Optical Properties of Gold Nanorattles: Evidences for Free Movement of the Inside Solid Nanosphere

Gold nanorattles (AuNRTs), hollow gold nanospheres with internal small solid gold nanospheres (AuNSs), were prepared with different sizes. The presence of AuNS inside the hollow gold nanospheres in the nanorattle shape was found to improve their sensing efficiency. The sensitivity factor of the nanorattles is in the range of 450 nm/RIU, while the individual hollow nanosphere’s efficiency is ∼300 nm/RIU. This improvement is due to the strong plasmon field on the cavity and around the inner gold nanosphere as shown by using the discrete dipole approximation (DDA) calculations. Interestingly, this nanoparticle produces a strong enhancement for the interaction of light at 850 nm due to the excitation of both the inner sphere and outer nanoshell, despite being the fact that NIR radiation (850 nm) has very low energy to excite the inner gold nanosphere when present alone. Comparing the experimental and simulated scattering spectrum for a single colloidal nanorattle suggests that the interior gold nanosphere moves freely inside the gold nanoshell. When the rattle is dried, the nanosphere adheres to the inner surface as shown from the experimental and theoretical results. Unlike nanospheres and nanoshells, the nanorattles have three plasmon peaks in addition to a shoulder. This allows the AuNRTs to be useful in applications in the visible and near IR spectral regions.