Plasmon resonances of novel monolayer and bilayer shell aggregate gold nanostructures

摘要

Various gold nanostructures have being investigated for medical and biological uses, such as surface enhanced-Raman spectroscopy (SERS) and photoacoustic imaging (PAI), each having its advantages and limitations depending on the specific application. For many imaging and spectroscopic applications, it would be beneficial to use near infrared (NIR) excitation as well as small gold nanospheres which can easily reach the cytoplasm and cell nucleus. For that purpose, we propose a novel nanostructure, the "shell aggregate," which consists of small nanospheres aggregated (mono/bi-layer) around a core such as an intracellular organelle. The extinction efficiency of such monolayer and bilayer shell aggregates is thoroughly investigated with appropriate simulations using the Discrete Dipole Approximation (DDA) method. The effect of parameters such as the overall radius of the nanostructure, the small nanosphere radius, and the distance between the nanospheres, on the extinction efficiency factor of the nanostructures was examined. The results indicate that the extinction spectra appear to depend heavily on the distance between the small nanospheres. Two distinct absorption peak wavelengths are observed for a specific nanostructure. The monolayer shell aggregate provides a reasonably tunable plasmon resonance wavelength while the small size of its components can be exploited for intracellular distribution.