Localized Surface Plasmon Resonance for Optical Fiber-Sensing Applications

It is well known that optical fiber sensors have attracted the attention of scientific community due to its intrinsic advantages, such as lightweight, small size, portability, remote sensing, immunity to electromagnetic interferences and the possibility of multiplexing several signals. This field has shown a dramatic growth thanks to the creation of sensitive thin films onto diverse optical fiber configurations. In this sense, a wide range of optical fiber devices have been successfully fabricated for monitoring biological, chemical, medical or physical parameters. In addition, the use of nanoparticles into the sensitive thin films has resulted in an enhancement in the response time, robustness or sensitivity in the optical devices, which is associated to the inherent properties of nanoparticles (high surface area ratio or porosity). Among all of them, the metallic nanoparticles are of great interest for sensing applications due to the presence of strong absorption bands in the visible and near-infrared regions, due to their localized surface plasmon resonances (LSPR). These optical resonances are due to the coupling of certain modes of the incident light to the collective oscillation of the conduction electrons of the metallic nanoparticles. The LSPR extinction bands are very useful for sensing applications as far as they can be affected by refractive index variations of the surrounding medium of the nanoparticles, and therefore, it is possible to create optical sensors with outstanding properties such as high sensitivity and optical self-reference. In this chapter, the attractive optical properties of metal nanostructures and their implementation into different optical fiber configuration for sensing or biosensing applications will be studied

Optical Fiber Sensors Based on Nanoparticle-Embedded Coatings

The use of nanoparticles (NPs) in scientific applications has attracted the attention of many researchers in the last few years. The use of NPs can help researchers to tune the physical characteristics of the sensing coating (thickness, roughness, specific area, refractive index, etc.) leading to enhanced sensors with response time or sensitivity better than traditional sensing coatings. Additionally, NPs also offer other special properties that depend on their nanometric size, and this is also a source of new sensing applications. This review focuses on the current status of research in the use of NPs within coatings in optical fiber sensing. Most used sensing principles in fiber optics are briefly described and classified into several groups: absorbance-based sensors, interferometric sensors, fluorescence-based sensors, fiber grating sensors, and resonance-based sensors, among others. For each sensor group, specific examples of the utilization of NP-embedded coatings in their sensing structure are reported

Hybrids Provide More Options for Fine-Tuning Flowering Time Responses of Winter Barley

Crop adaptation requires matching resource availability to plant development. Tight coordination of the plant cycle with prevailing environmental conditions is crucial to maximizing yield. It is expected that winters in temperate areas will become warmer, so the vernalization requirements of current cultivars can be desynchronized with the environment’s vernalizing potential. Therefore, current phenological ideotypes may not be optimum for future climatic conditions. Major genes conferring vernalization sensitivity and phenological responses in barley (Hordeum vulgare L.) are known, but some allelic combinations remain insufficiently evaluated. Furthermore, there is a lack of knowledge about flowering time in a hybrid context. To honor the promise of increased yield potentials, hybrid barley phenology must be studied, and the knowledge deployed in new cultivars. A set of three male and two female barley lines, as well as their six F1 hybrids, were studied in growth chambers, subjected to three vernalization treatments: complete (8 weeks), moderate (4 weeks), and low (2 weeks). Development was recorded up to flowering, and expression of major genes was assayed at key stages. We observed a gradation in responses to vernalization, mostly additive, concentrated in the phase until the initiation of stem elongation, and proportional to the allele constitution and dosage present in VRN-H1. These responses were further modulated by the presence of PPD-H2. The duration of the late reproductive phase presented more dominance toward earliness and was affected by the rich variety of alleles at VRN-H3. Our results provide further opportunities for fine-tuning total and phasal growth duration in hybrid barley, beyond what is currently feasible in inbred cultivars.his research was supported by the contract “Iberia region hybrid barley variety development and understanding effects of adaptation genes in hybrids,” between CSIC and Syngenta (Basel, Switzerland) Crop Protection AG, which included funding for MF-C scholarship

Comparative study of polymeric matrices embedding oxygen-sensitive fluorophores by means of Layer-by-Layer nanosassembly

In this work, a comparative study of luminescent optical fiber oxygen sensors fabricated by means of Layer-by-Layer nanoassembly technique (LbL) has been carried out. The oxygen-sensitive fluorophore is the same in all the cases, the metalloporphyrin platinum tetrakis pentafluorophenylporphin (Pt-TFPP), which was deposited using LbL method by entrapping it into anionic micelles formed with a surfactant. As cationic counterpart to form the anionic-cationic bilayer, different polyelectrolytes acting as the polymeric matrices embedding the sensing material have been studied: poly(diallyldimethylammonium chloride) (PDDA), polyethyleneimine (PEI) and poly(allylamine hydrochloride) (PAH). Absorbance spectra, contact angle, Atomic Force Microscope and Scanning Electronic Microscope analysis were performed on the sensing films. The kinetics, resolution and sensitivity of the sensors for different number of bilayers were also determined. It has been found a remarkable difference on these characteristics depending on the polymer used

A comparative study of two different approaches for the incorporation of silver nanoparticles into layer-by-layer films

