Modification And Assembly Of Gold Nanoparticles With Lysine And Lysine Peptide

Most important biomolecules, such as protein, DNA etc, their sizes are 2 to 200 nm similar to nanoparticles. Because of the special structure and fundamental features, biomolecules display several surface and interface properties. Through the modification of nanomaterials that are important for the binding with biomoleculer for the formation of nanoparticle architectures of predesigned shapes, sizes and compositions. Nanoparticles have highly interesting optical, electronic, and magnetic properties due to the quantum confine effects and surface effects. The using of nanoparticles as biotechnological tool is particularly attractive. Peptide or protein, as one of the most important biomolecules, is particularly suitable to serve as a construction material in nanoscience.On the point of physical chemistry and biochemistry, this dissertation is focused on studying the interactions at the interfaces of the lysine, lysine peptide and nanoparticle. It is attempted to supply a new way to nano-assembly or detection of amino acid and peptide.There are mainly four parts in the dissertation:1) The modification of gold nanoparticles with lysine and lysine peptide are studied. It is found that lysine can bond to gold nanoparticles withε-amino group of L-lysine. The longer the lysine peptide length is, the stronger the adsorption ability to gold nanoparticles becomes. Thus, the stability of gold nanoparticles is enhanced for the salt resistibility. This provides a good approach to design the modification of nanoparticles.2) An assembly of Au nanoparticles is fabricated by the condensation of peptide bonds between L-lysine molecules attached to the surface of 13 nm Au nanoparticles. The formation of peptide bonds between the L-lysine molecules is confirmed by Raman spectra. It is found that L-lysine molecules are absorbed onto the Au colloid surface via the interactions between theε-amino group of L-lysine and the Au colloid. UV–visible spectral measurements show there are strong interactions between the Au nanoparticles linked by dipeptides (lysine–lysine) in the self-assembly. Transmission electron microscopy observations show that the distance between the two adjacent nanoparticles is about 1.5 nm, which is consistent with the calculated length of the dipeptide.3) Oligolysines directed one-dimensional assembly of gold nanoparticles is reported. This is similar assembly process by dilysine and trilysine. The linear assembly is induced by partial removal of the citrate stabilization shell, which results in an increase in interparticle electric dipole-dipole interactions. However, tetralysine, pentalysine and hexalysine have not brought out a linear assembly due to the longer peptide can directly combine the gold nanoparticles. So a three-dimensional assembly is induced.4) Poly-L-lysine functionalized gold nanoparticle (PLL-GNP) was found to go reversible assembly/disassembly in the range of pH from 6.5 to 11.0 at room temperature. At high pH value, the deprotoned lysine residues allow the formation ofα-helix andβ-sheet at the expense of a part of random coil andβ-turn, thus inducing the assembly of GNPs. With decreasing the pH to 6.5, the assembly of GNPs is disrupted due to the conversion ofα-helix andβ-sheet back into random coil andβ-turn. It is identified that the formation/collapse of antiparallelβ-sheet structure among PLL chains from adjacent GNPs is responsible for reversible pH-dependent assembly/disassembly of GNPs. Since the conformation induced assembly/disassembly process of the PLL-GNP can be well recognized by shift of the surface plasmon resonance band of GNP and the color change of the solution, this study puts forward the possibility to follow the conformation change of peptide by monitoring the spectral change of GNP. We also demonstrate the construction of a cooperative dual-responsive PLL surface switching between superhydrophilicity and superhydrophobicity. The dual-responsive unfolding/ aggregation of the polypeptide are responsible for reversible switchable wettability of the surface. Such a work may afford a model to understand surface properties of polypeptides and proteins and be helpful for the devise of smart surfaces with potential applications in nanodevices, bioseparation and biosensors.