BUSCADOR RECOLECTA

This work presents an optical sensor for ultraviolet radiation (UV) detection, based on the combined effects of
Lossy Mode Resonance (LMR) in the mid infrared (MIR) spectral region and the photoisomerization of a polymeric dye coating. LMR was obtained by means of a sputtered SnO2 thin film on a tetrafluoroethylene-perfluoro
(or alkoxy Vinyl Ether, PFA) substrate, along with a photo sensitive coating based on poly R-478. Obtained
devices shown response and recovery times of 12 and 43 s, respectively, for an UV excitation of 71 mW at 365
nm. Sensitivity as a function of the excitation wavelength was studied with the highest value of 26 nm/mW
obtained at 280 nm. For this excitation wavelength, the limit of detection (LoD) obtained was 0.024 mW. Four
different excitation wavelengths were used to cover all UV regions (280, 310, 365 and 395 nm). All measurements were performed at room temperature and humidity (25 ¿C ± 1 ¿C and 13% R.H. ± 2% R.H. respectively).
As far as we know, it is the first time that the LMR effect has been recognized in combination with a photoisomerization process., This work was supported by Agencia Estatal de Investigación (PID2022-137437OB-I00), Institute Smart Cities and Public University of Navarra Ph.D. student grant.

From an optical perspective, depending on the relationship between the real (n) and imaginary (k) parts of its refractive index, three broad categories of materials can be distinguished: metals (k ¿ n), dielectrics (n ¿ k), and materials in which n ¿ k (termed here excitonic materials). The modes and optical resonances that appear in a thin film bounded by two dielectrics with similar refractive index, what we call here a double interface structure, have been widely studied in the case of metals, but not for dielectrics, or materials with n ¿ k. In this work, we propose a new approach, based on employing the phase matching condition to correlate the resonances that appear in the wavelength versus incident angle color maps of the reflected power with the modal analysis of the cross section of the structure. This analysis is performed, using an attenuated total reflection (ATR) setup, for thin film materials that belong to each of the mentioned categories: a metal (gold, Au), a dielectric (titanium dioxide, TiO2), and a material with n ¿ k (chromium, Cr). The theoretical analysis is supported with experimental results. It is demonstrated that this method enables to identify any resonance at any wavelength or incident angle, being valid for all three types of materials. Therefore, it is considered the suggested approach will help the research in these materials and in the double interface structure in the optics and photonics field., This work was supported by Agencia Estatal de Investigación (PID2022-137437OB-I00).

Esta tesis ha contribuido al desarrollo de biosensores basados en Resonancias de Modos con Pérdidas (Lossy Mode Resonance, LMR) al proponer la transición en el uso de fibra óptica a sustratos planos, destacando su simplicidad, bajo coste y gran versatilidad. Se presenta el desarrollo de una plataforma microfluídica basada en LMR en guía de onda plana y su aplicación en la detección de biomarcadores como anti-IgG, gliadina, antigliadina, VEGF e IL-6. Se comprueba el desempeño de los biosensores al utilizar tres estructuras de nanorecubrimientos—TiO₂, SiO₂+TiO₂ y Au+TiO₂—las cuales han probado su utilidad en la generación de LMRs y en la mejora de sus propiedades. Se emplean nanopartículas de oro, por primera vez, para amplificar la señal de los LMRs, logrando una mejora significativa en la sensibilidad. Los resultados obtenidos demuestran la versatilidad y eficacia del sistema propuesto y confirman que la plataforma microfluídica y el diseño basado en sustratos planos constituyen una base sólida para el desarrollo de dispositivos LMR adaptables a una amplia variedad de aplicaciones en áreas como la medicina, la biotecnología o la industria alimentaria., This thesis advances the field of Lossy Mode Resonance (LMR) biosensors by transitioning from fiber optic substrates to planar waveguides, emphasizing their simplicity, cost-effectiveness, and versatility. It presents the development of an LMR-based microfluidic platform developed in planar waveguide and its application in detecting critical biomarkers such as anti-IgG, gliadin, antigliadin, VEGF, and IL-6. The performance of the biosensors is assessed when using three nanocoating structures—TiO₂, SiO₂+TiO₂, and Au+TiO₂—selected for their proven utility to generate LMRs and to improve their features. Notably, gold nanoparticles are employed for the first time to enhance signal in LMR sensors, significantly improving the sensitivity. The results obtained demonstrate the versatility and effectiveness of the proposed system, confirming that the microfluidic platform and the planar substrate-based design provide a robust foundation for the development of LMR devices adaptable to a wide range of applications in fields such as medicine, biotechnology, and food industry., El desarrollo de este trabajo ha sido posible gracias a las aportaciones económicas recibidas de la Universidad Pública de Navarra (UPNA) a través de la beca predoctoral y del proyecto BIOFOCEL (ref. PJUPNA2033), así como a la financiación de la Agencia Estatal de Investigación (AEI) de España, con las referencias PID2019-106231RB-I00 y PID2022-137437OB-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 Ofiziala (ED 99/2011)

