Linker-Free Synthesis of Core/Satellite Nanoparticles for Single-Particle Surface-Enhanced Raman Spectroscopy and Photocatalysis.

A facile and novel method to synthesize core/satellite (CS) nanoparticles via a linker-free method is reported. Au spheres on the tips of nanostars can gradually grow bigger and eventually transform into gap-enhanced Raman tags (GERTs) to form stable and ultrabright Au nanostar/GERTs CS nanoparticles. Au nanostar/Ag sphere CS nanoparticles can also be prepared via the growth of Ag spheres on the tips, which provides a direct route to new porous Au nanostar/Ag-Au, Ag-Pt, or Ag-Pd sphere CS nanoparticles through galvanic replacement of Ag. In situ surface-enhanced Raman spectroscopy monitoring on CS nanoparticles with different noble metals demonstrates single-particle photocatalysis; among them, the hybrid Ag-Pt CS nanoparticles show the fastest photocatalytic rates for the complete conversion of 4-nitrothiophenol (4-NTP) to 4,4-dimercaptoazobenzene (DMAB) at the single-particle level. This method provides a direct synthetic route to these complex nanoparticles without interference from external linker molecules and opens up new possibilities in single-particle analysis.