The Research On The Modification Of Au Nanoparticles And Its Responsive Behavior

Biological detection is one of the most important application fields for nanoparticles. To obtain nanomaterials, biomolecules are often used to modify the nanoparticles. In Biological system, many bioactive molecules, such as metabolized molecules, amino acid and peptides and so on, are all have the ability of special response to stimuli, and then modulate the function of the organism which secured the maintaining of the living. That makes us further understand the preparation of nanomaterials. At the same time, the researches on the biological detection and molecule identifying behavior get more developing opportunities.In this paper, we modified Au nanoparticles with citrate, histidine and poly-histidine respectively and did research on their responsive behaviors to outer stimili such as metal ions, pH value and temperature. We monitored the identification process of the biological ligand on the surface of the nanoparticles.The whole dissertation includes four parts:1. We demonstrated that the citrate capped Au nanoparticles present pH-dependent response to Pb2+ ions. At pH of 11.2, other heavy metal ions with strong affinity to the carboxyl group become less effective to induce the color change of the Au nanoparticles because of the competition effect of hydroxyl groups. However, the Au nanoparticles are still sensitive to Pb2+ ion at pH of 11.2 due to its amphoteric character. The citrate capped Au nanoparticles show selective response to Pb2+ ions as a result of suppressed coordination of other interfered heavy metal ions with the carboxyl groups at pH of 11.2.2. And the citrate-capped Au nanoparticles can undergo Cu2+ ion induced pH-dependent aggregation due to the competition effect of hydroxyl groups with the carboxyl groups. At pH = 8.9, the aggregation process is identified to be dominated by the cluster-cluster mechanism if the coordination interaction can facilitate the cross-linking of the particles. At the high pH value (10.1), the coordination of Cu2+ ions with the carboxyl groups is suppressed by the competition effect of hydroxyl groups, thus the inter-particle interactions are weakened and the aggregation process follows the particle-cluster mechanism. It is proposed that the introduction of ligands with different affinity to metal ions will be helpful for the construction of aggregates of nanoparticles with desired structures and functions and the improvement of the selectivity and sensitivity in the colorimetric detection of heavy metal ions by using nanoparticles.3. We study the pH-dependent aggregation of the histidine-functionalized Au nanoparticles induced by Fe3+. Histidine is anchored to the Au nanoparticle surface via its carboxyl group and N1- of imidazole. At low pH value, histidine acts as a monodentate ligand, and Fe3+ is expected to coordinate with N3- sites of histidine ligands from neighboring particle surfaces, which induces aggregation of Au nanoparticles. At high pH value, histidine is transformed into a bidentate ligand after the deprotonization of its R-NH2, and thus the aggregation process is suppressed greatly. The pH-dependent aggregation of histidine-functionalized Au nanoparticles is identified to show pretty good selectivity to the Fe3+ ion.4. We demonstrated that the aggregation of the Au nanoparticles functionalized by PLH can be switched by the dual-stimuli of pH and temperature. It is identified that the aggregation of the particles is related to the conformation changes of PLH loaded on the particle surface. The dual-stimuli, pH and temperature, must act in a cooperative way to switch the hydrophobic β–sheet structure PLH and thus trigger the assembly/disassembly of the Au nanoparticles. The aggregation process and thus the conformation changes of PLH can be well recognized by the color change of the Au nanoparticles by naked eyes. Such a cooperative dual-stimuli triggered assembly/disassembly process of the Au nanoparticles may afford new chance to develop simple colorimetric method for investigating the structures and properties of polypeptides and devise smart nanostructures with potential applications in biosensors and bio-labeling.