Design And Synthesis Of Water-soluble Conjugated Compounds And Research On Sensing, Imaging And Antibacterial Applications

Water-soluble conjugated compounds(polymers/oligomers)have the characteristics of photosensitivity,easy modification and good water-solubility.In addition,conjugated polymers have the signal amplification ability due to its "molecular wires" structure.In recent years,they have been applied widely in biosensor,cell imaging,drug release,photodynamic treatment,etc.In this thesis,several new water-soluble conjugated compounds have been synthesized and new biosensors have been established based on these compounds.Herein,"self-assembly" strategy was introduced into the biosensing and antibacterial applications.Highly selective detection of ATP and rapid imgaing of endogenous nitric oxide have been achieved.Furthermore,broad-spectrum and greatly high antibacterial activities at nanogram permilliliter concentrations were gained under irradiation,and specific antibacterial activity against methicillin-resistant S.aureus also were obtained in dark.The results are as follows:1.A new conjugated polymer-based combination probe for ATP detection using a multisite-binding and FRET strategyWe designed and synthesized two conjugated polymers including phenylboronic acid(PBA)-modified PPE-PBA and quaternary ammonium-modified PFP-NMe3+,which were used as a new combination probe to sense ATP.The new neutral PPE-PBA can recognize ribose of ATP via covalent bonding and PFP-NMe3+ can interact with the negatively charged phosphates of ATP via electrostatic interaction.The efficient FRET will occur when ATP is present and it brings two CPs close to the multi-recognition sites.The significant enhancement of the fluorescence ratio can be used to quantify the concentration of ATP.The new CP-based combination probe based on the multisite binding and "self-assambly" strategy could sensitively and selectively distinguish ATP from interferents,such as adenosine,ADP,AMP,NNPs,saccharides,etc.This study should provide a novel strategy for designing composite CP-based ratiometric probes to detect chemical and biological analytes via "self-assembly" strategy.2.An ultra rapid detection of endogenous nitric oxide in cells and in microorganisms based on fluorescent conjugated polymers probeA cationic water-soluble conjugate polymer PBFB-PDA-NMe3+ modified with o-phenylenediamine was synthesized to achieve rapid imaging of endogenous nitric oxide in A549 cells and S.aureus biofilms.The introduction of o-phenylenediamine groups into PBFB-PDA-NMe3+ can quench the fluorescence of the main chain of the polymer via photoinduced electron transfer(PET)and on the other hand,it can specifically capture and react with nitric oxide to form benzotriazole,blocking the PET process to restore the fluorescence of PBFB-PDA-NMe3+.The probe has an ultra-fast response to nitric oxide,allowing detection within 60 seconds with a limit of detection of 1.3 μM.The biocompatibility of this probe is good.After incubation with 5 μM probe for 24 hours,cell viability of A549 is still above 85%.Based on these studies,we utilized this probe to image endogenous nitric oxide in A549 cells and S.aureus biofilms and found that the ideal imaging results were obtained in 15 minutes,which is more rapid than those methods reported in literatures.Furthermore,PBFB-PDA-NMe3+ is mainly distributed in the cytoplasm of A549 cells with co-localization imaging.In addition,PBFB-PDA-NMe3+ also has potent photodynamic bactericidal activity against S.aureus.After irradiating S.aureus for 30 min,about 96%bacterial cells were dead at the concentration of 150 nM PBFB-PDA-NMe3+.This new probe is potential to monitor cellular signal transduction and could be used for NO-related disease diagnosis.3.Cationic oligo(thiopheneethynylene)with broad-spectrum and high antibacterial efficiency under white light and specific biocidal activity against S.aureus in darkA new water-soluble conjugate oligomer OTE was designed and synthesized and its biocidal activities against pathogens and plant pathogenic bacteria were studied.The maximum absorption wavelength of OTE was 396 nm.Under white light irradiation,OTE presents broad-spectrum and greatly high antibacterial activities at nanogram permilliliter concentrations.The IC50 of OTE for S.aureus,S.epidermidis,E.coli and R.solanacearum were 8,13,24 and 52 ng/mL,respectively,which are lower than that of other PDT agents.Interestingly,OTE shows the specific and very strong dark killing capability against S.aureus at the concentration of 180 ng/mL for 30 min,which is the highest efficiency biocide against S.aureus without the need of irradiation to date.The antibacterial mechanism investigated demonstrated that reactive oxygen species or singlet-oxygen generated by OTE kills bacteria irreversibly upon white light irradiation,and OTE as a v-type oligomer exerts its toxicity directly on destroying bacterial cytoplasmic membrane in the dark,leading to leakage of bacterial cell contents.This research provides a platform for highly effective and specific antibacterial performance.4.Conjugate oligomer-based self-assembly hydrogel with specific antibacterial activity against methicillin-resistant S.aureus without irradiationA novel compound OTE-D-Phe was synthesized by modifying the side-chain of conjugated oligomer with D-phenylalanine.By mixing Fmoc-L-Phe(9-fluorenylmethyloxycarbonyl-L-phenylalanin)with OTE-D-Phe in a molar ratio of 5:1,a kind of new hydrogel were formed between them through self-assembly.In solution,this hydrogel can spontaneously adsorb bacteria.Furthermore,the hydrogel not only have high bactericidal activity against methicillin-resistant S.aureus(MRSA)and E.coli under irradiation,but also have specific antibacterial activity against MRS A without irradiation.Interestingly,when the hydrogel was put on a piece of cloth by dropwise addition,they also show photodynamic antibacterial activity against MRSA and E.coli as well as specific antibacterial activity against MRSA in dark.In this study,we introduced the"self-assembly" strategy to prepare the hydrogel with a specific antibacterial activity against MRSA.This conjugated oligomer-based hydrogel provides new applications for infected water purification and pathogen therapy.