The Design Of LCST Ionic Interaction And Its Application For Smart Protection Of Proteins

This thesis includes the following three sections:1. As a particular type of electrostatic interaction, ionic interaction can be used for protection of proteins. However, most of ionic interactions have a character of UCST, which means that the protection existed at room temperature at which proteins work might also restrict activities of proteins. Here we report a novel concept for protein protection via ionic interaction introduced by LCST: the smart protection material interacts with and protects the protein only when temperature rises above LCST, and the protein is released once temperature drops to room temperature. We demonstrate this kind of protection through the interactions between poly (N-isopropyl acrylamide-co-acryloyloxyethyltrimethyl ammonium chloride) (P(NIPAM-co-DAC)) and several proteins including pepsin, urease and HRP. Additionally, interactions of copolymers and charged polystyrene nanoparticles is also introduced and investigated for further demonstration. The LCST ionic interaction induced by thermo-sensitive copolymers realizes the smart protection of proteins, and this concept is novel in existing research.2. With the stabilization of triphenylphosphine, gold nanoparticles (Au-NPs) with a diameter of 2 nm were sythesized by the reduction of sodium borohydride. Then the Au-NPs were modified with PEG-SH and became stable in aqueous solution. Gold nanoclusters were assembled via synthesized pH responsive cross linker and the interaction of PAA&ETC, respectively. The size of obtained gold nanoclusters was well controlled by the PEG-SH molecules modified on each gold nanoparticle. From the result of DLS, the reversible interaction between ETC and PAA which modified on the surface of Au-NPs realized the reversible dissociation of gold nanoclusters. It is known that hydrodynamic diameter < 5.5 nm resulted in rapid and efficient urinary excretion and elimination of quantum dots from the body. So the gold nanoculsters with a character of reversible dissociation have a potential application in drug delivery.3. Polystyrene@silica hybrid microspheres (PS@SiO2) and hollow spheres of SiO2 (HSSi) were prepared using positively charged polystyrene (PS) microspheres as the template. Then, gold nanoparticles (Au-NPs) and silver nanoparticles (Ag-NPs) were modified onto the surface of PS@SiO2 and HSSi respectively through the bridging coupling by mercapto silane coupling agents, which leads to following four kinds of composite microspheres with uniform structures and narrow size distributions:(1) Au-NPs modified HSSi (HSSi-AuNPs); (2) AuNPs modified PS@SiO2 (PS@SiO2-AuNPs); (3) Ag-NPs modified HSSi (HSSi-AgNPs); (4) AgNPs modified PS@SiO2 (PS@SiO2-AgNPs). These composite microspheres were used as SERS substrates, whose sensitivity, reproducibility and stability were evaluated by using crystal violet (CV) as the probe. The detection limits of CV by HSSi-AuNPs, PS@SiO2-AuNPs, HSSi-AgNPs and PS@SiO2-AgNPs are 10-10 mol/L,10-9 mol/L,10-11 mol/L and 10-11 mol/L, respectively. All these substrates exhibit the relatively high sensitivities, and the hollow structures made positive contributions to the sensitivities. Results of repeated Raman measurements of CV on the different spots randomly selected from the substrates confirm that all the substrates have good reproducibility. Moreover, all the substrates have a good stability, because they still have the good sensitivities after having been stored in ambient environment for 3 months.