Permeability Control Of Stimuli-Responsive Polymersomes And Design/Applications Of Novel Fluorescent Probes

Stimuli-responsive polymers take adavantage of both the designability, functionability, and topological diversity, et al. advantage of traditional polymers and the specific sensing capability to environmental stimulus of responsive functional group, which have promoted the fast development and the more importance in the fields of fundamental theoretical research, smart metarials, and life bioscience, et al. Among then, in the field of supramolecular self-assembly in especially in the case of using amphiphilic block copolymers, various kinds of artificial nanostructures had been fabricated, like micelles, rod-like micelles, vesicles, large compound vesicles and reverse micelles, et al. Among then, vesicles nanostructures are the most important one due to their unique cell membrane mimetic structure, which so far have been widely used in smart biomimic materials, drug delivery carrier, nano-(micro-) reactor, and even artificial cell (organelle). On the other hand, fluorometric offer distinct advantages in terms of sensitivity, selectivity, fast response, and enhanced spatial and temporal resolution. In recent years, many kinds of fluorescent probe methods have been explored for high efficient and sensitive detection of physical signals, chemical analytes, bioactive molecules, and process of cell metabolism, et al. In the first half part of the current thesis, we explored the vesicular supramolecular self-assembly of stimuli-responsive polymer and the polymersomes nanostructure and property control. In the last half part, the application of the novel fluorescent mechanism of aggreagation induced emission in the field of new type of fluorescent probes have been explored. The first chapter give the brief introduction of the recent development and challenge of the stimuli-responsive polymer in the field of supramolecular self-assembly, and the recent researches and application prospect of the fluorescent probes. In the second chapter, a new kind of photoresponsive polymer has been designed and synthesized, and the corresponding polymersomes bilayer’ permeability change during the photo irradiation process. The third chapter, novel photochromic amphiphilic polymer and the corresponding polymersomes have been designed and fabricated, and the process of reversible polymersomes permeability control upon wavelength selected photo irradiation has been studied. The forth chapter, we integrated the concept of aggregation-induced emission (AIE) with the specific supramolecular recognition between K+ions and crown ether moieties to develop more effective fluorometric K+ probes. In the last chapter, a fluorescent probe system based on enzymetic coupling reaction induced aggregation and emission enhance has been designed, and explored the application in the field of hydrogen peroxide, glucose, and antibody/antigen detection. The dissertation can be further clarified in the following four parts:1. The fabrication of polymersomes exhibiting synchronized covalent crosslinking and bilayer permeabiliza-tion remains a considerable challenge. Presumably, the design of such an optimized polymersome system requires unique crosslinking chemistries and extensive functional group trans-formation during crosslinking. Here we demonstrate a new strategy to solve this dilemma by employing a light-regulated"traceless" crosslinking strategy (Scheme 2-1). In brief, we designed amphiphilic BCPs with the hydrophobic block containing photolabile carbamate-caged primary amine moi-eties. Upon self-assembling into polymersomes, UV-triggered self-immolative decaging releases primary amine moieties, prominent amidation reactions then occur and this leads to prominent vesicle crosslinking instead of vesicle-to-unimer transition, which we initially expected to occur. Most importantly, the crosslinking process is associated with bilayer hydrophobicity-to-hydrophilicity transition. We further dem-onstrate light-tunable co-release of both hydrophilic and hydrophobic molecules encapsulated within polymersomes and light-switchable enzymatic biocatalysis.2. We report on the fabrication of photochromic polymersomes exhibiting photoswitchable and reversible bilayer permeability from newly designed polyethylene oxide)-b-PSPA (PEO-b-PSPA) diblock copolymers, where SPA is a spiropyran (SP)-based monomer containing