Design and Synthesis of Organic Semiconducting Oligomer Nanoprobes for Bioimaging and Biosensing Applications

Author:Yin Chao

Supervisor:fan qu li


Degree Year:2017





As a new class of optical nanoagents,semiconducting polymer nanoparticles(SPNs)have been utilized for bio-imaging,bio-sensing and therapy beacuse of their excellent optical properties and biocompatibility.Recently,we have found that SPNs can convert photon energy into heat in a way that can be more efficient than many other nanomaterials such as gold nanorods,permitting superior photothermal and photoacoustic imaging applications.However,there are still some drawbacks in the structure design and applications for the existing SPNs: 1.Preparation of water-miscible SPNs is limited to nanoprecipitation that incorporate semiconducting polymers into amphiphilic block copolymers via self-assembly process.Therefore,most existing SPNs have the potential issues of slow dissociation during blood circulation,resulting in changed optical properties and poor biodistribution.2.The large molecular weight of semiconducting polymers made SPNs difficult to be cleared out from the body.3.SPNs-based activatable nanoprobes are still limited.Therefore,we aim to develop novel semiconducting oligomer nanoprobes with high structural stability and photostability,good biodegradability as well as recognition capability toward specific biomolecules.The thesis can be divided into five sections:1.Oligo(p-phenyleneethynylene)-Based Semiconducting Fluorescent Nanoparticles: Preparation,Photophysical Properties and Two-Photon Cell ImagingIn this section,amphiphilic organic asymmetrically oligo(p-phenyleneethynylene)(OPE)conjugated molecules were designed and synthesized.Due to the hydrophilic-hydrophobic nature of the OPE conjugated molecules,monodispersed fluorescent nanoparticles were obtained easily by self-assembly in aqueous solution,and their concentration-dependent morphology changes were further investigated.The structural stability of the nanoparticles was higher than those prepared from nanoprecipitation method as OPE segment was introduced into the amphiphile via covalent linkage.Cellular experiments showed good biocompatibility for the nanoparticles which can be employed as novel nanoprobes for bioimaging and drug delivery.2.Fluorescent Oligo(p-phenyleneethynylene)Contained Amphiphiles-Encapsulated Magnetic Nanoparticles for Targeted Magnetic Resonance and Two-Photon Optical Imaging in vitro and in vivoFolate receptor-targeted multifunctional fluorescent magnetic nanoparticles(FMNPs)composed of cores containing iron oxide nanocrystals and amphiphilic oligo(p-phenyleneethynylene)shells with multimodal imaging capability were successfully prepared through convenient hydrophobic encapsulation approach.The iron oxide nanoparticles in the core provided T2-weighted magnetic resonance imaging(MRI),whereas the amphiphilic oligomers on the surface of the nanoparticles introduced good water-solubility,biocompatibility,excellent fluorescent properties and cancer-targeting.TEM showed the spherical morphology of the nanoparticles with the average diameter of 34.4 ± 2.5 nm.These nanoparticles exhibited superparamagnetic properties with saturation magnetization(Ms)of 23 emu/g and transverse relaxivity rate of 140.89 m M-1 s-1.Z-scan test demonstrated the remarkably large two-photon absorption(2PA)cross section of 2362 GM.In vitro and in vivo two-photon fluorescence and MRI results demonstrated that the FMNPs were able to preferentially accumulate in tumor tissues to allow dual-modal detection of tumors in a living body.3.Near-Infrared Absorbing Semiconducting Oligomer Nanoparticles for Photoacoustic and Fluorescence ImagingIn this study,we report structurally stable near-infrared(NIR)-absorbing organic semiconducting nanoparticles for in vivo photoacoustic(PA)and fluorescence imaging.The nanoparticles are self-assembled from an amphiphilic semiconducting oligomer(ASO)that has a hydrophobic semiconducting oligomer backbone attached by hydrophilic poly(ethylene glycol)(PEG)side chains.ASO has higher structural stability and brighter PA signals as compared with its counterpart nanoparticles(SON)synthesized by nanoprecipitation.The small size and PEG-passivated surface of ASO allow it to passively target to and efficiently accumulate in the tumor of living mice,permitting tumor imaging with high signal-to-background ratios.Our study provides new NIR-absorbing organic nanoparticles for PA and fluorescence imaging,which also have the potential to be used as drug carrier for theranostics.4.Phenothiazine-Based Organic Nanoprobe Cocktails for Multilocal and Multicolor Fluorescence Imaging of Reactive Oxygen SpeciesIn this work,two semiconducting oligomers and two amphiphilic block copolymers are synthesized and used as the building blocks for the construction of nanoprobes LNP and MNP.Both LNP and MNP are sensitive to Cl O-but show different multicolor responses toward Cl O-: green to blue for LNP,and red to orange for MNP.The mixture of these nanoprobes forms a nanococktail that allows for simultaneous imaging of elevated level of Cl O-in lysosome and mitochondria according to fluorescence color variations under selective excitation of each nanoprobe.Fluorescent quantification showed the average Cl O-concentrations in lysosomes and mitochondria in activated macrophage cells were estimated to be 9.0 and 8.0 μM,respectively.Such estimated concentrations were consistent with the values reported in literatures.5.Degradable Semiconducting Oligomer Nanoprobe for Ratiometric Photoacoustic Imaging of HypochloriteThis study proposed a self-assembly approach to develop activatable and degradable photoacoustic(PA)nanoprobes for in vivo imaging of Cl O-.A near-infrared absorbing amphiphilic oligomer was synthesized to undergo degradation in the presence of a specific ROS(Cl O-),which integrates a π-conjugated but Cl O-oxidizable backbone with hydrophilic PEG side chains.This molecular architecture allows the oligomer to serve as a degradable nanocarrier to encapsulate the ROS-inert dye(NIR775)and self-assemble into structurally stable nanoparticles.The self-assembled nanoprobe exhibits sensitive and specific ratiometric PA signals toward Cl O-,permitting ratiometric PA imaging of Cl O-in the tumor of living mice.