Bimetallic nanocrystals have received ever-growing interest owing to their properties often superior to the monometallic counterparts. Among various methods, seeded overgrowth has emerged as the most powerful route to the synthesis of core-frame or core-shell bimetallic nanocrystals. However, it simply cannot be applied to two metals with built-in galvanic replacement between them. In the past, we successfully demonstrated the galvanic replacement-free deposition of Au on Ag nanocrystals by introducing an additional reducing agent that can quickly reduce the metal precursor before it undergoes galvanic replacement with the seeds. In this talk, by building upon the prior success, we report our progress to turn the successful synthesis into a model system for investigating the fundamentals involved in the heterogeneous nucleation and overgrowth of metal nanocrystals. We hypothesize that the vibrational frequency of a metal-sensitive molecular probe can serve as a distinctive reporter for the metal being deposited on the surface of a Ag nanocrystal, with a detection limit well below one monolayer. To validate our hypothesis, we develop a novel class of fingerprint probes based on isocyanide compounds (R–NC) for the in-situ characterization of the heterogeneous nucleation and early-stage deposition of a metal, such as Pd, Pt, Ir, Rh, or Ru, on the edges of Ag nanocubes by surface enhanced Raman scattering (SERS). This research will create new foundation for the design and rational synthesis of bi- and multi-metallic nanocrystals sought for a variety of applications.