BUSCADOR RECOLECTA

The objective of this Letter consists of the exploration of the lossy mode resonance (LMR) phenomenon beyond the nearinfrared region and specifically in the short wave infrared region (SWIR) and medium wave infrared region (MWIR). The experimental and theoretical results show for the first time, to the best of our knowledge, not only LMRs in these regions, but also the utilization of fluoride glass optical fiber associated with this phenomenon. The fabricated devices consist of a nanometric thin-film of titanium dioxide used as LMR generating material, which probed extraordinary sensitivities to external refractive index (RI) variations. RI sensitivity was studied in the SWIR and MWIR under different conditions, such as the LMR wavelength range or the order of resonance, showing a tremendous potential for the detection of minute concentrations of gaseous or biological compounds in different media., Ministerio de Ciencia, Innovación y Universidades (FPU18/03087); Agencia Estatal de Investigación (PID2019-106231RB-I00 TEC); Universidad Pública de Navarra.

A micro sized interdigital capacitor sensible to CO2 and NO is
studied in this work. The photolithography technique enables to obtain fingers
with dimensions of 10 × 500 µm and separated 7 µm between them. The
deposition of a film composed of graphene oxide particles as the dielectrics of
the capacitor allows to measure the gas concentration of CO2 and NO mixed
with N2. The sensors were characterized in a gas chamber with a constant flow,
obtaining promising results in changes of capacitance at 100 Hz. The sensors
have a good linearity and sensitivity with a R2 = 0.996 and 5.026·10-1 pF/ % v/v
for CO2 and R2=0.972 and 1.433·10-1 pF/ppb for NO., This research was funded Agencia Estatal de Investigación (PID2019-106231RB-I00 and PID2021-122613OB-100) the Ministry of Science, Innovation and Universities of Spain (PRE2020-091797 and PEJ2018-002958-P) and Institute of Smart Cities PhD Student grants.

Devices based on the lossy mode resonance (LMR) effect have found numerous sensing applications. Herein, the enhancement of the sensing properties by the introduction of an intermediate layer between the substrate and the LMR-supporting film is discussed. Experimental results for a silicon oxide (SiO2) layer of tuned thickness between a glass slide substrate and a thin film of titanium oxide (TiO2) prove the possibility of significantly increasing the LMR depth and the figure of merit (FoM) for refractive index sensing applications, which is supported by a numerical analysis using the plane wave method for a one-dimensional multilayer waveguide. The application of the intermediate layer allows the introduction of a new, to the best of our knowledge, degree of freedom into the design of LMR-based sensors, resulting in improved performance for demanding fields such as chemical sensing or biosensing., Agencia Estatal de Investigación (PID2019-106231RB-100); Universidad Pública de Navarra; Narodowe Centrum Badań i Rozwoju (TECHMATSTRATEG-III/0042/2019).

A fiber Bragg grating patterned on a SnO2 thin film deposited on the flat surface of a D-shaped polished optical fiber is studied in this work. The fabrication parameters of this structure were optimized to achieve a trade-off among reflected power, full width half maximum (FWHM), sensitivity to the surrounding refractive index (SRI), and figure of merit (FOM). In the first place, the influence of the thin film thickness, the cladding thickness between the core and the flat surface of the D-shaped fiber (neck), and the length of the D-shaped zone over the reflected power and the FWHM were assessed. Reflected peak powers in the range from −2 dB to −10 dB can be easily achieved with FWHM below 100 pm. In the second place, the sensitivity to the SRI, the FWHM, and the FOM were analyzed for variations of the SRI in the 1.33–1.4 range, the neck, and the thin-film thickness. The best sensitivities theoretically achieved for this device are next to 40 nm/RIU, while the best FOM has a value of 114 RIU−1., This work has been supported by the Spanish Ministry of Universities through the FPU18/03087 grant (Formación de Profesorado Universitario) and the Spanish Ministry of Science and Innovation PID2019-106231RB-I00 TEC Research fund.

Functionalization plays a crucial role in the development of biosensors. In this study, bioreceptors were directly immobilized onto the surface of a sensing layer after physical activation, avoiding the need for longer and more complex functionalization systems. This direct immobilization was applied to an optical sensing platform based on lossy mode resonances (LMRs) generated by a thin-film of titanium (IV) dioxide/poly(sodium 4-styrenesulfonate) (TiO 2 /PSS). To generate the LMR, a 200-micron bare optical fiber was coated with TiO 2 /PSS using the layer-by-layer self-assembly technique. The PSS of the sensing layer was then physically activated using either UV-ozone or plasma to immobilize anti-rabbit IgG bioreceptors. This enabled specific and label-free detection of rabbit IgG concentrations ranging from 0.002 to 2 mg/ml. The results presented in this work include real-time detection of rabbit IgG, a comparison between the two activation techniques (UV-ozone and plasma), and an analysis of the biosensor’s reusability over four consecutive cycles, which demonstrates the promising potential of the TiO 2 /PSS sensing layer for biosensing applications., This work was supported in part by the Spanish Agencia Estatal de Investigación (AEI) under Grant PID2019-106231RB-I00, in part by the Public University of Navarra under Grant
PJUPNA2033 and in part by a Ph.D Grant by the Public University of Navarra.

The mode transition is a phenomenon observed in
thin film coated long period fiber gratings (LPGs) and singlemode multimode single-mode (SMS) fibers for certain values of
the coating thickness and refractive index, resulting in increased
sensitivity for sensing applications. It is shown here that mode
transitions occur simultaneously for a large number of mode
resonances in the transmission spectra of tilted fiber Bragg
gratings (TFBG) measured during the deposition of ~350nm thick
TiO2 coatings by Atomic Layer Deposition (ALD). In TFBGs, the
mode transition shows up as an acceleration of the resonance
wavelength shift vs thickness, but without fading of the resonance
amplitude. Furthermore, the results show that the mode transition
for cladding modes with predominantly “TE” polarization at the
cladding boundary is significantly sharper than that of
predominantly “TM” polarized modes and that it occurs at a
smaller coating thickness (<100 nm vs >200 nm). Finally, using a
separately determined coating refractive index (2.14, by
ellipsometry on witness flats deposited simultaneously) and
simulations of the resonance shifts of the TFBG with coating
thickness, it is demonstrated that a TFBG connected to a spectral
interrogation system can be used to measure the growth of a
coating on the surface of the fiber in real time., This work was supported in part by the Spanish Ministry, Formación de Profesorado Universitario under Grant FPU18/03087, in part by the Spanish
Ministry of Science and Innovation through TEC Research fund under Grant PID2019-106231RB-I00, and in part by NSERC under Grant RGPIN-2019-
06255.

