| Because of the special optical. electrical and magnetic properties and biocompatibility, which make noble metals nanoparticles attractive for a wide range of application on detection, catalysis, bio-sensing, medical imaging and therapy. In recent years, the focus on prepared the gold and silver namoparticles by control of size and shape. According to principles of the preparation, the methods can be divided into physical and chemical methods. The chemical method is a preferable synthetic method due to it is simply and controllable. Further, the chemical methods include aqueous or organic synthesis. The synthesis in aqueous system have attracted great interest because of it is more safe and reliable method. The last century, prepare of gold nanoparticles have been extensively studied as active components. In 1974. Frens prepared various size of gold nanocrystals controlled by the concentration of sodium citrate (Na3Ct). Particular emphasis has recently been placed on the control of shape, because in many cases it allows one to fine tune the properties with a greater versatility than control the size, the anisotropic metal nanocrystals have the potential to applications in biology. Recent studies have emphasized control the shape of nanoparticles Interest in bimetallic Nanoparticles has been growing steadily due to their unique optical, electrical, and catalytic properties. For example, Xia et al. prepared multimetal hollow structures by the galvanic replacement reaction represent, in 2002. It is using silver nanoparticles as the seeds and the mixtures of HAuCl4. In 2003, they control the porous nanoshells with tunable porosities could be conveniently prepared by adding different volumes of HAuCl4 solution to control the dealloying process. They have also prepared multiple-walled nanoshells/nanotubes with a variety of shapes, compositions, and structures by controlling the precursor salt used in each step of the replacement reaction. Chang et al. prepared various Dumbbell-Shaped Au-Ag core-shell nanorods under different pH from silver and ascorbate ions used gold nanorods as the seeds. The morphology of the Au-Ag core-shell nanorods produced depends on the value of pH, due mainly to the value of pH control the concentration of ascorbate ions and the rate of reduction. At every turn, more synthesis utilized Surfactant(CTAB or PVP) as the template to synthesize gold-silver bimetallic Nanoparticles.In our work, Au-Ag bimetallic Nanoparticles were prepared by using gold nanoparticles as the seeds and the mixture of AgNO3 and ascorbic acid as the growth solution, and mixed solution of sodium citrate as agent. By controlling the conditions of reaction to receive high yields, and the SPR of particles is controllable.1,Spend on previous work of gold nanoflowers, and using a special morphology of gold nanoflowers to prepared Au-Ag nanoflowers. Control self-nucleation by changes the ratio of ascorbic acid and silver nitrate. And with increasing the molar ratio of Ag/Au the surface plasmon band of the Ag-Au nanoflowers shifted from 592 to 518 nm, and the resulting bimetallic Ag-Au particles became spherical-like in shape. Surface enhanced Raman scattering (SERS) measurements by using p-mercaptobenzoic acid (p-MBA) indicated that the Au-Ag nanoflowers exhibited improved SERS activity than the gold ones.2,Au-Ag bimetallic Nanoparticles are prepared by 25nm nanoparticles as the seeds. We control the self-nucleation, size and the shape of Au-Ag bimetallic nanoparticles by transfer the value of pH and the ratio of ascorbic acid and silver nitrate. On the basis of that, we mixed solution of HAuCl4 to that one. The purpose is synthesis hollow-shape nanoparticle due to the galvanic replacement reaction, and the Au-Ag-Au hollow-shape nanoparticle is exhibited improved SERS activity for p-mercaptobenzoic acid (p-MBA). In addition, we improved the traditional quantitative method for silver ions, which called Eosin-phenanthroline method. And the method adapt to ascorbic acid as reducing agent... |
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