Bumpy Hollow Gold Nanospheres for Theranostic Applications: Effect of Surface Morphology on Photothermal Conversion Efficiency

The combination of hollow core and rugose surface morphology is highly attractive for photoactive near-infrared (NIR) nanomaterials. Here, we present a facile pH modification to hollow gold nanosphere (HGN) synthesis to enable controlled tuning of the surface morphology from smooth to very bumpy. Unlike other methods, the synthetic protocol does not require harsh surfactants, secondary reducing agents, or organic solvents. The resultant bumpy HGNs (bHGNs) are highly monodisperse with little variation in protrusion length from particle to particle. Mechanistic studies suggest that surface rugosity is mainly controlled by the presence of free OH– ions in solution. We also present the first systematic investigation into the effect of surface morphology on the photothermal conversion efficiency (PCE) of bumpy as well as smooth HGNs, with a maximum PCE reaching 99%. Although expected to have a higher scattering component, the bHGNs retain the excellent PCE of their smooth counterparts, which may be due to efficient reabsorption of scattered light