From gold nanorods to nanodumbbells: a different way to tailor surface plasmon resonances by a chemical route

Spherical ended and arrow ended gold nanodumbbells were synthesized by a simple approach of introducing gold nanorods to solutions of sodium hydroxide and ascorbic acid, respectively. From UV-visible absorption spectroscopy, the transverse and longitudinal surface plasmon resonance that corresponds to electron oscillations perpendicular and parallel to the gold nanorods showed either blue or red shift, depending on the concentration of the acid or alkali solution. The morphological change from gold nanorods to spherical ended and arrow ended dumbbells was assessed by transmission electron microscopic (TEM) analysis. A theoretical model using the volume integral equation method was used to simulate the surface plasmon resonance of the gold nanodumbbells, which was in good agreement with the experimental observations. From the experimental observations and numerical calculations, a new growth mechanism for gold nanodumbbells is proposed.