UPNa. Departamento de Ingeniería Eléctrica y Electrónica. Laboratorio de Dispositivos Ópticos NanoestructuradosIn this work, a comparative study about the incorporation of silver nanoparticles (AgNPs) into thin films is presented using two alternative methods, the in situ synthesis process and the layer-by-layer embedding deposition technique. The influence of several parameters such as color of the films, thickness evolution, thermal post-treatment, or distribution of the AgNPs along the coatings has been studied. Thermal post-treatment was used to induce the formation of hydrogel-like AgNPs-loaded thin films. Cross-sectional transmission electron microscopy micrographs, atomic force microscopy images, and UV-vis spectra reveal significant differences in the size and distribution of the AgNPs into the films as well as the maximal absorbance and wavelength position of the localized surface plasmon resonance absorption bands before and after thermal post-treatment. This work contributes forThis work was supported by the Spanish Ministry of Economy and Competitiveness through TEC2010-17805 Research Project, Innocampus Program and Public University of Navarra (UPNA) research grants

Lossy mode resonance optical fiber sensor to detect organic vapors

Trabajo presentado al 14th International Meeting on Chemical Sensors celebrado en Nuremberg (Alemania) del 20 al 23 de mayo de 2012.A transmission sensor able to detect Volatile Organic Compounds (VOCs) has been developed using optical fiber with Plastic Cladding (PCS). Specifically, 1.5 cm of the cladding was removed: along this section, polymer nanolayers were deposited by means of the Layer-by-Layer method (LbL). This structure was doped with an organometallic material sensitive to VOCs. In this manner, Lossy Mode Resonances (LMRs) were induced in the transmission spectra of the sensor showing a wavelength shift as the nano structure grown. The sensing material accelerated the LMRs appearance with respect to the nanolayers without additive reported in previous works, and also, its spectral shift. Once the construction process was completed, two LMRs were observed: the first one was located at 778 nm and the second one at 463 nm. In presence of ethanol vapors, the sensor spectrum varied, showing the first LMR peak a remarkable shift of 100 nm. This behavior is reversible and was also registered for isopropanol vapors. The sensor response was analyzed as well for different concentrations of ethanol vapors.The authors would like to acknowledge the financial support from the Spanish Ministerio de Educación y Ciencia through projects TEC2010-17805 and TEC2010-20224-C02-01.Peer Reviewe

Self-referenced optical fiber sensor for hydrogen peroxide detection based on LSPR of metallic nanoparticles in layer-by-layer films

Intensity-based optical fiber sensors are one of the most studied sensor approaches thanks to their simplicity and low cost. Nevertheless, their main issue is their lack of robustness since any light source fluctuation, or unexpected optical setup variation is directly transferred to the output signal, which, significantly reduces their reliability. In this work, a simple and robust hydrogen peroxide (H2O2) optical fiber sensor is proposed based on the Localized Surface Plasmon Resonance (LSPR) sensitivity of silver and gold metallic nanoparticles. The precise and robust detection of H2O2 concentrations in the ppm range is very interesting for the scientific community, as it is a pathological precursor in a wide variety of damage mechanisms where its presence can be used to diagnose important diseases such as Parkinson's disease, diabetes, asthma, or even Alzheimer's disease). In this work, the sensing principle is based the oxidation of the silver nanoparticles due the action of the hydrogen peroxide, and consequently the reduction of the efficiency of the plasmonic coupling. At the same time, gold nanoparticles show a high chemical stability, and therefore provide a stable LSPR absorption band. This provides a stable real-time reference that can be extracted from the spectral response of the optical fiber sensor, giving a reliable reading of the hydrogen peroxide concentration.This work has been supported by the Spanish Economy and Competitiveness TEC2016-78047-R grant and the PhD research grants of the Public University of Navarre

Simultaneous measurement of humidity and temperature based on a partially coated optical fiber long period grating

A humidity and temperature optical fiber sensor based on a long-period grating (LPG), which can provide simultaneous response to both magnitudes, is proposed and demonstrated via experiments. Previously, the LPG was fully coated with humidity sensitive nanostructured polymeric thin films by the Layer-by-Layer (LbL) nano assembly technique. Hence the surrounding refractive index was changed, so provoking wavelength shifts of the attenuation bands of the transmission spectrum. This fully coated LPG was exposed to relative humidity (RH) and temperature tests, varying from 20% to 80% RH and from 25 to 85ºC, respectively. Then, half of the LPG coating was chemically removed and this results in the splitting of the main attenuation band into two different contributions. When this semi-coated LPG was also exposed to RH and temperature tests, the new two attenuation bands presented different behaviors for humidity and temperature. This novel dual-wavelength based sensing method enables the simultaneous measurement of RH and temperature using only one LPG.This work was supported in part by the Spanish Ministry of Economy and Competitiveness - through the projects CICYT-FEDER TEC2013-43679-R and TEC2014-60378-C2-1-R. It was also supported by a UPNA pre-doctoral research grant, by the Program of International Excellence Campus VLC/Campus, by the grant of program SANTIAGO GRISOLIA, and by the Research Excellency Award Program GVA PROMETEO 2013/012.Urrutia, A.; Goicoechea, J.; Ricchiuti, AL.; Barrera Vilar, D.; Sales Maicas, S.; Arregui, FJ. (2016). Simultaneous measurement of humidity and temperature based on a partially coated optical fiber long period grating. Sensors and Actuators B: Chemical. 227(5):135-141. https://doi.org/10.1016/j.snb.2015.12.031S135141227