Silver nanocrystals with special shapes: controlled synthesis and their surface-enhanced Raman scattering properties

Silver (Ag) nanoparticles with dendritic, urchin-like, flower-like and sphere-like shapes were controllably synthesized in aqueous hydrogen fluoride (HF) solution at room temperature. The shape of the Ag nanoparticles can be tuned from dendritic to urchin-like, flower-like and sphere-like by increasing the concentration of polyvinyl pyrrolidone (PVP, MW = 55 000) from 2 to 11 mM. As-synthesized Ag nanostructures were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The morphology-dependent surface-enhanced Raman scattering (SERS) of the as-synthesized Ag nanostructures was investigated. The results indicated that flower-like Ag nanostructure had higher SERS activity than other Ag nanostructures for 4-mercaptobenzoic acid (4-MBA) probe molecules. Moreover, the resultant substrate can be applied in the label-free detection of DNA with a sensitivity limit as low as 50 nM.