Galvanic Replacement-Free Deposition of Au on Ag for Core–Shell Nanocubes with Enhanced Chemical Stability and SERS Activity

Abstract

We report a robust synthesis of Ag@Au core-shell nanocubes by directly depositing Au atoms on the surfaces of Ag nanocubes as conformal, ultrathin shells. Our success relies on the introduction of a strong reducing agent to compete with and thereby block the galvanic replacement between Ag and HAuCl4. An ultrathin Au shell of 0.6 nm thick was able to protect the Ag in the core in an oxidative environment. Significantly, the core-shell nanocubes exhibited surface plasmonic properties essentially identical to those of the original Ag nanocubes, while the SERS activity showed a 5.4-fold further enhancement owing to an improvement in chemical enhancement. The combination of excellent SERS activity and chemical stability may enable a variety of new applications.

Ag Nanoparticles Decorated Cactus-Like Ag Dendrites/Si Nanoneedles as Highly Efficient 3D Surface-Enhanced Raman Scattering Substrates toward Sensitive Sensing

“…5,6 However, the biggest obstacle to the expansion of the scope of practical application for SERS sensing is the lack of highly efficient substrates with uniform and high-density hotspots. [7][8][9] Recently, extensive efforts have been devoted to construct different SERS substrates from zerodimensional clusters (Au or Ag nanospheres, 10,11 nanocubes 12,13 ) to 3D hierarchical nanoscaffolds (nanoarrays, 14,15 branched nanotrees, 16,17 nanobutterfly wing 18,19 ). Notably, 3D nanostructures are far superior owing to their potential for the arrangement of hotspots along the third dimension.…”

Local Plasmonic Studies on Individual Core–Shell Gold–Silver and Pure Gold Nano-Bipyramids

“…Furthermore, extra resonances and new modes have been reported to depend on the silver content, as some of them are directly associated with silver SPR, 15,40,41 others to the shape of the object 12,42 and even to the arrangement/assembly of these nanostruc tures. 40,43,44 These results demonstrate the interest in bimetallic materials. However, detailed local analyses are needed to disentangle the effect of the core−shell structure and of other structural parameters on the optical properties of these materials.…”

Dynamic Chiral Nanoparticle Assemblies and Specific Chiroplasmonic Analysis of Cancer Cells

“…[ 11 ] Fortunately, galvanic replacement was successfully suppressed by controlling the pH at 9.5. [ 12 ] This was because the HAuCl 4 solution could be alternatively reduced to generate a conformal Au shell on the Ag NPs ( Figure S2, Supporting Information). The elemental mapping in Figure 2 A,B depicts the Ag-core/Au-shell structures for Ag@Au 1 NPs and the AuAg-alloy frameworks for Ag@Au 2 NPs.…”

“…[ 18,19 ] The best plasmonic electronic oscillations of the Ag core and the high electron affi nity of the Au shell strengthen the interaction of the hybrid electronic waves of the Ag and Au, and also accelerate the "hot" electron transfer, resulting in an enhancement of the electromagnetic fi eld and the hybrid coupling between the Ag core and the Au shell; [ 10,20 ] iii) Au is signifi cantly less polarizable, which implies that dispersion interactions will be less important for Au. [ 19,21 ] The Au shell could not only effectively protect the Ag core to preserve its LSPR properties in an oxidative environment, but also presents a better chemical stability than the pure Ag NPs, thus improving the reliability of chiral signal; [ 10,12 ] iv) The deposition of the Au shell on the Ag NPs increases their size and strengthens the asymmetric structures of the Ag@Au 1 NP assemblies, which plays an extraordinary critical role in the intensifi cation of the asymmetrical dipoledipole coupling and the inversion of the chiral geometry. [ 4c , 7a ] To gain more insight into the coupling interactions of the Agcore/Au-shell behind the observed chiro-optical response, we also collected the CD response of hollow Ag-core/AuAg-alloyshell NP assemblies.…”