Improved nanophotonic and plasmonic structures for sensing and molecular detection

29.10.2012, 13:30

Atef Shalabney, Department of Electrooptic Engineering, Ben Gurion University, Beer Sheva, Israel

Surface plasmon resonance (SPR) sensors have been a mature technology for more than two decades now, however, recent investigations show continuous enhancement of their sensitivity and their lower detection limit. Together with the recent investigations in localized SPR (LSPR) phenomena and surface-enhanced spectroscopies such as surface enhanced Raman scattering (SERS), drastic developments are expected to revolutionize the field of optical biosensing. Two modifications of the conventional SPR sensor based on the Kretschmann-Raether (KR) configuration are presented. First, the implications of adding a thin dielectric film with high refractive index (RI) on top of the metallic layer in the angular and spectral modes are demonstrated. Then, the potential of using metallic columnar thin films (CTF) is demonstrated as well. Our recent works showed that introducing thin dielectric layer in the SPR sensor, not only enhances the sensitivity of the sensor, but also improve the resolution of the measurement, facilitate sensing in the infrared region, and considerably contribute to the stability of the structure. Replacing the continuous film with the CTF, on the other hand, enhances both the angular and the spectral sensitivities and adds more degrees of freedom in designing evanescent waves based techniques. In order to model the CTF layers, the shapes of the nanostructures constituting the CTF are described as ellipsoidal inclusions in which the effective permittivity dyadic of the composite material is calculated using the Bruggeman formalism with exact depolarization dyadics. Finally the use of metallic sculptured thin films (STF) as substrates to enhance SERS from biomolecules will be presented. The STFs, which are assemblies of shaped and parallel nanostructures, prepared by the glancing angle deposition (GLAD) technique, exhibit remarkable plasmonic properties that make them a promising substrate for enhanced spectroscopies. The influences of the nanostructures' size, topology, the substrate features, and the preparation conditions on the enhancement of SERS were examined.