The incorporation of organic groups into sol-gel silica materials is known to have a noticeable impact on the properties and structure of the resulting xerogels due to the combination of the properties inherent to the organic fragments (functionality and flexibility) with the mechanical and structural stability of the inorganic matrix. However, the reduction of the inorganic content in the materials could be detrimental to their thermal stability properties, limiting the range of their potential applications. Therefore, this work aims to evaluate the thermal stability of hybrid inorganic-organic silica xerogels prepared from mixtures of tetraethoxysilane and organochlorinated triethoxysilane precursors. To this end, a series of four materials with a molar percentage of organochlorinated precursor fixed at 10%, but differing in the type of organic group (chloroalkyls varying in the alkyl-chain length and chlorophenyl), has been selected as model case study. The gases and vapors released during the thermal decomposition of the samples under N2 atmosphere have been analyzed and their components determined and quantified using a thermogravimetric analyzer coupled to a Fourier-transform infrared spectrophotometer and to a gas chromatography-mass spectrometry unit. These analyses have allowed to identify up to three different thermal events for the pyrolysis of the organochlorinated xerogel materials and to elucidate the reaction pathways associated with such processes. These mechanisms have been found to be strongly dependent on the specific nature of the organic group., This work was supported by the projects PID2020-113558RB-C42, PID2022-137437OB-I00 and PID2022-142169OB-I00, financed by MCIN/AEI/10.13039/501100011033

This letter presents the fabrication and characterization of an ammonia (NH 3) gas optical sensor based on lossy mode resonances (LMRs). A chromium (III) oxide (Cr 2 O 3) thin film deposited onto a planar waveguide was used as LMR supporting coating. The obtained LMR shows a maximum attenuation wavelength or resonance wavelength centered at 673 nm. The optical properties of the coating can be modified as a function of the presence and concentration of NH 3 in the external medium. Consequently, the refractive index of the Cr 2 O 3 thin film will change, producing a red-shift of the resonance wavelength. Obtained devices were tested for different concentrations of NH 3 as well as repetitive cycles. Concentrations as low as 10 ppbv of NH 3 were detected at room temperature. Machine learning regression models were used to mitigate the cross-sensitivity of the device under temperature and humidity fluctuations., This work was supported in part by the Spanish Ministry of Science and Innovation under Grant FPI PRE2020-091797, in part by the Spanish Agencia Estatal de Investigacion under Grant PID2022-137437OB-I00, and in part by the European Union's Horizon 2020 Research and Innovation Programme (Stardust-Holistic and Integrated Urban Model for Smart Cities) under Grant 774094.

Surface plasmon resonance (SPR) and lossy mode resonance (LMR) are prominent sensing mechanisms utilized across various fields. The Kretschmann configuration is commonly employed for SPR, while LMR is favored in planar waveguides or optical fibers due to high incidence angles. Recently, hyperbolic mode resonance (HMR) has emerged as a hybrid approach, combining metallic and dielectric thin films. This study explores the impact of incidence angle on HMR using the Kretschmann configuration. Four samples with varying gold (Au) and tin dioxide (SnO2) layer thicknesses were fabricated and characterized using Atomic Force Microscopy (AFM). Experimental setups employed the Kretschmann configuration for reflectance spectrum analysis. Results indicate enhanced sensitivity and figure of merit (FoM) with an additional SnO2 layer compared to the case without SnO2. Particularly with a 36 nm Au thickness the sensitivity doubles and the FoM improves by 16 %. Numerical simulations validate these findings, confirming the optimized performance of HMR for specific layer thicknesses and incidence angles., This work was supported in part by the Agencia Estatal de Investigación (AEI) from the Spanish Ministry of Economy and Competitiveness (PID2022-137437OB-I00) research fund and by the pre-doctoral research grant of the Public University of Navarra.

