Green synthesis and formation mechanism of Ag nanoflowers using l-cysteine and the assessment of Ag nanoflowers as SERS substrates

The synthesis and applications of anisotropic nanostructures have attracted much attention in modern nanotechnology. In this paper, based on our previous finding for the synthesis of well-defined and strikingly monomorphic Ag nanoflowers using l-cysteine (l-cys) molecules as both reducing agents and stabilizers, we further investigated the growth mechanism of the detailed structures of Ag nanoflowers. The formation process of the nanoflowers was studied by SEM and UV–vis spectroscopy, showing that there were three key stages in the growth of the Ag nanoflowers: 1) primary nanocrystals agglomerated to form multipod-like nanoparticles 2) the multipod-like nanoparticles aggregated into loose flower-like nanoparticles and 3) the nanoparticles ultimately grew into compact Ag nanoflowers through Ostwald ripening. The growth of Ag nanoflowers is highly sensitive to both the concentration of stabilizer and precursor. Moreover, their potential which is used as a surface enhanced Raman scattering (SERS) substrate was also investigated. The results demonstrate that the Ag nanoflowers exhibit excellent SERS enhancement ability relative to spherical nanoparticles.