence resonance energy transfer（FRET）for the outstanding photo-physical properties.In chapterⅡ,we developed a multifunctional conjugated polymer nanoparticles as nano-sized PSs with highly efficient 2P-PDT and two-photon imaging activities by encapsulating both tetraphenylporphyrin（TPP）and a red-emitting dye（TPD）into hydrophobic conjugated polymer（PPBF）.Conjugated polymer PPBF was chosen as a two-photon light-harvesting material due to its large 2PA cross sections.TPP and TPD were chosen as the energy acceptors.The enhanced imaging and PDT effect is realized by a FRET strategy from conjugated polymer PPBF to TPP and TPD.Two-photon-excitation（2PE）emission of TPP and TPD was enhanced by up to¹61 and²3 times,respectively.The singlet oxygen generation and cytotoxicity evaluation results clearly showed that the 2P-PDT efficiency of these FA-PPBF/TPP/TPD NPs are significantly improved compared with those NPs without PPBF,potentially up to about 149 times.Through surface-functionalized folate groups,the obtained FA-PPBF/TPP/TPD NPs show a specific selectivity in targeting KB cancer cells via folate receptor mediated interactions.These nanoparticles could act as novel2PE conjugated polymer nanoparticles with combined advantages of low dark cytotoxicity,targeted 2P-PDT with high selectivity,and simultaneous 2PE fluorescence imaging capability.In chapterⅢ,we developed a new PSs based gold nanorod（AuNR）by incorporation of two kinds of light harvesting materials（Au NR and conjugated polymer）with TPP.CPNs is short for conjugated polymer nanoparticles.The obtained AuNR@SiO₂-CPNs can enhance further the optical properties of TPP due to the exsistence of AuNR.Silica shells with different thicknesses were coated on AuNR to tune the separation distances between CPNs and AuNR.By tunning the separation distances between CPNs and AuNR to develop a nano-sized PSs achieving highly enhanced singlet oxygen generation capability and highly efficient 2P-PDT.