Lossy mode resonance (LMR)-based sensors have experienced an important development in the last decade. Among the different domains in which LMR-based sensors have been used, biosensing is one of the fields that has attracted more interest in recent years. Here, LMR properties and some biosensing concepts are reviewed in the first place. Then, the progress of LMR-based biosensors is described, starting with cladding-removed multimode fibers (CRMMF), and evolving towards the employment of D-shaped single mode fibers, which have led to better biosensors in terms of performance and limit of detection (LOD). More recent advances, such as the development of biosensors that combine the optical and electrochemical domains, or the introduction of planar waveguides as the biosensor substrate, are also discussed. In all the cases, examples of biosensors are included, indicating the detected biomarker, biofunctionalization protocol, dynamic range, LOD, and specificity assays. Finally, some conclusions about LMR-based biosensors are presented, as well as future perspectives and some ideas to advance in this field., The authors would like to acknowledge the Spanish Ministry of Universities the support of this work through FPU18/03087 grant (Formación de Profesorado Universitario) and the Spanish Ministry of Science and Innovation PID2022-137437OB-I00 Research project.

In this research article, we present a comprehensive investigation into the integration of dielectric and metallic layers on optical waveguides, specifically targeting sensing applications. By utilizing a single bilayer of metal and dielectric on a planar waveguide that meets the conditions of a hyperbolic metamaterial, we significantly enhance the visibility of lossy mode resonances generated with a single dielectric layer, in what can be considered as a hyperbolic mode resonance (HMR), without compromising sensitivity. This improvement leads to an enhanced figure of merit and a reduction of the signal-to-noise ratio.
Real-time evolution of spectra during the dielectric layer deposition allows us to establish a map of the multiple phenomena involved, such as surface plasmon resonance, lossy mode resonance, and mode transition. Combining these phenomena in a single structure leads to an unprecedented enhancement in sensing capabilities, demonstrating the potential of dielectric-metallic layer integration on optical waveguides for advanced sensing applications. Moreover, the optimized sensing performance offers promising opportunities for on-chip sensing devices and various applications in biomedicine, environmental monitoring, and chemical analysis., The authors acknowledge the support of the Agencia Estatal de Investigación of Spain (PID2022-137437OB-I00); and the pre-doctoral research grant of the Public University of Navarra.

The current work describes and compares the performance of hyperbolic mode resonance (HMR)-based sensors for the detection of acetone at parts per billion (ppb) concentrations using ensemble machine learning (EML) techniques. A pair of HMR based-sensors with resonances located in the visible (VIS) and mid infrared (MIR) regions were obtained in order to train a set of ensemble machine learning models. The response of the detection system formed by both devices in the VIS and MIR regions, with the help of the EML system, allowed the limit of detection (LoD) of the sensors to be reduced by an order of magnitude. It is the first time that HMR-based sensors are shown in practical applications, at the same time that their performance is improved using EML techniques. This opens new avenues for the use of this type of HMR-based sensors for the detection of other substances, in addition to improving the performance of any optoelectronic sensor using EML techniques., This work was supported by Agencia Estatal de Investigación (PID2022-137437OB-I00 and PDC2023-145831-I00), Institute Smart Cities and Public University of Navarra Ph.D. student grant, International Mobility Scholarship of the Navarra Government, and the Radboud University.

Lossy mode resonance (LMR) is a phenomenon that is observed in the optical spectrum when a mode that progresses through a waveguide starts to be guided in a thin film deposited on this waveguide under certain conditions, mainly related to materials and angles of incidence. An important property that LMRs have is that they can be guided into the thin film with both magnetic (TM) and electrical (TE) polarized light, unlike the other two main types of optical resonances with the same modus operandi that complete this trilogy, surface plasmon resonances (SPRs) and surface exciton plasmon resonances (SEPR). Regarding the potential materials that make up thin films, they include dielectrics suchs as metal oxides such as titanium dioxide (TiO2), zinc oxide (ZnO), tin oxide (SnO2) or polymers. In all cases it must be fulfilled that the real part of the refractive index must be greater than its imaginary part, unlike also the SPR and SEPR. As for the angles of incidence, they must be close to 90º, which explains the success of deposition of thin films around an optical fiber to obtain sensors based on LMR, although interesting results have recently been obtained using planar waveguides. This work will present the main milestones obtained during more than a decade using LMR-based sensors for the detection of multiple parameters. Among these interesting aspects, we can mention the sensitivity records achieved, hybridization with other sensing technologies or the possibility of multiplexing multiple sensors on the same substrate, just to mention a few., Work supported by the Agencia Estatal de Investigación PID2022-137437OB-I00 research fund.