A micro sized interdigital capacitor has been proposed for the detection of relative humidity. The photolithography technique enables the fabrication of fingers with a size of 10x500 um. A thin film of agarose functionalizes the sensor for humidity sensing, which improves its performance by 155 times, obtaining a sensitivity of 32.98 pF/%RH., This research was funded by the Ministry of Science, Innovation and Universities of Spain (PRE2020-091797, PEJ2018-002958-P and PID2019-106231RB-I00) and the Institute of Smart Cities PhD Student grants

Los sensores basados en resonancias ópticas han incrementado su popularidad estos últimos años. Cobran especial relevancia en aplicaciones como la detección de gases gracias a su alta sensibilidad y robustez en ambientes agresivos.
Esta tesis ha contribuido a la mejora de sensores de gases basados en resonancias ópticas empleando dos enfoques; la búsqueda de materiales sensibles a gases y el desarrollo de nuevas técnicas de interrogación. Los materiales investigados están formados por una matriz polimérica con materiales nanoestructurados: nanopartículas de óxido tungsteno, nanodiamantes y nanosheets de óxido de grafeno. Las propiedades de estos materiales son testeadas ante diferentes gases e índices de refracción externo (surrouding refractive index SRI).
En la búsqueda de sensores ultrasensibles al SRI, se desarrollan dos líneas de investigación. Una estudia el efecto LMR y su sensibilidad en la región de infrarrojo medio (MIR) empleando fibras ópticas fluoradas y TiO2 como material. La otra, se centra en resonancias acuñadas por primera como surface exciton polariton resonance (SEPR) basándose en el efecto long range surface exciton polariton (LRSEP). Para ello se desarrolla un sensor en configuración Kretschmann-Raether con dos películas de Cr y MgF2. También se estudia los papeles de los distintos parámetros del sensor, así como experimentalmente la sensibilidad al ángulo de incidencia y SRI., Sensors based in optical resonances have increased their popularity in the last years. The ones used in gas measurement applications are especially relevant, due to their high sensitivity and robustness to harsh environments.
This thesis has contributed to the improvement of gas sensors based in optical resonances employing two approaches: the search for gas-sensitive materials and the development of new interrogation techniques. The researched materials are composed by a polymeric matrix and nanostructured materials: tungsten oxide nanoparticles, nanodiamonds and graphene oxide nanosheets. The properties of these materials are studied with different gas concentrations and surrounding refractive indexes (SRI).
Two research lines are developed to obtain ultrasensitive sensors to SRI. The first one studies the LMR effect and its sensitivity in the mid infrared (MIR) region, employing fluoride glass optical fibers and TiO2 as material. The second one focuses on the resonances coined for the first time as surface exciton polariton resonances (SEPR) that are based on the long range surface exciton polariton (LRSEP) effect. A sensor in a Krestchmann-Raether configuration is developed with two films of Cr and MgF2. The roles of the different parameters of the sensor are studied theoretically as well as the experimental sensitivity to the incident angle and SRI., Instituto de Smart Cities de la Universidad Pública de Navarra (Contratos Pre-doctorales adscritas a Grupos e Institutos de Investigación de la Universidad Pública de Navarra); Ministerio de Ciencia e Innovación (PID2019-106231RB-I00 TEC); Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-78047-R); convocatoria ATTRACT financiada por el programa de investigación e innovación Horizon 2020 de la Unión Europea (subvención No 777222); Universidad Pública de Navarra (PJUPNA26)., Programa de Doctorado en Ciencias y Tecnologías Industriales (RD 99/2011), Industria Zientzietako eta Teknologietako Doktoretza Programa (ED 99/2011)

Esta tesis se enfoca en explotar el fenómeno de resonancia por modos con pérdidas (LMR) hacia
el desarrollo de aplicaciones que van más allá de la detección de un solo parámetro con una fibra
óptica. Después de una introducción al campo, en el capítulo dos se propone la estructura de guía de
onda plana como una configuración alternativa y ventajosa para soportar varios tipos de sensores
basados en LMR. Después de eso, en el capítulo 3 se explora en detalle el concepto multiparamétrico
y las estrategias para mejorar la sensibilidad del fenómeno óptico con muchas simulaciones y
resultados experimentales. Los capítulos finales profundizan en la combinación de LMR con otras
técnicas de detección clásicas, como sensores acústicos de superficie (SAW) y electroquímica (EC),
proporcionando información complementaria útil., This thesis focuses on exploiting the lossy mode resonance phenomenon towards development of
applications that go beyond the single parameter detection with an optical fiber. After an introduction
to the field, in chapter two the planar waveguide structure is proposed as an alternative and
advantageous configuration to support various types of sensors based on lossy mode resonances
(LMR). After that, in chapter 3 the multiparametric concept and strategies to enhance the sensitivity
of the optical phenomenon are explored in detail with many simulations and experimental results. The
final chapters delve deeper into the combination of LMR with other classical detection techniques,
such as surface acoustic sensors (SAW) and electrochemistry (EC), providing useful complementary
information., La realización de este trabajo ha sido posible gracias a las aportaciones económicas recibidas por
parte de la Universidad Pública de Navarra (UPNA), así como del patrocinio de la UPNA y del Ministerio
de Ciencia e Innovación de España a través de los proyectos I+D+i 'Retos Investigación' PID2019-106231RB-I00 y PID2019-106070RB-I00., Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011), Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011)

This letter presents the fabrication of dual lossy mode resonance (LMR) refractometers based on titanium dioxide (TiO2) and tin oxide (SnO2) thin films deposited on a single side-polished D-shaped optical fiber. For the first time, to the best of our knowledge, two independent LMRs are obtained in the same D-shaped optical fiber, by using a step-shaped nanostructure consisting of a first section of TiO2 with a thickness of 120 nm and a second section with a thickness of 140 nm (120 nm of TiO2 and 20 nm of SnO2). Each section is responsible for generating a first-order LMR with TM-polarized light (LMRTM). TiO2 is deposited by atomic layer deposition and SnO2 by electron-beam deposition. The theoretical results show that the depth of each of the resonances of the dual LMR depends on the length of the corresponding section. Two experimental devices were fabricated with sections of different lengths, and their sensitivities were studied, achieving values ∼ 4000 nm/refractive index unit (RIU) with a maximum of 4506 nm/RIU for values of the SRI between 1.3327 and 1.3485., Ministerio de Ciencia, Innovación y Universidades (FPU18/03087); Agencia Estatal de Investigación (PID2019-106231RB-I00).

A new thermal expansion sensor is presented in this letter. It combines an interferometric fiber sensor and an erbium-doped fiber ring laser as the light source. The sensor consists of a combination of single-mode, hollow-core, and no-core mirror fibers. The sensor was tested on two different types of based metal, such as aluminum and steel, giving sensitivities as high as 38.7 and 5.75 nm/°C, respectively, showing good performance., This work was supported by the National Research Agency through Spanish project under Grant PID2019-106231RB-I00.

