Au-Ag core-shell

Fig. 6.8 TEM image of sonochemically co-reduced Au-Ag core-shell bimetallic nanoparticles [37]...

Figure 11.56 Left, Sdiematic illustration of the growth pathways for the Au Ag core-shell nanostructures. Right, representative TEM images of Au Ag core-shell nanoprisms with a gold frism core. The scale bar is the same for all images. Reproduced with permission from reference [131]. (2007) Wiley-VCH Verlag GmbH Co. KGaA.

Tsuji, M., Miyamae, N., Lim, S., Kimura, K., Zhang, X., Hikino, S. and Nishio, M. (2006). Crystal structures and growth mechanisms of Au Ag core-shell nanoparticles prepared by the microwave-polyol method. Cryst. Growth Des. 6 1801-1807. 

Ji X, Xu S, Wang L et al (2005) Immunoassay using the probe-labeled Au/Ag core-shell nanoparticles based on surface-enhanced Raman scattering. Colloid Surf A Physicochem Eng Aspects 257-258 171-175... 

This conclusion would seem to be supported by Hodak et al. [56] who investigated interdiffusion in Au/Ag core/shell nanoparticles. The diffusion constant for the Au/Ag system is given by... 

Figure 7.15 TEM images of Au-Ag core-shell nanorods prepared by the reduction of AgCl on the surface of An nanorods, (a) AucoreAgsheii(thin) nanorods, (b) AucoieAgsheii(thick) nanorods. (Reprinted with permission from C. S. Ah et al. J. Phys. Chem. B 2001, 105, 7871. Copyright (2001) American Chemical Society.)...

Chung E, Gao R, Ko J, Choi N, Lim DW, Lee EK, Chang SI, Choo J (2013) Trace analysis of mercury (II) ions using aptamer-modified Au/Ag core-shell nanoparticles and SERS spectroscopy in a microdroplet channel. Lab Chip 13 260-266... 

Some work has also been recently carried out on the solution synthesis of bimetallic nanorods, employing gold nanorods as preformed cores. Jang and co-workers synthesized Au Ag core-shell nanorods using the electrochemical method to obtain the gold nanorods and the seed-mediated mechanism to get the desired core-shell structure. The combination of the different optical resonances from the core and the shell metals leads to a quite spectacular optical spectrum from these composite, anisotropic nanoparticles. 

Liu, M., and Guyot-Sionnest, P. [2004] Synthesis and optical characterization of Au/Ag core/shell nanorods,/ Phys. Chem. B, 108,5882-5888. Kreibig, U. [1974] Electronic properties of small silver particles the optical constants and their temperature dependence, J. Phys. F Met Phys., 4, 999-1014. 

In order to basically interpret the aforementioned seed-promoted core-shell NC growth mechanism, Tsuji et al. examined the two-step synthesis of Au-Ag core-shell nanostructures [207, 253]. Based on the fact that Au and Ag show the same fee crystal structure with similar lattice constants, nanostructures exhibiting comparable shapes and sizes are expected to evolve. Furthermore Au-Ag core-shell S5 ems are ideal candidates to be investigated at TEM structural analyses as they own different mass contrast therefore easily distinguishable in TEM images [33,253]. 

The enhancement in SERS also depends on the aggregation number of nanostructures, as it exhibits a strong correlation with the number of hot spots in the chains of NPs. ° This effect has been demonstrated for ensembles of monodisperse Au Ag core-shell NPs. ° The NPs were coated with a mono-layer of 2-naphthalenethiol (a SERS analyte), self-assembled and engulfed with a polymer shell (Figure 20). The dimers and trimers with a precisely controlled distance between the NPs were each isolated by differential centrifugation. The ensemble-averaged SERS intensity ratios with respect to... 

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