A novel strategy is used to synthesize porous gold-silver alloy nanospheres encased in ultrathin silica shells that can act as highly sensitive single-particle probes.
Gold (Au) and silver (Ag) nanoparticles are typical plasmonic nanoparticles that exhibit an intense electromagnetic field in their proximity when they are irradiated by incident light. Within these fields—known as ‘hotspots’—the Raman scattering of molecules can be magnified by many orders of magnitude (depending on the intensity of the local electric field). In this so-called surface-enhanced Raman scattering (SERS) phenomenon,1 the Raman scattering signals contain information relating to the bond vibrations and thus provide ‘signatures’ of the molecules (which enables their spectroscopic detection). In the pursuit of high-sensitivity SERS analyses, it is therefore highly desirable to specifically construct hotspots.