Development of miRNA optical biosensors for disease diagnosis and monitoring has acquired relevance in recent years, due to the clinical importance of miRNA and the inherent advantages of optical sensors. Here, we present the utilization of a fiber optic sensor based on Lossy Mode Resonance (LMR) for the detection of miRNA hsa-miR-223, a promising biomarker for the diagnosis of rheumatoid arthritis (RA)., This research was funded by the Spanish Agencia Estatal de Investigación (AEI) (PID2019-106231RB-I00), the Public University of Navarra (PJUPNA26), and the Spanish Ministry of Universities (FPU18/03087). In addition, this project has received funding from the ATTRACT call financed by the European Union's Horizon 2020 research and innovation program under grant agreement No 777222.

Lossy mode resonance (LMR)-based optical sensors change their wavelength upon contact with substances or gases. This allows developing applications to detect the refractive index of the surrounding medium and even the thickness of the biolayers deposited on the waveguide. In the same way, when acoustic sensors are in contact with a liquid, it is possible to determine parameters, especially mechanical ones such as shape of the particle or molecule, mass load, elastic constants and viscosity of the liquid. This work reports the development of a system that combines LMR with surface acoustic wave (SAW) technologies to characterize a liquid in terms of its refractive index and viscosity simultaneously. Conveniently prepared glucose solutions are used for sensor calibration. The refractive index of the solutions ranges from 1.33 to 1.41 and its viscosity ranges from 1.005 mPa·s to 9 mPa·s, respectively. A sensitivity of 332 nm per RIU has been achieved with the optical sensor while the acoustic sensor has shown a sensitivity of −1.5 dB/(mPa·s). This new combinational concept could be expanded to the development of more demanding applications such as chemical sensors or biosensors., The authors would like to acknowledge the partial support to the Spanish Ministry of Economy and Competitiveness PID2019-106070RB-I00 and PID2019-106231RB-I00 research funds and the pre-doctoral research grant of the Public University of Navarra.

Alzheimer’s disease (AD) is one of the most common neurodegenerative illnesses
displaying the highest death rate in the elderly. However, the existing AD
diagnostic system remains elusive due to lack of a technology that may ensure
enough sensitivity and reproducibility, detection accuracy, and specificity.
Herein, a straightforward approach is reported to realize lab-on-fiber (LoF)
technology for AD biomarker detection based on a D-shaped single-mode fiber
combined with nanometer-scale metal-oxide film. The proposed sensing system,
which permits the generation of lossy-mode resonance (LMR), remarkably
increases the evanescent field of light guided through the fiber, and hence the
fiber-surrounding medium interaction. Moreover, such optical sensors are highly
repeatable in results and can safely be embedded into a compact and stable
microfluidic system. Herein, the specific detection of Tau protein (as one of the
classical AD biomarkers that is highly correlated with AD progression) in a
complex biofluid with a detection limit of 10 12 M and over a wide concentration
range (10 3
–10 μg mL 1
) is successfully demonstrated. The proposed LoF
biosensor is an appealing solution for rapid, sub-microliter dose and highly
sensitive detection of analytes at low concentrations, hereby having the potential
toward early screening and personalized medicine in AD., F.C. gratefully acknowledges the support of the National Research Council of Italy (CNR) for the Short-Term Mobility programs 2017 and 2019. I.D.V. and I.R.M. acknowledge partial support of the Spanish Ministry of Economy and Competitiveness (Nos.TEC2016-79367-C2-2-R and PID2019-106231RB-I00), the predoctoral research grants of the Public University of Navarra and the Public University of Navarra grant PJUpna1936. E.S. and J.F-I. acknowledge partial support of the Spanish Ministry of Science, Innovation and Universities (PID2019-110356RB-I00/AEI/10.13039/501100011033). T.G.gratefully acknowledges the support of the National Natural Science Foundation of China (Nos. 62035006, 61975068, and 62011530459), the Guangdong Outstanding Scientific Innovation Foundation (No.2019TX05X383), and the Program of Marine Economy Development Special Fund (Six Marine Industries) under Department of Natural Resources of Guangdong Province (No. GDNRC [2021]33).

As an alternative to the different technologies that permit the detection of in-situ ice formation on different surfaces, this contribution proposes the design of an etched single-mode – multimode – single-mode (E-SMS) fiber-optic-based structure as a multimode interference refractometer. This sensor provides enhanced properties with respect to a basic SMS structure, including a higher sensitivity and periodical interferometry bands that can measure surrounding refractive indices with repeatability and robustness. Since ice and water refractive indices are sufficiently different, this structure has been used to detect the freezing - thawing process of water taking place inside a freezer between -20°C and +20°C. Also, this work intends to show a proof of concept of a simple technology that can be applied in different situations, such as in smart cities, avionics, structural health monitoring or even to avoid a cold chain breakage. Inside, novel developments to better understand the working operation of the E-SMS structure are shown, together with a study on how to correlate optical and thermal measurements from a refractive index point of view., This work was supported by the Spanish National Research Agency project with reference PID2019-106231RB-I00. Also, part of the funding was provided by the European Union's Horizon 2020 Research and Innovation Programme (Stardust-Holistic and Integrated Urban Model for Smart Cities) under Grant 774094. (Corresponding author: Abián B. Socorro-Leránoz).

A new type of resonance in the development of sensors using long-range surface exciton polariton (LRSEP) phenomena has been coined: surface exciton plasmon resonance (SEPR). The resonance was obtained in the reflected spectrum of a Kretschmann-Raether setup with a two-coupled-interface structure composed of 412 nm magnesium fluoride and 50 nm chromium thin films. The roles of different parameters such as thicknesses of the films and the incidence angles have been simulated. Some preliminary experimental results show a promising performance with a shift of the resonance central wavelength with changes in the incidence angle of -136.52 nm/° and a sensitivity of 23,221 nm/refractive index unit., This research was funded by Agencia Estatal de Investigacion (PID2019-106231RB-I00, the Institute of Smart Cities PhD Students grantes, the Ministry of Science, Innovation and Universities of Spain (FPU18/03087) and Margarita Salas-UPNA program (funded by the European Union-NextGenerationEU).

The mode transition phenomenon is experimentally demonstrated in tilted fiber Bragg gratings (TFBG) through the deposition of an indium tin oxide (ITO) thin film employing a DC sputtering machine., The authors would like to acknowledge the Spanish Ministry of Universities the support of this work through FPU18/03087 grant, the Spanish Ministry of Science and Innovation PID2019-106231RB-I00 TEC Research fund and NSERC grant RGPIN-2019-06255.

Lossy mode resonance (LMR)-based sensors have attracted much interest during the last decade in the domain of optical fiber (OF). Here, it is shown that the progress made in the transfer of this technology to planar waveguides (PWs) with different sensing applications such as environmental sensors and biosensors. In addition, the inherent advantages in terms of robustness, simplicity, and easiness to generate novel complex structures are discussed., This work was supported in part by the Agencia Estatal de Investigación under Grant PID2019-106231RBI00 Research Fund and in part by the STARDUST Project (European
Commission) under Grant H2020.

