Synthesis, Functionalization And Applications Of Stimuli-Responsive Nanoparticles

Nanotechnology and intelligent materials have continually been one of the most attractive research topics in recent years. As one of intelligent materials, stimuli-responsive nanoparticles have been widely used in the field of catalysis, bio-imaging and drug delivery because they combine the advantages of nanoparticles with their stimuli-responsive properties. The stimuli-responsive properties can be altered or enhanced by the functionalizations of nanoparticles or their precursors, which may highly improve their applications in different areas. In this thesis, several kinds of representative nanoparticles have been synthesized, including spherical polyelectrolyte brushes (SPB), amphiphilic random copolymer and dendrimer, to study their stimuli-responses and applications.1. Hybrid emulsion polymerization was used to encapsulate quantum dots (QDs) into the core of polystyrene (PS), polyacrylic acid (PAA) chains were then grafted onto the surface of PS core to form anionic fluorescent spherical polyelectrolyte brushes. Transmission electron microscope (TEM) results indicated that QDs formed clusters in the presence of surfactant and sonication, and then confined inside the core of PS. The contents of QDs inside the PS core could be adjusted by changing the feed ratio of QDs and styrene monomer. When AA monomer was used for grafting, the chain length decreased along with the increase of QDs contents. The fluorescent SPB combines the fluorescent properties and the conventional stimuli-responsive properties. The fluorescence intensity can be adjusted by altering the contents of grafted PAA chains.2. Polyvinyl carbazole (PVK) nanoparticles with narrow size distribution was prepared by conventional emulsion polymerization using vinyl carbazole (VCz) as monomer. PAA chains were then grafted onto PVK core by photo-emulsion polymerization to form PVK SPB. DLS results showed that the average diameter of PVK core is 175 nm, and the chain length is about 230 nm. The synthesized PVK SPB is also stimuli responsive. In the range of experimental conditions, the hydrodynamic diameter of which increased along with the increase of pH, while it reduced with the increase of the concentration of silver nitrate (AgNO3). Since counterion Ag+could be adsorbed by SPB and confined in the shell, sodium borohydride (NaBH4) was used to reduce Ag+ to prepared well-distributed silver nanoparticles using PVK SPB as carrier. The loading content of silver nanoparticles was highly enhanced by repeat loading. Finally, layer-by-layer self-assembly was used to construct anti-bacterial film with high silver content using silver loaded PVK SPB as precursor, which showed high anti-bacterial performance.3. Pyridyl disulfide ethyl methacrylates (PDSMA) monomer was synthesized, and amphiphilic random copolymer PDS-PEG was prepared by RAFT polymerization. Then Post-polymerization modifications were applied to introduce o-nitrobenzyl, ketal or benzsulfamide groups to separately the polymer backbone by thiol-disulfide exchange, and three different dual stimuli-responsive polymers were obtained. In addition, o-nitrobenzyl and benzsulfamide were concurrently introduced to construct a multi-stimuli responsive polymer. All these polymers can form stable micelles in water, encapsulate hydrophobic guest molecules, and show responsive properties to corresponding stimuli. For example, after the introduction of o-nitrobenzyl group, when the polymer is in the presence of a high concentration of glutathione (GSH), the disulfide linkage is reduced to free thiol. Since the hydrophobicity of thiol is much lower than o-nitrobenzyl, which leads to the disruption of hydrophilic-hydrophobic balance. As a result, the guest molecule is released. While upon UV irradiation, the o-nitrobenzyl group is cleaved from polymer backbone with the following generation of a by-product 2-nitrosobenzaldehyde, which also leads to the disruption of hydrophilic-hydrophobic balance and the release of guest molecules. Other three polymers are responsive to pH/redox, specific protein/redox and light/specific protein/redox, respectively. This method allows the simplicity and flexibility of synthesis and purification of dual/multi-stimuli responsive nanoparticles with no effect on polydispersity, thus exhibiting more flexibility and applicability to polymer functionalization.4. A AND logic gated dendritic system has been synthesized. The dendrimer was constructed from a biaryl monomer, in which two repeating units contain both hydrophilic PEG moieties and hydrophobic alkyl chains; one repeating unit contains alkyl chain and triple bond as functional group. A PEG derivative containing azido and o-nitrobenzyl masked benzenesolfonamide at one end was synthesized, which was further conjugated to dendrimetic scaffold via click chemistry. Since the benzsulfamide is masked by nitrobenzyl group, which hinders the protein-ligand interactions between carbonic anhydrase (CA) and sulfonamide. Therefore, CA as a single input would not induce disassembly. When UV light is applied as a single input, nitrobenzyl group is cleaved from the ligand. Since the ratio of the ligand is low and the hydrophilicity before/after cleavage is close, there would be no obvious effect on the hydrophilic-lipophilic change to cause disassembly. Upon UV irradiation, benzsulfamide ligand is generated from this system. CA as another input is able to subsequently bind to the amphiphile, leading to protein-binding induced disassembly and non-covalent guest release. This AND logic disassembly and non-convalent release could potentially increase the drug delivery specificity on protein disorder treatments.