Browsing by Subject "Conjugated polymer"
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Item Open Access Stimuli-responsive conjugated polymer nanoparticles as simple theranostic platforms = Basit teranostik platformlar olarak uyaranlara hassas konjuge polimer nanoparçacıklar(Bilkent University, 2014) Özgün, AlpIn this study, green and near-infrared emitting stimuli responsive conjugated polymer nanoparticles that can be utilized simultaneously for chemotherapeutic drug delivery and bioimaging were synthesized. The nanoparticles are sensitive to low pH values of tumor microenvironment or elevated redox potential of some tumor types. These theranostic platforms could be used for in-vivo imaging and perform controlled-drug release triggered by an appropriate stimulus. For this purpose, green emitting polymer with fluorene and benzothiadiazole alternating units in the backbone and a conjugated polymer emitting in the red-NIR region based on thiophene and benzothiadiazole alternating units in the backbone were synthesized and characterized. Nanoparticles of these polymers (CPNs) were prepared by a simple method called nanoprecipitation where hydrophobic polymer chains collapse onto each other in aqueous media, trapping any other hydrophobic drug molecules (anticancer agent camptothecin in our case) in the environment inside the polymer matrix. Nanoprecipitation process was optimized for each polymer to obtain maximum drug encapsulation rate and a narrow nanoparticle size distribution under 100 nm. Resulting CPNs were stable for a long time in PBS buffer, water, bovine serum albumin and human plasma. SEM images showed spherical particles with a narrow diameter distribution. In vitro drug release studies, pH responsive CPNs showed faster drug release in more acidic media. Redox sensitive red polymer on the other hand showed a cleavage of disulfide bond in its structure in the presence of stimulus. To evaluate the cytotoxicity of drug loaded and blank CPNs RT-CES (real-time cell electronic sensing) assays with HuH-7 cell line have been carried out. While blank CPNs show an insignificant temporary cytotoxicity, camptothecin loaded nanoparticles match or outperform the growth inhibition effect of free camptothecin. Fluorescence microscopy images of HuH-7 cells incubated with CPNs clearly show CPNs that are internalized by cells. In conclusion, it was demonstrated that conjugated polymers could be used to fabricate theranostic platforms without the need for an additional imaging agent and their structures can be engineered to obtain stimuli responsive smart drug delivery systems. These results promise simple and easily fabricated smart systems that can selectively carry anticancer agents to tumors while enabling monitoring of drug distribution and inexpensive tumor imaging without using any harmful rays on the highly energetic side of the electromagnetic spectrum.Item Open Access Synthesis of novel photoactive nanoparticles towards phototherapy(Bilkent University, 2021-09) Duah, Ishmeal KwakuNanomaterial-based compounds are attracting a lot of interest because many functionalities such as photoactive units, drugs and targeting groups can be combined on one platform to fight against infectious diseases and cancer. Recently, conjugated polymer-based nanomaterials have proven to be effective photosensitizers for antibacterial and photodynamic cancer therapies owing to their unique electronic and optical properties, including high singlet oxygen generation capacity, strong light-harvesting ability and its tunable optical spectrum. In this study, novel cross-linked conjugated polymer nanoparticles-based photosensitizers namely conjugated polymer-porphyrin nanoparticles (CPPN) and cross-linked conjugated polymer nanoparticles (PCP) were synthesized. The nanoparticles were prepared via nanoprecipitation using cucurbit[6]uril-(CB6)-catalyzed azide-alkyne cycloaddition (CB6-AAC) reaction. Conjugated polymer-porphyrin nanoparticles (CPPN) are advantageous than micelles incorporating porphyrin systems. For micelles containing porphyrin systems, the phototherapy effect of the porphyrin can only be seen after the porphyrin is released by conditions such as a change in pH, which is not the case for conjugated polymer-porphyrin nanoparticles (CPPN). The nanoparticles demonstrated high reactive oxygen species (ROS) generation efficiency which is evident in the antibacterial and anticancer photodynamic therapy (PDT) experiments. From the antibacterial photodynamic therapy experiment, when Gram-negative (Escherichia coli, E. coli) and Gram-positive (Bacillus