Los sensores de fibra óptica han experimentado un importante progreso en los últimos años con el empleo de estructuras basadas en redes de Bragg, interferómetros o resonancias electromagnéticas, entre otras y el desarrollo de la nanotecnología, que ha permitido la deposición de recubrimientos a nivel micro y nanométrico sobre la fibra. Estos avances han posibilitado la fabricación de sensores de fibra óptica para medir variables físicas, parámetros químicos o aplicaciones de biosensado.
Esta tesis contribuye al análisis y optimización, tanto teórica como experimental, de diferentes configuraciones y estructuras en fibra óptica, aplicadas al desarrollo de sensores. En esta tesis se estudian varias estructuras, incluidas las Lossy Mode Resonances (LMRs) y redes en fibra óptica: FBGs (redes de Bragg en fibra), LPGs (redes de período largo en fibra) y TFBGs (redes de Bragg inclinadas en fibra). Las principales líneas de investigación que se presentan en esta tesis son la fabricación de dispositivos multisensores basados en LMRs y la mejora del fenómeno de la mode transition en redes de fibra óptica: LPGs en fibras con doble cladding y TFBGs. El elemento común entre ambas líneas de investigación es el empleo de películas delgadas de materiales de alto índice de refracción: óxido de estaño (SnO2), óxido de indio y estaño (ITO) y dióxido de titanio (TiO2). Los resultados mostrados en esta tesis revelan el potencial de combinar varias estructuras y/o fenómenos en fibras ópticas para mejorar el desempeño de los sensores de fibra óptica., Optical fiber sensors have experienced an important progress in recent years with the employment of structures based on gratings, interferometers or electromagnetic resonances, among others; and the development of nanotechnology, that has enabled the deposition of coatings at the micro- and nanometric level on the fiber. These advances have allowed the manufacture of optical fiber sensors for measuring physical variables, chemical parameters or biosensing applications.
This thesis contributes to the analysis and optimization, both theoretical and experimental, of different configurations and structures in optical fiber, applied to the development of sensors. Several structures are studied in this thesis, including Lossy Mode Resonances (LMRs) and optical fiber gratings: FBGs (fiber Bragg gratings), LPGs (long period fiber gratings) and TFBGs (tilted fiber Bragg gratings). The main research lines that are presented in this thesis are the fabrication of multisensing devices based on LMRs and the enhancement of the mode transition in optical fiber gratings: LPGs in double clad fibers and TFBGs. The common element between both research lines is the employment of thin films of high refractive index materials: tin oxide (SnO2), indium tin oxide (ITO) and titanium dioxide (TiO2). The results shown in this thesis reveal the potential of combining several structures and/or phenomena in optical fibers to improve the performance of optical fiber sensors., El desarrollo de esta tesis ha sido posible gracias al apoyo financiero del Ministerio de Universidades (beca FPU18/03087), el Ministerio de Ciencia e Innovación (PID2019-106231RB-I00 TEC), el Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-78047-R), la convocatoria ATTRACT financiada por el programa de investigación e innovación Horizon 2020 de la Unión Europea (subvención No 777222) y la Universidad Pública de Navarra (PJUPNA26)., Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011), Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011)

Cyclic transparent optical polymer (CYTOP) fiber, used mainly in strain detection and refractive index characterization of liquids, can be polished for the detection of ultraviolet (UV) light radiation. The study investigates the transmission spectra of CYTOP fiber exposed to different intensities of UV light, demonstrating a linear relationship. A simplified system using a single wavelength, i.e., 395 nm, shows real-time performance of the sensor in a range from 1 to 15 mW. The results reveal the potential of CYTOP fiber as a UV sensor with a sensitivity of 0.65%/mW and a limit of detection of 0.3 mW, offering implications for monitoring UV radiation exposure and related health risks. In addition, the effect of the UV light was also observed at longer wavelengths with a lower intensity variation, which suggests that CYTOP fiber could be used for transmitting the UV radiation detection in telecommunications bands., This work was supported by the Spanish Agencia Estatal de Investigación (AEI) through Project PID2019-106231RB-I00. The work of Desiree Santano was supported by the Public University of Navarre through a predoctoral research grant. The work of Juan David López-Vargas was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001 (“doutorado sanduiche”). Open Access provided by Universidad Pública de Navarra within the CRUI CARE Agreement

Este trabajo de tesis se centra en el desarrollo y la optimización de biosensores de fibra óptica basados en resonancia de modos con pérdidas (lossy mode resonances, LMR). Tras un análisis exhaustivo de la situación actual, donde se describen y comparan los diferentes tipos de biosensores de fibra óptica entre sí en base a parámetros como sensibilidad, FoM, FMHW y LoD, se desarrollaron diferentes biosensores basados en LMR. Se trabajó con tres estructuras ópticas diferentes: multimodo sin nucleo multimodo o multimode coreless multimode (MCM), fibra de 200 μm sin cladding y fibra tipo D. En ellas se generaron LMRs a través de dos técnicas de deposición de películas delgadas, oxido de estaño mediante sputtering y TiO2/PSS mediante layer by layer sefl asembly. Se demostró la viabilidad de los biosensores basados en LMR desarrollados con las diferentes estructuras de fibra óptica. Con ellos, se pudo detectar biomarcadores de importancia clínica como el biomarcador del Alzheimer proteína Tau o biomarcadores de gravedad durante la infección Covid19: las proteínas C reactiva y dímero D. Además, estas estructuras han permitido implementar optimizaciones sobre biosensores de fibra óptica como el desarrollo de biosensores reutilizables, regenerables y multiparamétricos., This thesis work focuses on the development and optimization of fiber optic biosensors based on lossy mode resonances (LMRs). Following a comprehensive analysis of the current situation, where different types of fiber optic biosensors are described and compared based on parameters such as sensitivity, FoM, FMHW, and LoD, various LMR-based biosensors were developed. Three different optical structures were employed: multimode coreless multimode (MCM), 200 μm multimode fiber, and D-shaped fiber. LMRs were generated in these structures using two thin film deposition techniques: tin oxide via sputtering and TiO2/PSS via Layer-by-Layer self-assembly. The viability of the LMR-based biosensors developed with the different fiber structures was demonstrated. These biosensors enabled the detection of clinically relevant biomarkers such as the Alzheimer's biomarker Tau protein or severity biomarkers during Covid19 infection, C-reactive protein, and D-dimer. Furthermore, these structures have allowed for the implementation of optimizations on fiber optic biosensors such as the development of reusable, regenerable, and multiparametric biosensors., Aportaciones económicas recibidas: Universidad Pública de Navarra (UPNA) a través de la beca predoctoral y proyectos como: PJUPNA1936, PJUPNA2033, patrocinio de la UPNA y del Ministerio de Ciencia e Innovación (proyectos con referencias: TEC2016-78047-R, PID2019-106231RB-I00). También proyecto concedido por el Gobierno de Navarra, 011-1365-2020-000061 Breathalyser, y financiación otorgada por la comisión Europea a través del proyecto H2020-ATTRACT-OBUS., Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011), Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa Ofiziala (ED 99/2011)

