Optical fiber sensors based on gold nanorods embedded in polymeric thin films

Abstract

In this work, we present a study about the generation and analysis of optical resonances caused by gold nanorods (GNRs) embedded in films. GNRs were embedded in polymeric thin films using the Layer-by-Layer nanoassembly (LbL) deposition technique. Polymer/GNRs thin films of different thicknesses were deposited on the surface of cladding removed optical fibers for sensing. The spectral responses of the optical fiber sensors were monitored during the build-up of the thin films. The generation of two Localized Surface Plasmon Resonances (LSPRs) associated to the GNRs was observed in thinner coatings. These devices with around 12 polymer/GNRs bilayers were characterized as refractometers, providing an intensity-based sensitivity up to 75.69dB/RIU. For thicker polymer/GNRs overlays, both LSPRs bands were also generated and, additionally, it was observed a new Lossy Mode Resonance (LMR) band due to modes coupled to the sensitive coating. The dependence of these three resonance bands with the surrounding refractive index was studied. Finally, these sensors were tested in a climatic chamber in the 20–90% relative humidity (RH) range and the LMR showed a good sensitivity to RH changes while the LSPR bands remained very stable in comparison. Results showed an excellent sensitivity of 11.2nm/%RH for the LMR, confirming the potential of this type of optical fiber sensor based on the combination of LSPRs and LMRs bands.