Nanoporous thin films in optical waveguide spectroscopy for chemical analytics

• Autores: Knoll, Wolfgang; Azzaroni, Omar; Duran, Hatice; Kunze Liebhäuser, Julia; Lau, King Hang Aaron; Reimhult, Erik; Yameen, Basit
• Año de publicación: 2020
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: ANODIZATION; CHEMICAL AND BIOSENSING; COLLOID LITHOGRAPHY; E-BEAM LITHOGRAPHY; NANOPOROUS THIN FILMS; OPTICAL WAVEGUIDE SPECTROSCOPY; POLYMER NANOROD ARRAY
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

Spectroscopy with planar optical waveguides is still an active field of research for the quantitative analysis of various supramolecular surface architectures and processes, and for applications in integrated optical chip communication, direct chemical sensing, etc. In this contribution, we summarize some recent development in optical waveguide spectroscopy using nanoporous thin films as the planar substrates that can guide the light just as well as bulk thin films. This is because the nanoporosity is at a spacial length-scale that is far below the wavelength of the guided light; hence, it does not lead to an enhanced scattering or additional losses of the optical guided modes. The pores have mainly two effects: they generate an enormous inner surface (up to a factor of 100 higher than the mere geometric dimensions of the planar substrate) and they allow for the exchange of material and charges between the two sides of the solid thin film. We demonstrate this for several different scenarios including anodized aluminum oxide layers for the ultrasensitive determination of the refractive index of fluids, or the label-free detection of small analytes binding from the pore inner volume to receptors immobilized on the pore surface. Using a thin film of Ti metal for the anodization results in a nanotube array offering an even further enhanced inner surface and the possibility to apply electrical potentials via the resulting TiO2 semiconducting waveguide structure. Nanoporous substrates fabricated from SiNx thin films by colloid lithography, or made from SiO2 by e-beam lithography, will be presented as examples where the porosity is used to allow for the passage of ions in the case of tethered lipid bilayer membranes fused on top of the light-guiding layer, or the transport of protons through membranes used in fuel cell applications. The final example that we present concerns the replication of the nanopore structure by polymers in a process that leads to a nanorod array that is equally well suited to guide the light as the mold; however, it opens a totally new field for integrated optics formats for direct chemical and biomedical sensing with an extension to even molecularly imprinted structures. [Figure not available: see fulltext.]
Fil: Knoll, Wolfgang. Competence Centre for Electrochemical Surface Technology; Austria. Austrian Institute of Technology; Austria
Fil: Azzaroni, Omar. Competence Centre for Electrochemical Surface Technology; Austria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina
Fil: Duran, Hatice. University of Economics and Technology. Department of Materials Science and Nanotechnology Engineering; Austria
Fil: Kunze Liebhäuser, Julia. Universidad de Innsbruck; Austria
Fil: Lau, King Hang Aaron. University of Strathclyde; Reino Unido
Fil: Reimhult, Erik. University of Natural Resources and Life Sciences. Department of Nanobiotechnology; Austria
Fil: Yameen, Basit. Lahore University of Management Sciences. Syed Babar Ali School of Science and Engineering. Department of Chemistry and Chemical Engineering; Pakistán