a unique carbamate linkage. Upon self-assembling into polymersomes, SP moieties within vesicle bilayers undergo reversible photo-triggered isomerization between hydrophobic spiropyran (SP, λ2>450 nm irradiation) and zwitterionic merocyanine (MC, λ1<420 nm irradiation) states. For both SP and MC poly-mersomes, their microstructures are stabilized by multiple cooperative noncovalent interactions including hydrophobic, hydrogen bonding, π-π stacking, and paired electrostatic (zwitterionic) interactions, with the latter two types being exclusive for MC polymersomes. Control exper-iments using analogous block copolymers of hydrophobic SP monomer with a carbonate linkage (SPO) and conventional spiropyran methac-rylate monomer (SPMA) containing a single ester functionality were then conducted, revealing that carbamate-incurred hydrogen bonding interactions in PEO-b-PSPA are crucial for polymersome stabilization in the zwitterionic MC state. Moreover, reversible photo-triggered SP-to-MC polymersome transition is accompanied with membrane polarity and permeability switching from being non-impermeable to selectively permeable towards non-charged, charged, and zwitterionic small molecule species below critical molar masses (e.g., model anticancer drug 2’-deoxy-5-fluorouridine,5-dFu; amino acids). Intriguingly, UV-actuated MC polymersomes possess two types of release modules:1) sustained release upon short UV irradiation duration by taking advantage of the unexpectedly slow spontaneous MC-to-SP transition kinetics (t1/2>20 h) under dark conditions; 2) programmed, on-demand, and switchable release under alternate UV/Vis light irradiation. We demonstrate pho-toswitchable spatiotemporal release of 4’,6-diamidino-2-phenylindole (DAPI, positively charged cell nuclei-staining dye) within living HeLa cells. Reversible light-actuated SP-to-MC transition also rendered facile capture/release of cysteine-functionalized Au NPs at the periphery of MC/SP polymersomes. To further demonstrate the generality and validity of photo-regulated reversible membrane permeability, controlled transport of external amino acids and hydrated protons into fluorescent probe-encapsulated PEO-b-PSPA microcapsule reactors and external stimuli-switchable fluorogenic reactions were successfully achieved.3. In this work, we integrated the concept of aggregation-induced emission (AIE) with the specific supramolecular recognition between K+ ions and crown ether moieties to develop more effective fluorometric K+ probes. We synthesized a novel crown ether-functionalized tetraphenylethene (TPE) derivative, TPE-(B15C5)4, via the thiol-ene click reaction of thiol-derivatized TPE, TPE-(SH) 4, with maleimide-functionalized benzo-15-crown-5 (B15C5). In TPE-(B15C5)4, the TPE core and four outer B15C5 moieties serve as the AIE-active motif and supramolecular K+-recognizing functionalities, respectively. TPE-(B15C5)4 molecularly dissolves in THF with negligible fluorescence emission. As we have envisaged, upon K+ addition, TPE-(B15C5)4 can be effectively induced to aggregate due to K+-mediated cross-linking via the formation of K+/B15C5 (1/2 molar ratio) molecular recognition complex in a sandwiched manner. This process is concomitantly accompanied with the turn-on of fluorescence emission via the AIE mechanism. Thus, TPE-(B15C5)4 can serve as highly sensitive and selective fluorometric off-on K+ probes.4. The development of a highly selective and fast responsive fl uorogenic biosensor for diverse analytes ranging from bioactive small molecules to speci fic antigens is highly desirable but remains a considerable challenge. We herein prop ose a new approach by integrating substrate-selective enzymatic reactions with fl uorogens exhibiting aggregation-induced emission feature. Tyrosine-functionalized tetraphenylethene, TPE-Tyr, molecularly dissolves in aqueous media with negligible fluorescence emission; upon addition of horseradish peroxidase (HRP) and H2O2, effective cross-linking occurs due to HRP-catalyzed oxidative coupling of tyrosine moieties in TPE-Tyr. This leads to fl uorescence emission turn-on and fast detection of H2O2 with high sensitivity and selectivity. As a validation of the new strategy’s generality, we further configure it into the biosensor design for glucose through cascade enzymatic reactions and for pathologically relevant antigens (e.g., human c arcino embryonic antige n) by combining with the ELISA kit.