Maintaining both high sensitivity and large figure of merit (FoM) is crucial in regard to the performance of optical devices, particularly when they are intended for use as biosensors with extremely low limit of detection (LoD). Here, a stack of nano-assembled layers in the form of 1D photonic crystal, deposited on D-shaped single-mode fibers, is created to meet these criteria, resulting in the generation of Bloch surface wave resonances. The increase in the contrast between high and low refractive index (RI) nano-layers, along with the reduction of losses, enables not only to achieve high sensitivity, but also a narrowed resonance bandwidth, leading to a significant enhancement in the FoM. Preliminary testing for bulk RI sensitivity is carried out, and the effect of an additional nano-layer that mimics a biological layer where binding interactions occur is also considered. Finally, the biosensing capability is assessed by detecting immunoglobulin G in serum at very low concentrations, and a record LoD of 70 aM is achieved. An optical fiber biosensor that is capable of attaining extraordinarily low LoD in the attomolar range is not only a remarkable technical outcome, but can also be envisaged as a powerful tool for early diagnosis of diseases., This research was funded in Spain by Agencia Estatal de Investigacion (PID2022-137437OB-I00) and Public University of Navarra predoctoral research grants. This work was partially funded by the Instituto Tecnológico Metropolitano, project P23210, the Universidad Nacional de Colombia, Facultad de Ciencias de la sede Medellín (Hermes code 56330). E.G.V. acknowledges the support of Minciencias through the Doctoral Scholarship program. This study was carried out within the 'Fiber optics sensors as a platform for cancer diagnosis and in vitro model testing' project - funded by European Union - Next Generation EU within the PRIN 2022 PNRR (P2022Y4TP5) program (D.D.1409 del 14/09/2022 Ministero dell'Università e della Ricerca). This manuscript reflects only the authors' views and opinions and the Ministry cannot be considered responsible for them. Financial support received from the National Science Centre (NCN), Poland, under grant No. 2019/35/B/ST7/04388 and in part by National Centre for Research and Development (NCBiR), Poland under grant No. TECHMATSTRATEG-III/0042/2019, was also acknowledged. Open Access provided by Universidad Pública de Navarra within the CRUI CARE Agreement.

This letter demonstrates the fabrication of a temperature optical sensor by printing the corresponding sensitive optical waveguide directly onto a flexible flat substrate. The printed waveguide was carried out using a coaxial needle and an electrohydrodynamic (EHD) machine. The fluorescent organic compound, rhodamine B, was used for doping the core of the printed waveguide as temperature sensible dye. The optical sensitive waveguide manufactured is compact, ensuring coupling with the input and output optical fibers. The response of the printed optical sensor was evaluated to temperature variations by measurement of both, the peak intensity and the wavelength of the fluorescence spectra. The experimental characteristic and sensitivity of the sensor were obtained., This work was supported in part by the Gobierno de Navarra under Grant PC058-059 EleSpray and in part by the Agencia Estatal de Investigación under Grant PID2022-137437OB-I00 and Grant PDC2023-145831-I00.

