Optically thick metallic nanohole structures were fabricated using two different methods – electron‐beam and nanosphere lithography. The nanosphere lithography technique was based on self‐assembling of polystyrene or silica nanospheres (0.560–1.25 μm in diameter) followed by the deposition of a silver film. The holes size and periodicity of the patterns as well as optical properties (transmission and reflection in the Visible–NIR) of the structures were investigated. The extraordinary optical transmission (EOT) was studied experimentally in both structures and it was found to be dependent on the geometrical parameters (holes shape, diameter and periodicity of structures). As the samples were made for long range order, the effect of the defects like missing holes, change of periodicity or variation of the holes shape, were also studied. The experimental results, especially the position of the SPR band in the different nanohole structures, were compared with those found by simulation carried out with 3D FDTD (finite difference time domain). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Monolayers and multilayers of polystyrene (PS)-gold composite films prepared by two different deposition methods have been investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and confocal Raman microspectroscopy. The intensity of the 1001 cm(-1) ring breathing mode of PS is used to evaluate the degree of ordering of monolayers and multilayers within a colloidal crystal. The depth profiling capability of confocal Raman microscopy is used to probe the regions inside the fractures in multilayered films. The intensity profile of the 1001 cm(-1) peak revealed the presence of fractures of different shapes with some PS microspheres at the bottom of the fracture. A strong increase in the Raman intensity (by 10(3) times) has been observed when probing the regions where Au nanoparticles are concentrated in aggregates of different shapes. This enhancement is attributed to the surface plasmons generated by the periodic structure of the gold nanoparticles.

An optical biosensor based on gold nanohole arrays was developed using a new nanosphere lithography technique. A vertical deposition method was used to deposit multilayers of a polystyrene (PS) -gold composite on a silanized glass substrate. The SEM images have shown that the gold nanohole and nanoring arrays are distributed uniformly on the substrate. The sensitivity of the gold Surface Plasmon Resonance (SPR) band to the environment was found to be dependent on the geometry of the array. The new nanostructures have been used as platforms for rapid screening of biomolecular interactions. Fibrinogen and biotin absorption studies conducted with the functionalized gold nanostructures demonstrated the feasibility of using them to monitor biomolecular interactions. The sensitivity was found to be around 300 nm·RIU -1 , which is adequate for biosensing applications. The present technique has the advantage of simplicity; the structures can be prepared without any special equipment and a standard cell can be used for optical measurements.