Single-particle study: effects of oxygen plasma treatment on structural and spectral changes of anisotropic gold nanorods.

Oxygen plasma treatment is a common method for removing the surfactant capping material from gold nanoparticles, improving their functionalization and lowering their cytotoxicity for biological studies. This single-particle study investigates the effects of oxygen plasma treatment on the structural and localized surface plasmon resonance (LSPR) spectral variations of anisotropic gold nanorods (AuNRs). Single AuNRs subjected to different plasma treatment times were characterized by scanning electron microscopy and dark-field microscopy. The AuNR length was a gradually decreasing function of plasma treatment time. After 120 s of plasma treatment, the aspect ratio of the AuNRs was reduced by a major structural deformation. Furthermore, increasing the plasma treatment time gradually broadened the LSPR linewidth of the single AuNRs. This trend was attributed to the decreased aspect ratio and the increased plasmon damping. These results provide vital and fundamental information on the relationship among plasma treatment time, structural change, and LSPR damping at the single-particle level.