Large-Area Monolayer Films of Hexagonal Close-Packed Au@Ag Nanoparticles as Substrates for SERS-Based Quantitative Determination.

In this work, quasi-spherical, small-sized, citrate-stabilized, core-shell (CS)-structured Au 5.5 @Ag m nanoparticles (NPs) with Ag shells of controlled thicknesses ( m = 0, 1.25, 3.25, and 5.25) were successfully synthesized by using Au NPs with sizes of 5.5 nm as seeds. The as-prepared Au@Ag NPs after the phase transfer process were further used for the fabrication of high-quality large-area monolayer films of hexagonal close-packed Au@Ag nanoparticles (LAMF-HCP-Au@Ag NPs) by our improved self-assembly at the interface of toluene-DEG containing a proper amount of water (10% v/v). Moreover, after transferring the as-prepared LAMF-HCP-Au@Ag NPs onto polydimethylsiloxane (PDMS) substrates (LAMF-HCP-Au@Ag NP@PDMS substrates), the resulting LAMF-HCP-Au@Ag NP@PDMS substrates can exhibit uniformity in the intensity of the surface-enhanced Raman scattering signals. Furthermore, taking LAMF-HCP-Au 5.5 @Ag 5.25 NP@PDMS substrates as an example, they can achieve quantitative detection with high sensitivity for crystal violet (CV) and 4-aminothiophenol (4-ATP) in the range from 10 -12 to 10 -7 M and from 10 -13 to 10 -7 M, respectively. Also, their limit of detection (LOD) for CV and 4-ATP are 10 -12 and 10 -13 M, respectively. Especially, the LOD for CV can also be as low as 10 -13 M by extending the immersing time.