En este trabajo de tesis se muestra el estudio y diseño de sensores basados en el fenómeno de la resonancia de modos con pérdidas en configuración de guía de onda plana, lo que supone un complemento para la plataforma habitual, la fibra óptica. Sus ventajas son la simplicidad de manejo y la robustez de los dispositivos desarrollados. En este sentido, se ha diseñado, sobre la base de la deposición de óxido de cobre (CuO) como material generador de la resonancia, sensores de humedad y de respiración, y sobre la base de la deposición de óxido de tungsteno (WO3), sensores de índice de refracción y de compuestos orgánicos como el etanol, el metanol y la acetona., This thesis work shows the study and design of sensors based on the phenomenon of lossy mode resonance in a planar waveguide configuration, which is a complement to the usual platform, optical fiber. Its advantages are the simplicity of use and the robustness of the devices developed. In this sense, it has been designed, based on the deposition of copper oxide (CuO) as a resonance generating material, humidity and respiration sensors, and based on the deposition of tungsten oxide (WO3), sensors for refractive index and organic compounds such as ethanol, methanol and acetone., Fondo de investigación PID2019-106231RB-I00 de la Agencia Estatal de Investigación española (AEI). Beca de investigación predoctoral de la Universidad Pública de Navarra., Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011), Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011)

Double-clad fibers where the second cladding has a lower refractive index than the first cladding, prove to be ideal structures for potentiating and tuning the sensitivity in long-period fiber gratings (LPFGs) operating in mode transition. When a thin film is deposited on the optical fiber, the second cladding performs acts as a barrier that initially prevents the transition to guidance in the thin film of one of the modes guided in the first cladding. Finally, the transition to guidance occurs with a sensitivity increase, in analogy to the tunnel effect observed in semiconductors. This improvement has been demonstrated both as a function of the thin film thickness and the surrounding medium refractive index, with enhancement factors of 4 and 2, respectively. This idea reinforces the performance of LPFGs, adding a new degree of freedom to the mode transition and the dispersion turning point phenomena. Moreover, the control of the variation of the effective index of cladding modes could be applied in other structures, such as tilted-fiber gratings or evanescent wave sensors., We acknowledge the support of the Agencia Estatal de Investigación of Spain (PID2019-106231RB-I00); the Spanish Ministry of Universities (FPU18/03087 grant); European Commission (H2020 - MSCA-RISE-2019-872049); Generalitat Valenciana (IDIFEDER/2020/064,PROMETEO/2019/048), and the Instituto Tecnologico Metropolitano, project P21101.

The development of resonance phenomena-based optical biosensors has gained relevance in recent years due to the excellent optical fiber properties and progress in the research on materials and techniques that allow resonance generation. However, for lossy mode resonance (LMR)-based sensors, the optical fiber presents disadvantages, such as the need for splicing the sensor head and the complex polarization control. To avoid these issues, planar waveguides such as coverslips are easier to handle, cost-effective, and more robust structures. In this work, a microfluidic LMR-based planar waveguide platform was proposed, and its use for biosensing applications was evaluated by detecting anti-immunoglobulin G (anti-IgG). In order to generate the wavelength resonance, the sensor surface was coated with a titanium dioxide (TiO2) thin-film. IgG antibodies were immobilized by covalent binding, and the detection assay was carried out by injecting anti-IgG in PBS buffer solutions from 5 to 20 μg/mL. The LMR wavelength shifted to higher values when increasing the analyte concentration, which means that the proposed system was able to detect the IgG/anti-IgG binding. The calibration curve was built from the experimental data obtained in three repetitions of the assay. In this way, a prototype of an LMR-based biosensing microfluidic platform developed on planar substrates was obtained for the first time, This research was funded by the Spanish Agencia Estatal de Investigacion (AEI) with reference PID2019-106231RB-I00 and also by the Public University of Navarra, with the project BIOFOCEL (ref. PJUPNA2033) and a pre-doctoral research grant.

In this work a new multiparameter sensor platform based on lossy mode resonances is presented. The structure consists of a soda-lime optical slab waveguide butt-coupled to multimode optical fibers. A variable thickness thin-film is deposited to generate multiple independent resonances on the same waveguide, which can be monitored using a single spectrometer. In order to show the potentiality of the structure, a broad resonance was selectively narrowed by etching sections of the LMR producer thin film. The spectral width is progressively reduced, allowing to selectively isolate independent resonances, which opens the path for multiple LMR generation in the same spectra in a multiparameter sensing platform. The experimental results were corroborated with a theoretical analysis based on the finite difference method (FDM). As a proof of concept, two refractometers on the same waveguide were fabricated and tested using PDMS cells. This platform can be easily miniaturized in order to integrate multiple sensors at low cost, what can be of interest for the development of multi-analyte biosensors probes. IEEE, This work was supported in part by the Spanish Ministry of Economy and Competitiveness under Grant PID2019-106070RB-I00 and Grant PID2019-106231RB-I00.

This work presents the implementation of a thermo-refractometer, which integrates the measurement of both refractive index and temperature in a single optical fiber structure. To this purpose, a lossy mode resonance (LMR)-based refractometer is obtained by means of the deposition of a titanium dioxide (TiO2) thin film onto a side-polished (D-shaped) single mode fiber. Measurement and subsequent temperature compensation are achieved by means of a fiber Bragg grating (FBG) inscribed in the core of the D-shaped region. The LMR wavelength shift is monitored in transmission while the FBG (FBG peak at 1533 nm) displacement is observed in reflection. The LMR is sensitive to both the surrounding refractive index (SRI), with a sensitivity of 3725.2 nm/RIU in the 1.3324-1.3479 range, and the temperature (- 0.186 nm/°C); while the FBG is only affected by the temperature (32.6 pm/°C in the 25°C - 45°C range). With these values, it is possible to recover the SRI and temperature variations from the wavelength shifts of the LMR and the FBG, constituting a thermo-refractometer, where it is suppressed the effect of the temperature over the refractometer operation, which could cause errors in the fourth or even third decimal of the measured SRI value., Ministerio de Ciencia, Innovación y Universidades (FPU18/03087, PID2019-106231RB-I00 TEC); Universidade Tecnológica Federal do Paraná; Conselho Nacional de Desenvolvimento Científico e Tecnológico.

