One-phase synthesis of surface modified gold nanoparticles and generation of SERS substrate by seed growth method

In this study, we report a novel and facile single-phase synthesis of stable AuNP-CTAB(NA) conjugates with good dispersibility, bearing a bilayer of cationic surfactant, cetyltrimethylammonium bromide (CTAB) supported by N-nonylamine (NA) as a cosurfactant. We investigated AuNP-CTAB(NA) conjugates by (1)H NMR spectroscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and transmission electron microscopy (TEM). These studies suggest the presence of a CTAB bilayer on the nanoparticles surface forming an admicelle and NA embedded in the hydrophobic core of that bilayer. AuNP-CTAB(NA) conjugates remain dispersed in water even in the presence of high concentrations of salt and over a wide range of solution pHs. These conjugates further grow bigger when treated with additional AuCl(4)(-), CTAB, and NA in the presence of the mild reducing agent, hydroquinone (HQ). The larger AuNP-CTAB(NA)-1 conjugates serve as SERS (surface-enhanced Raman Scattering) substrate of Raman active dye even at nanomolar concentrations.