ABSTRACT
We describe a novel protocol for a one-step, seed-less, organic solvent- and surfactant-free synthesis of optically dense aqueous colloids of gold nanoflowers (AuNF), with tunable absorption wavelength between 620 and 800â¯nm. We demonstrate that simple variation of the ratio of two reagents allows the plasmonic band position to be tuned to any desired wavelength⯱â¯5â¯nm, namely to those of the laser sources commonly used for SERS spectroscopy. The AuNF size distribution was sufficiently narrow, comparable to that known with seed-mediated synthesis. The AuNF have been validated as efficient aggregation-free substrates for surface-enhanced Raman scattering (SERS) spectroscopy using two common fluorescent dyes, Nile Blue and Crystal Violet, both thiol-free. Their fluorescence was quenched and SERS signal intensity was a linear function of the dye concentration, from nanomolar to micromolar range. Easy to prepare and to use, these AuNF appear as a particularly user-friendly and efficient way to obtain plasmonic substrates for SERS in the red and deep red spectral range.