Multiple mode resonance shifts in tilted fiber Bragg gratings (TFBGs) are used to simultaneously measure the thickness and the refractive index of TiO2 thin films formed by Atomic Layer Deposition (ALD) on optical fibers. This is achieved by comparing the experimental wavelength shifts of 8 TFBG resonances during the deposition process with simulated shifts from a range of thicknesses (T) and values of the real part of the refractive index (n). The minimization of an error function computed for each (n, T) pair then provides a solution for the thickness and refractive index of the deposited film and, a posteriori, to verify the deposition rate throughout the process from the time evolution of the wavelength shift data. Validations of the results were carried out with a conventional ellipsometer on flat witness samples deposited simultaneously with the fiber and with scanning electron measurements on cut pieces of the fiber itself. The final values obtained by the TFBG (n = 2.25, final thickness of 185 nm) were both within 4% of the validation measurements. This approach provides a method to measure the formation of nanoscale dielectric coatings on fibers in situ for applications that require precise thicknesses and refractive indices, such as the optical fiber sensor field. Furthermore, the TFBG can also be used as a process monitor for deposition on other substrates for deposition methods that produce uniform coatings on dissimilar shaped substrates, such as ALD., The authors would like to acknowledge the Spanish Ministry of Universities
the support of this work through 260 FPU18/03087 grant (Formación de
Profesorado Universitario) and the Spanish Ministry of Science and Innovation
261 PID2019-106231RB-I00 TEC Research project, as well as NSERC
under Grant RGPIN-2019-06255.

A 5-layer stack composed of TiO2 and Al2O3, two materials with a high refractive index contrast, was deposited on a D-shaped fiber to generate Bloch surface wave resonances with an improved figure of merit., This work was supported by the National Science Centre (NCN), Poland, OPUS program, project No.
2019/35/B/ST7/04388, and the National Centre for Research and Development (NCBiR), Poland, as a part of
TECHMATSTRATEG-III/0042/2019 project. Support received from Mr. Tomasz Gabler within ALD experiments is
also acknowledged. The authors also acknowledge the support of the Spanish Ministerio de Ciencia e Innovación
(PID2019-106231RB-I00 and PDI2019-104276RB-I00), the FPI program grant, the Universidad Nacional de
Colombia–Sede Medellín through the Postdoctoral Internship Program (Hermes code 53395) and the Instituto
Tecnológico Metropolitano (project P20212).

Ethylene monitoring has long been a method of controlling the ripening of climacteric fruits, but it turns out that this gas is an important biomarker in biomedical applications. This work presents an optical gas sensor based on the lossy mode resonance (LMR) effect for ethylene detection in planar waveguide configuration. Two different approaches have been explored: one in the visible (VIS) spectral region and the second one in the mid infrared (MIR) region. Optical resonances have been achieved, in all cases, by means of sputtered tin oxide thin films. Response and recovery times were 54 and 246 s, respectively, for the sensor with the resonance in the VIS region, while the device operating in the MIR obtained response and recovery times of 19 and 47 s, respectively. The sensitivity during ethylene detection varied from 93.8 to 187.5 pm/ppm with the devices working in the VIS and MIR regions, respectively. According to the calibration curve, devices show an ethylene limit of detection (LOD) of 4.0058 and 0.6532 ppm in the VIS and MIR spectral regions, respectively, which finds applications in climacteric fruit ripening assessment as well as hemodialysis control. Cross sensitivity with humidity was also characterized for both devices., This work was supported by Agencia Estatal de Investigación under Grant PID2019-
106231RB-I00 and Grant PID2022-137437OB-I00 and in part by the Institute Smart Cities
and Public University of Navarra Ph.D. Student grants.

This work aims to provide a brief overview of the latest trends in the domain of optical biosensors., Ministerio de Ciencia, Innovación y Universidades (FPU18/03087) and Agencia Estatal de Investigación (PID2019-106231RB-I00 TEC)

Coverslips deposited with a metallic oxide can be employed for generating lossy mode resonances by lateral incidence of light on the coverslip. Here it is demonstrated that with copper oxide the fading observed with other materials in the near infrared (NIR) wavelength range is avoided and LMRs can be obtained in a broadband range from 400 to 1700 nm, which permitted to observe the better performance in the NIR region compared to the visible region: the sensitivity to humidity is improved by more than a factor of two. However, copper oxide is not adequate for sensing humidity. The sensitivity of the device was optimized initially with a tin oxide coating and later with an additional layer of agarose, specifically adequate for the detection of humidity. The best performance was obtained with an agarose concentration 1% w/v, which permitted to observe a 10-fold sensitivity increase compared to the same device without agarose. This opens the path towards the development of environmental, chemical or biological sensors with an optimized sensitivity to a specific parameter to detect., The authors would like to acknowledge the support of the Agencia Estatal de Investigación (AEI) del Ministerio de Ciencia, Innovación y Universidades of Spain through the research project PID2019-106231RB-I00 and the predoctoral research grant from the Public University of Navarra.

In this work, the characteristics of lossy mode resonances (LMRs) in double-clad fibers where the refractive index (RI) of the second cladding is lower than that of the first cladding are analyzed both numerically and experimentally. In the first place, the LMRs spectra obtained with a 75 nm TiO 2 thin film are simulated, and it is observed that a thicker second cladding improves the width of the resonances, making them narrower. Then, two experimental cases (no second cladding, and second cladding with thickness of 1.13 μm) are assessed, showing a good agreement with the previous simulations. Finally, an experimental refractometric study is carried out in liquids (surrounding medium refractive index in the 1.34 - 1.40 range) for both fibers, calculating the full width at 1 dB (FW 1dB ), the sensitivity, and the figure of merit (FOM). The FW 1dB is better for the LMR obtained on the fiber with second cladding while the sensitivity is slightly greater for the fiber without second cladding. In the case of the FOM, it is higher for the double-clad fiber as the narrowing of the resonances outweighs the lower sensitivity. These results show that the performance of LMR-based optical fiber sensors can be improved by employing double-clad fibers., This work was supported by the Spanish Ministry of Universities,
Formación de Profesorado Universitario, under Grant FPU18/03087 and in part
by the Spanish Ministry of Science and Innovation through Research Fund under
Grant PID2019-106231RB-I00 TEC.

The utilization of nanometric Graphene Oxide / Polyethyleneimine (GO/PEI) bilayers deposited onto SnO2-coated CaF2 planar waveguides significantly enhances the sensitivity of Lossy Mode Resonances (LMR) based devices for gas sensing applications. LMR generation in the mid-infrared region, which also contributed to achieve better sensitivities, was accomplished with the aid of fluorinated (CaF2) planar waveguides. LMR wavelength shift was studied as a function of the number of GO/PEI bilayers. In the particular case of 10 bilayers of GO/PEI, the sensitivity of the device to 1-butanol was 70.4 pm/ppm, which increased by a factor of 5 compared to the device without GO/PEI bilayers. The GO/PEI sensor was also sensitive to other alcohols, like 2-propanol, but it showed negligible sensitivity to other gases, such as CO2, NH3 or C2H2. The cross sensitivity with temperature was tested at temperatures of 20, 100 and 180 ºC during water vapor measurement (1723 ppm), showing that the sensor performance was not affected by the temperature fluctuations., This work was supported by Agencia Estatal de Investigación ( PID2019-106231RB-I00 ), Institute Smart Cities and Public University of Navarra Ph.D. Student grants. SM-E would like to express her gratitude for the Fellowship supported by the Royal Academy of Engineering under the Leverhulme Trust Research Fellowships scheme (LTRF2021\17130).

