Modulation of optical properties of gold nanorods on addition of KOH

Gold nanorods are known to exhibit two distinct surface plasmon oscillations namely, transverse and longitudinal bands corresponding to oscillations of conduction electrons along width and length of gold nanorods. Considerable changes in these surface plasmon resonance peak positions occurred when KOH was added to the nanorod solution. Nanorods with initial longitudinal plasmon band at 739, 796, and 895 nm are studied with variation in KOH concentration. While the longitudinal plasmon resonance peak showed blue shift, transverse plasmon resonance peak exhibited only intensity variations. Changes could be attributed to the shape transition of gold nanorods on variation of pH in the solution. Shape transition of gold nanorods is confirmed by transmission electron microscopy images.