Highly sensitive and reliable SERS probes based on nanogap control of a Au-Ag alloy on silica nanoparticles

We developed highly sensitive surface-enhanced Raman scattering (SERS) probes based on SiO2@Au@Ag nanoparticles (NPs) using the Ag growth onto Au NP seeds method. The SiO2@Au@Ag NPs were synthesized by reducing Ag ions under mild conditions (ascorbic acid) and using the structure-directing agent polyvinylpyrrolidone (PVP). SERS activities of the NPs were tuned by adjusting AgNO3 concentration, resulting in the growth of the Ag shell on the surface of the Au NP seeds and the formation of narrow gaps between two Ag NPs on the surface of the probes. The NPs exhibited strong Raman signals originating from a highly enhanced E-field at the gaps. The SiO2@Au@Ag NPs exhibited a low limit of detection (LOD) value of 2.4 nM for ATP, which proves that they are highly sensitive probes. Moreover, reproducible Raman signals of the SiO2@Au@ Ag NPs toward ATP were obtained in batch-to-batch experiments which is very promising for potential use in on-site detection.