The results presented here show for the first time the experimental demonstration of the fabrication of lossy mode resonance (LMR) devices based on perovskite coatings deposited on planar waveguides. Perovskite thin films have been obtained by means of the spin coating technique and their presence was confirmed by ellipsometry, scanning electron microscopy, and X-ray diffraction testing. The LMRs can be generated in a wide wavelength range and the experimental results agree with the theoretical simulations. Overall, this study highlights the potential of perovskite thin films for the development of novel LMR-based devices that can be used for environmental monitoring, industrial sensing, and gas detection, among other applications., The authors would like to acknowledge the partial support to Agencia Estatal de Investigación PID2019-106231RB-I00 research project, Universidad Rey Juan Carlos with research project “Células fotovoltaicas de tercera generación basadas en semiconductores orgánicos avanzados perovskitas híbridas en estructuras multiunión” (reference M2607), and the pre-doctoral research grant of the Public University of Navarra.

A planar waveguide consisting of a coverslip for a microscope glass slide was deposited in one of its two faces with two materials: silver and indium tin oxide (ITO). The incidence of light by the edge of the coverslip permitted the generation of both surface plasmon and lossy mode resonances (SPRs and LMRs) in the same transmission spectrum with a single optical source and detector. This proves the ability of this optical platform to be used as a benchmark for comparing different optical phenomena generated by both metal and dielectric materials, which can be used to progress in the assessment of different sensing technologies. Here the SPR and the LMR were compared in terms of sensitivity to refractive index and figure of merit (FoM), at the same time it was demonstrated that both resonances can operate independently when silver and ITO coated regions are surrounded by different refractive index liquids. The results were supported with numerical results that confirm the experimental ones., The authors would like to acknowledge the partial support to the Agencia Estatal de Investigacion (AEI) PID2019-106070RB-I00 and PID2019-106231RB-I00 research funds, and the predoctoral research grants of the Public University of Navarra.

A Bloch surface wave (BSW) resonance configuration is introduced for biosensing with an ultra-high figure of merit (FOM). The BSW excitation is realized through the evanescent field of the core-guided fundamental mode of a side-polished photonic crystal fiber (PCF). By taking advantage of the air hole periodic microstructure of the PCF cladding, the BSW platform can be achieved with only a single high refractive index dielectric layer on its flat surface. The dielectric layer deposited on the polished surface of the PCF modifies the local effective refractive index, allowing direct manipulation of the BSWs, whereby the resonance wavelength of the surface wave can be adjusted by choosing the material and thickness of this layer. Here, we numerically investigate Bloch-like surface wave (BLSW) resonance conditions around telecom wavelengths for silicon, titanium dioxide, copper monoxide, and aluminum oxide termination layers. The BLSW excitation platform materials have low loss, which results in higher surface field enhancements and narrower resonances, which are advantageous properties for the sensors. The obtained results open new avenues for the application of optical surface waves in biosensing with high FOM. Furthermore, these results show a much higher figure of merit (FOM) than traditional approaches, allowing for increased sensitivity and accuracy., This work is partially funded by the Instituto Tecnológico Metropolitano, project P20212, the Universidad Nacional de Colombia, Facultad de Ciencias de la sede Medellín, (Hermes codes 53395, 56330) and the Spanish National Research Agency (AEI) through the project with reference PID2019-106231RB-I00.

Multi-parameter detection is key in the domain of sensors. Here it is demonstrated that an indium tin oxide (ITO) nanocoating can be used to generate multiple lossy mode resonances (LMRs) in the optical spectrum. To achieve this, a nanocoating with a gradient in thickness is generated on the surface of a planar waveguide, permitting broadening of the LMR because the position of an LMR in the optical spectrum is directly related to the nanocoating thickness. The nanocoating with a gradient in thickness contributes multiple LMRs, each one centred at a different wavelength. With a further etching or deposition using a mask, a pattern of deposited and non-deposited regions can be created, resulting in isolation of the LMRs by preventing LMR overlap. This enables tracking of each central wavelength separately, which can be tuned through control of the gradient or nanocoating pattern. The array of LMR-based sensors is a photonics analogue to the interdigital concept in electronics, enabling multiple resonances to be used for multiparameter sensing., The authors would like to acknowledge the partial support to the Spanish Ministry of Economy and Competitiveness TEC2016-79367-C2-2-R and PID2019-106231RB-I00 research fund, the STARDUST project (European Commission) and the pre-doctoral research grants of the Public University of Navarra.

Lossy mode resonance (LMR) based refractometers obtained by means of copper oxide thin-films fabricated onto side-polished (D-shaped) are presented in this work. The high refractive index of copper oxide combined with the propagation mode isolation capabilities of D-shaped fibers allows for the observation of narrow (30 nm) and high sensitive (10,336 nm per refractive index unit) LMRs, which could enable to improve the performance of LMR-based refractometers as well as provide an alternative label-free sensing platform for LMR-based sensors., The authors would like to acknowledge the support from the Spanish Agencia Estatal de Investigación (AEI) (PID2019-106231RB-I00) and the Public University of Navarra (PJUPNA26). A. O. C. would also like to thank the Spanish Ministry of Universities (FPU15/05663).

Copper oxide (CuO) allows the generation of lossy mode resonance (LMR) in a wide wavelength range of the optical spectrum, both in the visible and the near-infrared (NIR). For this, it is necessary to use a configuration based on the lateral incidence of light on the edge of a planar waveguide structure. On the other hand, the use of additional coatings of tin oxide (SnO2) and agarose allows an increase in the sensitivity of the sensor, in response to the breathing monitoring. The sensors were characterized, both in intensity and wavelength. In both cases their behavior depends on the position of the LMR in the optical spectrum. Therefore, it is convenient to extract the design rules that allow an optimal behavior of the sensor. In this sense, sensors located in the NIR presented a better behavior in terms of sensitivity and quality of the signal. In addition, the devices were tested in different conditions: repetitive tests at different distances, oral and nasal breathing, and breathing after doing physical exercise., The authors would to acknowledge the partial support to the Agencia Estatal de Investigacion (AEI) from the Spanish Ministry of Economy and Competitiveness (PID2019-106231RB-I00 and PID2019-106070RB-I00 research funds) and the predoctoral research grant of the Public University of Navarra.

A first approach study for the classification of alfalfa (medicago sativa) quality has been performed by means of VIS-NIR optical fiber reflection spectroscopy. Reflection spectral data has been obtained from alfalfa samples comprising six different qualities. Obtained data has been classified and organized to feed supervised self-learning algorithms. Neural networks have been used in order to differentiate the quality level of the samples. Obtained results permit to validate the proposed approach with 72% of the samples properly classified. In addition, proposed solution was implemented in a low cost automated detection prototype suitable to be used by non-qualified operators. Obtained equipment consist of a first step towards its utilization in quality monitoring and classification of many other products in the agri-food field., This work was supported by the Spanish Ministry through FPU18/03087 and PID2019-106231RB-I00 grants, Government of Navarra 0011-1365-2021-000065 and 0011-1408-2021-000007 grants and UPNA-ISC PhD grant.

