In summary, we successfully developed a simple one-step synthesis of a plasmonic colloidal gold nanowire with broadband absorption in the visible and near-infrared ranges. The growth mechanism was driven by the assembly and the fusion of small in-situ formed spherical particles (~5 nm). The gold particles displayed strong NIR photothermal as well as SERS performance. The SERS properties of the particles enabled us tomonitor the plasmon-induced crosslinkingof designed thiolated diazonium compoundsadsorbed on the gold surfacevia Au-S bond. The SERS spectra indicate the self-assembly of the molecules onto the gold surface in a dimer form via N=N coupling, while continous irradiation led to crosslinking of the molecules and discossiation of N2.