| Gold nanoparticles is a stable classical nanomaterial, which is focus in the research and application of optics, optoelectronics, catalysis, nanostructure fabrication, and chemical/biochemical sensings due to its special stability and bio-affinity. Soluble gold nanoparticles is very interesting due to their good biocompatibility, wide academic study and application in this field.Up to the present, various methods of water-soluble gold nanoparticles is reported. Simple, low polydispersion and controllable sizes have always been purpose. In many methods, the Frens method have been the classic method of water-soluble gold nanoparticles, which is a HAuCl4-citrate Reduction Method in 1973. In the process, the citrate is not only reducing agent but also a stabilizer, the molar radio of citrate/HAuCl4 can control the size of gold nanoparticles, but the polydispersion increases with the increase of particles and the shape of particles put up elliptical or other irregular shapes and the stability of particles decreases. Particularly, the similarity can hardly control between batches. Though people carried on a few improvements and research to that method, to control the shape and the size and to understanding the process of the gold nanoparticles formation is still worthy of concern of topic.This thesis is totally divided into three parts:Chapter 2, we improve Frens method further on the foundation of above research and synthesize various size gold nanoparticles by changing the molar radio of citrate/HAuCl4, moreover, the polydispersion of gold nanoparticles is limited in 5～10% while the molar radio of citrate/HAuCl4>7.0. And we put forward citrate as a kind of strong alkali weak sour salt can not only be reducing agent and stability but also can regulate the system pH value. The system pH value increases and the OH- of solution replaces the Cl of the HAuCl4 matches to form more stable HAuClx(OH)4-x with the increase of the concentration of citrate gradually, and then the rate of reaction reduces. Furthermore the OH- of solution replaces the Cl of the HAuCl4 matches to form more stable HAuClx(OH)4-x mostly, but the OH- of the citrate molecule of the surface of small particles replaces the Cl of the HAuCl4 matches rarely, so the conglomeration and anisotropy of particles reduces during the process with the pH value increasing; The OH- of the citrate molecule of the surface of small particles replaces the Cl of the HAuCl4 matches to form more stable HAuClx(OH)4-x mostly, so the conglomeration and anisotropy of particles increases during the process with the pH value reducing. Therefore we put forward different nucleation and growth process under the different condition that deepen the understanding of the whole system.Chapter 3,We studied the influence of a pH value to the spheroid Au nanoparticles and synthesized the different sizes and size symmetrical spheroid gold nanoparticles under low ratio of Citra/HAuCl4, but adding NaOH aqua to raise system pH value. Moreover, we maked use of TEM, Uv-vis and DLS to monitor [AuCl4-] and the formation process of the Au nanoparticles, to prove two kinds of growth ways of gold nanoparticle and the control of the pH to the reduction velocity and the reaction kinetics of AuCl4- under the different pH value by different concentration of citrate.Chapter 4, we make use of the adjust and control function of pH value for the growth of particles, the 25 nm gold nanoparticles be a seed, NH2OH be reducing agent, to synthesize the branched gold nanoparticles by adjusting the pH value of the HAuCl4 solution before passing reaction. The OH- of solution replaces the Cl of the HAuCl4 matches to form more stable HAuClx(OH)4 - x that leads the oxidation-deoxidize potential of Au3+ to reduce and the rate of reactivity to slower, and results in forming branched gold nanoparticles. Due to the special optics property of the branched gold nanoparticles, we researched into its surface character primarily through the ion detection.
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