Morphology Control, Self-assembly And Surface Enhance Raman Scattering Of Gold Nanoparticles

It is of great value to expand the application of gold nanoparticles in biology,sensing and medicines by controlling the morphology and monodispersity. Therefore,the study reported a seed-mediate synthesis of decahedron gold nanoparticles withPoly (vinyl pyrrolidone)(PVP) act as a capping agent and Dimethyl Formamide (DMF)as a reducing agent. Also, truncated decahedron, five-pointed star decahedron,pentagon decahedron (PD) can be synthesized by decreasing the concentration of goldprecursor (HAuCl4). In the twin crystal system, the synthesis achieved the transitionsfrom decahedron to PD which composed of low energy {111} facets and high energy{110} facets respectively. At the same time, the octahedron gold nanoparticles havebeen synthesized by a seed-mediate method, truncated octahedron Ⅰ,truncatedoctahedronⅡ,rhombic dodecahedron (RD) can be synthesized via decreasing theconcentration of the seed4. The synthesis method can guarantee the morphologyevolution of single crystal from octahedron to RD, which surrounded by low energy{111} facets and high energy {110} facets respectively. In general, to realize theconversion from low energy {111} facets to high energy {110} facets either in twincrystal or single crystal system, it is of great importance to control the twinned andsingle nanocrystal seed in the initial nucleation process of PVP+DMF system.In addition, the research investigated the optimal synthesis condition and growthmechanism of icosahedron twin gold nanoparticles that consist of twenty {111} facetswith PVP and DMF by one-step synthesis without seed nanocrystal. To detect theeffect of DMF served as a reducing agent, the500nm RD gold nanoparticles were produced without any capping agent but just adding gold precursor and DMF.Transition morphology of RD and it’s evolutionary process can be obtained byprolonging the reaction time. If a little amount of ascorbic acid (AA) was introduced inDMF system, the concave RD gold nanoparticles with inconspicuous edges andcorners were formed. The FT-IR characterization has shown that DMF moleculesadsorbed on the gold nanoparticles which may inhibit the growth of {110} facets thatfinally lead to the formation of RD. By means of the evolution morphology analysis,we suggest that crystal growth rates for the gold nanoparticles follow the order of[111]>[100]>[110] in the DMF system under the condition of the lower reactiontemperature.Meanwhile, the study explored the self-assembly of octahedron, RD, PD goldnanoparticles. The self-assembly gold nanoparticles formed long-range face-centeredcubic structure on the silicon substrate spontaneously. The concentration of goldnanoparticles and the Van Der Waals interaction between gold nanoparticles were themajor factors that responsible for the formation of self-assembly structures. To takeadvantage of the Surface Enhanced Raman Scattering (SERS) of the gold nanoparticles,the self-assembly structures have been used to probe the4-aminothiophenol (4-ATP).The results shown that the detectable concentration can be as low as10-6mol/L and theSERS enhancement factor(EF) for RD, PD, Octahedron are0.40×10~7,0.31×10~7,0.29×10~7at minimal. Among all the concentration of4-ATP solution, the RD exhibitsthe most obvious enhancement and strongest EF. The probably SERS mechanism ofgold nanoparticles may be the co-action of Chemical enhancement mechanism andElectromagnetic enhancement mechanism.