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Abstract: This work is focused on the fabrication of a human breathing sensor based on the in situ synthesis of silver nanoparticles (Ag-NPs) inside a polymeric coating previously deposited on an optical fiber core by means of the Layer-by-Layer self-assembly. The Ag-NPs were created using a synthesis protocol consisting of a loading step of the Ag+ cations into the polymeric film and a further reduction step using dimethylamine borane (DMAB). The morphology and distribution of the Ag-NPs inside the polymeric coating have been studied using atomic force microscopy (AFM). Furthermore, UV–VIS spectroscopy and energy dispersive X-ray (EDX) were also used to confirm the synthesis of the Ag-NPs within the resultant coating. The amount of Ag-NPs increases when the number of loading/reduction cycles is higher. Therefore the incorporation of the Ag-NPs affects the refractive index of the overlay promoting the observation of a resonant attenuation band in the infrared region (NIR), known as Lossy Mode Resonance (LMR), which can be used as a sensing signal to monitor the human breathing. The quality of the device has been experimentally tested with good sensitivity (0.455nm per RH%) and fast response time (692ms and 839ms for rise/fall). [Copyright &y& Elsevier]

Abstract: In this work, it is presented for the first time the fabrication and characterization of a novel optical fiber humidity sensor based on both Lossy-mode resonance (LMR) and Localized Surface Plasmon Resonance (LSPR). Those resonances were created using Layer-by-Layer (LbL) polymeric coating loaded with Ag nanoparticles (Ag NPs) and fabricated onto an optical fiber core. Firstly, it was observed a LSPR attenuation band, inherent to the presence of the Ag NPs in the coating. This LSPR band showed a slight intensity variation with Relative Humidity (RH) changes but no significant wavelength dependence was observed. Otherwise several LMR attenuation bands were observed in the 400–1100nm spectral range as the thickness coating was increased. The LMR maxima depend strongly on the thickness and refractive index of the LbL overlay, and therefore, they show a strong wavelength response to Relative Humidity (RH) changes. A wavelength-based optical humidity sensor was achieved and the dynamic range (42.4nm), transfer function, response time (476ms and 447ms for rise/fall respectively) were characterized. The results confirm that this sensor could be used even for monitoring human breathing. [Copyright &y& Elsevier]