Spectroscopy Characterization Of Nanometer Gold And Lysozyme And Myelin Basic Protein Interactions

Gold nanoparticles (AuNPs) have been extensively studied for a long time due to their chemical stability, biocompatibility and unique optical properties. Interactions between AuNPs and protein were investigated by UV-vis absorption, fluorescence, circular dichroism (CD) and transmission electron microscope (TEM) in this thesis, effects of temperature, salt concentration, pH and membrane mimics on the interaction or aggregation of AuNPs were also investigated.This thesis is consisted of three parts:1. Literature reviewThis part briefly described the interaction between nanoparticles and protein or cell membrane, properties and application of AuNPs, current research method of the interaction between AuNPs and protein, and properties and functions of myelin and myelin basic protein (MBP). Base on these the research programs of this thesis were proposed.2. The interaction between AuNPs and lysozymeThe interaction between AuNPs and lysozyme were characterized by UV-vis absorption, fluorescence, CD and TEM measurements. Experimental results revealed that the surface plasmon resonance band of AuNPs showed an apparent broadening and red shift, and the position of the maximum absorption was shifted from520to540nm, when lysozyme molecules absorbed on the AuNPs surfaces. The analysis of the quenching results has been performed in the terms of the Stern-Volmer equation, from this equation the value of bimolecular quenching rate constant Kq=4.5×1016L·mol-1·s-1was obtained, which suggested that the dominating quenching mechanism was static. the values of the binding constant Kb and binding sites n was2.9×1011L-mol"1and1.3respectively. CD studies suggested the decrease of the a-helix in the lysozyme secondary structure was happened after adding the AuNPs solution. In addition, temperature, pH and the sample introducing order have great effect on the interaction between AuNPs and lysozyme. NaCl with high concentration and cationic surfactant dodecyltrimethylammonium bromide (DTAB) can cause serious aggregation of AuNPs, while lysozyme can obviously inhibit the aggregation. Anionic surfactants sodium dodecyl sulfate (SDS) and dodecyl phosphorylcholine (DPC), neutral surfactants dodecyl-beta-D-malt glycosides (DDM) and Triton X-100have little effect on the stability of AuNPs, but SDS and DPC can reduce the aggregation of AuNPs caused by lysozyme to a certain extent.3.The interaction between AuNPs and myelin basic protein (MBP)UV-Vis absorbance spectrum in combination with fluorescence spectroscopy, CD and TEM were employed to investigate the interaction between MBP and AuNPs. Binding of MBP molecules to AuNPs surface results in the red shift and broaden of the nanoparticle resonance plasmon band. The fluorescence quenching experiments indicated that static quenching occur between MBP and AuNPs. The binding constant Kb and binding sites n of AuNPs to MBP were calculated to be1.7×1010L·mol-1and1.2, respectively, according to the double logarithm regression curve. The CD spectrum indicated that that AuNPs has little effect on the conformation of MBP. pH affect the interaction between AuNPs and MBP greatly. NaCl with high concentration can cause AuNPs to aggreate greatly, while the existence of MBP can reduce such aggregation. In the presence of MBP, DPC and DDM, as membrane mimics, can cause slight increase or decrease of AuNPs aggregation, which depends on the surfactant concentrations employed.