Tuning of longitudinal surface plasmon resonance peak of gold nanorods for sensor applications

Gold nanorods show interesting optical and electronic properties due to their morphology and are used in different types of sensing applications. For the sensing applications, the dimension of nanorods is very critical and thus the synthesis requires full control over its dimensions. Here we report a novel way to tune the longitudinal surface plasmon resonance peak by fine-tuning the dimensions of gold nanorods. This is achieved by the addition of the gold solution into the final nanorod solution. The color and optical properties of gold nanoparticles originate from the localized surface plasmons and the control of the rod dimensions depend on the double interaction between salt–gold and salt–surfactant (cetyl trimethyl ammonium bromide, CTAB). The different aspect ratio of gold nanorods leads to a huge blue shift from 790 to 557 nm of the longitudinal absorption peak. We propose a particle growth mechanism to change the shape of nanorods to a sphere, which has established applications in various demands, especially in sensing.