Tungsten oxide (WO3) thin-films fabricated on glass slides have been proven to generate lossy mode resonances (LMRs) in the visible region. Obtained devices were characterized in transmission by lateral incidence of light on the edge of glass slides. Resonances at both TE and TM polarizations were analyzed for different thicknesses and in different deposition conditions. Moreover, it was successfully proved that WO3 coated glass slides present a high sensitivity to refractive index, which opens the path to the application of this structure in the domain of optical sensors., This work was supported in part by the Spanish Agencia Estatal de Investigación (AEI) through project PID2019-106231RB-I00 and by Italian Ministry of University and Research (MIUR) through the University Research Project 2017 (prot. RG11715C8213BD81).

DNA is becoming increasingly important in the domain of optical fiber sensors, either as a tool for biosensing, or as a target to detect. In this review the main contributions of the last years are presented both in the domain of wavelength and intensity based configurations. This review comprises the use of natural single strand DNA (ssDNA) sequences as receptors for the detection of ssDNA sequences through hybridization, synthetic nucleic acids receptors for detection of complementary ssDNA sequences, and sensors based on natural and synthetic ssDNA receptors used for the detection of non-DNA targets. Parameters such as sensitivity, detection range and limit of detection are analyzed and discussed in detail to the purpose of comparing the different technologies and knowing the future lines to follow in the domain of fiber optic DNA-based sensors., This work was supported in part by the Spanish Agencia Estatal de Investigación (AEI) under Grant PID2019-106231RB-I00, in part by the Public University of Navarra under Grant PJUPNA26, in part by the Ph.D. Research Grants, and in part by the ATTRACT Call financed by the European Union’s Horizon 2020 Research and Innovation Program under Grant 777222.

With the goal of ultimate control over the light propagation, photonic crystals currently represent the primary building blocks for novel nanophotonic devices. Bloch surface waves (BSWs) in periodic dielectric multilayer structures with a surface defect is a well-known phenomenon, which implies new opportunities for controlling the light propagation and has many applications in the physical and biological science. However, most of the reported structures based on BSWs require depositing a large number of alternating layers or exploiting a large refractive index (RI) contrast between the materials constituting the multilayer structure, thereby increasing the complexity and costs of manufacturing. The combination of fiber–optic-based platforms with nanotechnology is opening the opportunity for the development of high-performance photonic devices that enhance the light-matter interaction in a strong way compared to other optical platforms. Here, we report a BSW-supporting platform that uses geometrically modified commercial optical fibers such as D-shaped optical fibers, where a few-layer structure is deposited on its flat surface using metal oxides with a moderate difference in RI. In this novel fiber optic platform, BSWs are excited through the evanescent field of the core-guided fundamental mode, which indicates that the structure proposed here can be used as a sensing probe, along with other intrinsic properties of fiber optic sensors, as lightness, multiplexing capacity and easiness of integration in an optical network. As a demonstration, fiber optic BSW excitation is shown to be suitable for measuring RI variations. The designed structure is easy to manufacture and could be adapted to a wide range of applications in the fields of telecommunications, environment, health, and material characterization., Fundación para la Promoción de la Investigación y la Tecnología-Banco de la República of Colombia (Contract 202103); Universidad Nacional de Colombia (Hermes code 46509); Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (TEC2016-78047-R and PID2019-106231RB-I00).
E.G.V. acknowledges the support of COLCIENCIAS through the Doctoral Scholarship program.

There exists an increasing interest in monitoring low concentrations of biochemical species, as they allow the early-stage detection of illnesses or the monitoring of the environment quality. Thus, both companies and research groups are focused on the development of accurate, fast and highly sensitive biosensors. Optical fiber sensors have been widely employed for these purposes because they provide several advantages for their use in point-of-care and real-time applications. In particular, this review is focused on optical fiber biosensors based on luminescence and absorption. Apart from the key parameters that determine the performance of a sensor (limit of detection, sensibility, cross-sensibility, etc.), other features are analyzed, such as the optical fiber dimensions, the sensing set ups and the fiber functionalization. The aim of this review is to have a comprehensive insight of the different aspects that must be taken into account when working with this kind of sensors., This research was funded by the Spanish AGENCIA ESTATAL DE INVESTIGACIÓN (AEI), through the project with reference PID2019-106231RB-I00—ESPADA and also by the Regional Government of Navarra, through the project with reference 0011-1365-2020-000061–BREATHALYSER (FEDER).

The use of planar waveguides has recently shown great success in the field of optical sensors based on the Lossy Mode Resonance (LMR) phenomenon. The properties of Graphene Oxide (GO) have been widely exploited in various sectors of science and technology, with promising results for gas sensing applications. This work combines both, the LMR-based sensing technology on planar waveguides and the use of a GO thin film as a sensitive coating, to monitor ethanol, water, and acetone. Experimental results on the fabrication and performance of the sensor are presented. The obtained results showed a sensitivity of 3.1, 2.0, and 0.6 pm/ppm for ethanol, water, and acetone respectively, with a linearity factor R2 &gt; 0.95 in all cases., This work was supported by Agencia Estatal de Investigación (PID2019-106231RB-I00), Institute of Smart Cities and Public University of Navarra PhD Student grants, and in part by the European Union Horizon 2020 Research and Innovation Programme (Stardust-Holistic and Integrated Urban Model for Smart Cities) under Grant 774094. SM-E would like to express her gratitude for the Fellowship supported by the Royal Academy of Engineering under the Leverhulme Trust Research Fellowships scheme (LTRF2021\17130).

Two different thin film designs with a grating pattern are simulated on a soda lime coverslip, which acts as optical waveguide, with the purpose of generating both a lossy mode resonance (LMR) in transmission and reflection bands. This way both phenomena can be made sensitive to different parameters, leading to a multi-sensing device. The first design consists of a grating patterned in a SnO2 thin film deposited on the coverslip. The performance of the device in both transmission and reflection is numerically studied in air for different values of the grating pitch. Small grating pitches (in the order of the µm) are more suitable for generating the reflection bands while larger values (500 µm or more) are required to produce the LMR, when the reflection bands are no longer visible. Due to the inability to obtain both phenomena with this design, a second design is assessed, where the grating is combined with a section of constant thickness. In this case the desired response is obtained, which opens the path to use this device for multi-sensing applications, measuring several parameters at the same time., This research was funded by the Spanish Ministry of Universities (FPU18/03087 grant), and the Spanish Ministry of Economy and Competitiveness (PID2019-106231RB-I00 research fund).