Nanostructured Optical Waveguides for Thin-Film Characterization

In this review, we summarize some of our efforts in parallel with other research groups' studies in designing, assembling, and structurally and functionally characterizing nanostructured materials using optical waveguide spectroscopy (OWS). We focus on the study of porous nanostructures: (i) cylindrical thin films (ii) mesoporous thin films, and (iii) nanorod arrays as optical waveguides for high sensitivity biosensing. We discuss the waveguiding properties of these thin films in the visible wavelengths and theoretical description of nanostructured hybrid optical waveguides by effective medium theory (EMT). We demonstrate how high sensitivity can be achieved by modifying pore walls with small functional groups (i.e. silanes) as well as polypeptide brushes. When using also mesoporous semiconducting materials (TiO2) hybrid architectures, simultaneous measurement of OWS and electrochemistry can be possible with very interesting photophysical properties that can be useful also for solar-cell applications. Other strategies for using the anodic aluminum oxide (AAO) layers as a template mold include the growth of metal or polymeric nanorod arrays from different functional monomers that after the dissolution of the template are still able to guide light. This opens up novel concepts for integrated optics platforms with nanostructured materials.