subtilis, B. Subtilis and Staphylococcus aureus, S. aureus) bacteria were incubated with CPPN (20 µg/mL) and irradiated with white light (22 mW/cm2) for 10 min, more than 3.5-log reduction in colony-forming units (CFUs) was recorded for CPPN. Furthermore, when E. coli and B. subtilis were treated with PCP (24 µg/mL) and illuminated with light, about 3-log killing efficiency was recorded. However, in the dark, the nanoparticles demonstrated minimal dark cytotoxicity against the model bacteria. In addition, the anticancer photodynamic effect of CPPN and PCP on MCF-7 breast cancer cells was investigated. When MCF-7 breast cancer cells were treated with PCP in the dark and under light irradiation, almost all cells were alive for both cases. It may be that PCP could not generate enough reactive oxygen species to kill the cells. When MCF-7 breast cancer cells were treated with CPPN in the dark, the cell viability was 96% and upon irradiation with light for 20 minutes, the cell viability decreased to about 4%. Moreover, conjugated polymer-porphyrin-gold nanoparticles (CPPN-Au) and cross-linked conjugated polymer-gold nanoparticles (PCP-Au) nanoparticles were prepared, but due to the instability of the nanoparticles, they could not be used in phototherapy.Item Open Access Synthesis of oligomers, polymers and cucurbituril- based polyrotaxanes towards polymer light emitting diode and photodynamic therapy application(Bilkent University, 2014-06) Idris, MuazzamIn the first part of this study, porphyrin-thiophene monomers, oligomers and polymer are synthesized for photodynamic therapy application. Water solubility and the ability of a photosensitizer to generate singlet oxygen for tumor destruction are important conditions for ideal photosensitizer in photodynamic therapy application. For this purpose, water soluble pendent groups are attached to the porphyrin monomers before coupling with thiophene monomer to form oligomers and polymer. The presence of sulfur atom in thiophene facilitates intersystem crossing due to spin-orbit coupling and thus will increase singlet oxygen generation. Consequently, the ability of singlet oxygen generation of the polymer is found to be higher than oligomers followed by monomers. In the second part of the thesis, the effects of cucurbit[n]uril on photophysical, electrochemical and thermal properties of ionic conjugated polymers in water are described. Conjugated polymers are well known for their interesting optical properties and are used in the area of light emitting diodes. However, their stacking nature reduces their fluorescent quantum yields and thus limits their further applications. If the interactions among the polymers chains are reduced or the polymer backbones are insulated in some means, the emission efficiency of the polymers could be enhanced. For this purpose, two different green emitting fluorene-thiophene based polymers (29 and 33) and their cucurbituril based polyrotaxanes counterparts (30 and 34) are synthesized through Suzuki Coupling. In both polyrotaxane 30 and 34, enhancement in optical properties was observed showing fluorescent quantum yields of 0.46 and 0.55 in water respectively comparing to polymers 29 and 33 which has only 0.10 and 0.35 in water respectively. Their optical and electroluminescent properties were further utilized by fabricating devices as multilayer white polymer light emitting diodes (PLEDs). The synthesized molecules are characterized by 1H-NMR, 13C-NMR, ESI mass spectrometry, UV-VIS, photoluminescence, time resolved fluorescence spectroscopy, FT-IR, elemental analysis gel permeation chromatography, size exclusion chromatography, thermogravimetric analysis and cyclic voltammetry.Item Open Access X-ray photoelectron spectroscopic investigation of conducting polymer blends(Springer, 1996) Süzer, Ş.; Toppare, L.; Hallam, K. R.; Allen, G. C.Electrochemically prepared films of conducting polymers of polypyrrole and polythiophene and their blends with polyamide have been investigated by X-ray photoelectron spectroscopy. In the N1s region of the spectra of films containing polypyrrole the peak corresponding to N+ at 402.0 eV is separated from that of neutral N. The intensity of the N+ peak can be correlated with the electrical conductivity of the films and the spectroscopically derived ratio of F/N+ is close to 4 indicating that one BF4 - dopant ion is incorporated for every oxidized nitrogen center. In the spectra of films of polythiophene and its blends peaks corresponding to S and S+ can not be resolved but again the F/C ratio correlates with the electrical conductivity. © Springer-Verlag 1996.