Preparation And Application Research Of Charge Reversible Gold Nanoparticles

Extraction of DNA is a routine work in biological and medical researches and applications. Salt concentration dependent absorption and desorption of DNA on silica particle surface is the mostly used method for extraction of DNA. In such method, usually the efficiency for desorption of DNA under low salt concentration is reasonable since both silica and DNA are negatively charged. However, the efficiency for absorption of DNA is low even under high salt concentration due to weak character of the salt bridge responsible for the absorption of DNA. Modification of silica with amine groups has been proven to be an effective way to increase the absorption efficiency of DNA by direct electrostatic interaction, especially when the amine groups are protonated. However, the desorption of DNA is limited since there is no enough electrostatic repulsion between the silica and DNA even upon the deprotonation of the amine groups. To realize the high efficient extraction of DNA, it is necessary to develop a new method which can allow both high efficient absorption and desorption of DNA. We demonstrated that particles with reversible surface charges is qualified for both high efficient absorption and desorption of DNA. Au nanoparticles were chosen as the model particles due to their feasibility of surface modification. The main content of the thesis as following:1) To fabricate the charge reversible surface, Au nanoparticles were co-modified with thiol ligands terminated with amine and carboxyl groups. The surface charge of the particles was switchable between positive and negative by pH and the isoelectric point (IEP) of the particles was dependent on the ratios of the amine and carboxyl groups on the particle surface. At pH lower than the IEP, DNA could be absorbed effectively on the particle surface via direct electrostatic interaction, which was less sensitive to salt concentration. At pH higher than the IEP, the absorbed DNA could be desorbed almost completely driven by the electrostatic repulsion between DNA and the particle surface. A high DNA extraction efficiency of95%can be achieved by tuning surface charges of the particles with RN/c ratios of0.8according to their IEP.2) In order to avoid the inadequacies of the co-modified gold nanoparticles, such as surface uncompletely replacement, difficulty in precise quantification and so on, we modified gold nanoparticles with bovine serum albumin (BSA). There were seventeen S-S bonds and one thiol ligand on the BSA nolecule. The BSA-modified gold nanoparticles had the same IEP with the BSA molecule at pH4.8. At pH lower than4.8, the nanoparticles carried positive charge, so DNA could be absorbed effectively on the particle surface via direct electrostatic interaction. At pH higher than4.8, the nanoparticles carried negative charge, so the absorbed DNA could be desorbed driven by the electrostatic repulsion between DNA and the particle surface. The absolute adsorption of DNA on the BSA modified Au namoparticles achieved1.8mg/mg, which was much higher than the amine carboxyl co-modified gold nanoparticles.