We have fabricated gold nanospheres composite multilayer films using the layer-by-layer (LbL) self-assembly
technique, and have investigated the aggregate states of the gold nanosphere. The gold nanospheres composite
multilayer films were fabricated by controlling the gold nanosphere layers with polyelectrolyte layers, and
were characterized with linear and nonlinear optical spectroscopy. The transmission absorption spectra and
scanning electron microscopy (SEM) images show modifications of the optical properties arising from the aggregate
states of the gold nanospheres. The strong longitudinal resonance mode was observed when the gold
nanospheres form aggreagates. Intense optical second-harmonic generation (SHG) was observed from the gold
nanosphere aggregates of which surface was covered with a hemicyanine self-assembled monolayer. This high
SHG response originates from the strong interaction via localized surface plasmon enhancement of the gold
nanosphere aggregates. The gold nanosphere aggregates are promising for applications to optoelectronic devices
and surface-enhanced spectroscopy.
In this paper we will discuss a few basic concepts concerning the use of evanescent optical fields for the excitation of fluorescent chromophores placed near the interface. The observation of enhanced fluorescence from chromophores excited by surface plasmon and waveguide modes will be presented and discussed. We attribute the enhancement to the near-field interaction between the chromophores and the increased photonic mode density by surface plasmon and waveguide modes. We determined limits of detection (LOD) of DNA hybridisation using the same sensor architecture by surface plasmon fluorescence spectroscopy (SPFS) and optical waveguide fluorescence spectroscopy (OWFS). Both SPFS and OWFS techniques have the same detection principle using an enhanced electromagnetic field to excite fluorophores and make it possible to monitor DNA hybridisation in real-time with high sensitivity. The relative photonic mode density of each mode was calculated under the resonance condition, and these values are reflected in the LOD values.