In this work we propose electrochemical lossy mode resonance (eLMR) as a powerful method for the detection of manganese (Mn) ions. The sensor is based on a simple planar waveguide (sodasingle bondlime glass coverslip) coated with a thin layer of indium tin oxide (ITO) to obtain an optical resonance effect. Simultaneously, the ITO layer served as the working electrode in the cathodic stripping voltammetry (CSV) of Mn. The eLMR sensor is capable of simultaneously performing electrochemical (EC) and optical measurements, specifically lossy mode resonance (LMR), to monitor the growth of the adsorbed Mn layer on the ITO electrode and the electrochemically modulated diffusion layer. For Mn2+ ions, a limit of detection (LoD) of 1.26 ppb has been demonstrated using the EC method, whereas the optical method exhibited a LoD of 67.76 ppb. The results obtained indicate significant potential for application in molecular electrochemistry and studies focused on electrified interfaces., This work was supported in part by the Agencia Estatal de Investigación (AEI) from the Spanish Ministry of Economy and Competitiveness
(PID2019-106070RB-I00 and PID2022-137437OB-I00 research
funds), by the Government of Navarre through its projects with references:
and PC058-059 EleSpray and 0011-1365-2022-000241, and by
the pre-doctoral research grant of the Public University of Navarra. The
authors also acknowledge financial support received from the National
Centre for Research and Development, Poland, grant No. TECHMATSTRATEG-
III/0042/2019, as well as the Czech Science Foundation
Agency through the project 21-05030K and the National Science Centre
(NCN), Poland, as part of the 2020/02/Y/ST8/00030 project. Open
access funding provided by Universidad Pública de Navarra.

Los sensores ópticos basados en resonancias han tenido un papel
protagónico en el desarrollo de diversas tecnologías, especialmente
aquellos basados en modos con pérdidas en los últimos quince años. Una
de sus aplicaciones con mayor auge es la detección de gases.
En esta tesis se presentan los resultados obtenidos en el desarrollo de
sensores ópticos basados en resonancias para la detección de gases. Se
aborda el estado del arte de las tecnologías de sensores basados en
resonancias, incluyendo los SPR (Surface Plasmon Resonance,
resonancia de plasmón de superficie) y LMR (Lossy Mode Resonance,
resonancia de modos con pérdidas) en la detección de gases y
compuestos volátiles orgánicos. Los esfuerzos se centran en aspectos
fundamentales como: el empleo de sustratos que permitan la fabricación
de sensores basados en resonancias LMR y HMR (Hyperbolic Mode
Resonance, resonancia de modo hiperbólico) en longitudes de onda lo
más largas posible en la región infrarroja empleando materiales como el
calcio fluorado (CaF2), y la aplicación de técnicas de inteligencia artificial
para mejorar el rendimiento de estos sensores y hacer posible la
detección de múltiples gases., Optical sensors based on resonances have played a leading role in the
development of various technologies, especially those based on lossy
modes over the past fifteen years. One of its most rapidly growing
applications is gas detection.
This thesis presents the results obtained in the development of optical
sensors based on resonances for gas detection. It addresses the state of
the art of resonance-based sensor technologies, including SPR (Surface
Plasmon Resonance) and LMR (Lossy Mode Resonance), in the
detection of gases and volatile organic compounds. Efforts focus on
fundamental aspects such as: the use of substrates that enable the
fabrication of LMR and HMR (Hyperbolic Mode Resonance) sensors at
the longest possible wavelengths in the infrared region using materials
like calcium fluoride (CaF2), and the application of artificial intelligence
techniques to enhance the performance of these sensors and enable the
detection of multiple gases., Apoyo financiero del Instituto de Smart Cities de la Universidad Pública de Navarra (Contratos Predoctorales adscritos a Grupos de Investigación de la Universidad Pública de Navarra), el Ministerio de Ciencia e Innovación (PID2019-106231RBI00, PID2022-137437OB-I00 y PDC2023-145831-I00) y beca de movilidad de estudiante del Gobierno 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 Ofiziala (ED 99/2011)

This work exemplifies how incorporating organosilane modifiers into silica matrices allows for tuning the optical response of reflection photonic sensors through customizing the textural properties of hybrid xerogel sensing films. Xerogels with propyl molar percentages 0, 5, and 10% are used to construct photonic probes (OFS0pTEOS, OFS5pTEOS and OFS10pTEOS, respectively) by dip-coating upon optimizing film deposition parameters. The time response of these probes toward a battery of volatile organic compounds (VOCs) comprising species with different functionality, size-shape, and polarity is systematically analyzed through ON/OFF experiments, revealing that a low propyl content makes the poor-responding OFS0pTEOS film highly sensitive toward non-aromatic, large molecules with low-polar or non-polar character in OFS5pTEOS. This sensor is particularly sensitive toward alkanes, with globular cyclohexane (cyHex) outperforming elongated n-hexane. Variable-temperature calibration curves obtained from step-by-step experiments and adsorption-desorption cycles corroborate these observations and allow hysteresis to be quantified. The response to cyHex closely follows VOC concentration changes with the most stable signal among analytes, leading to well-defined curves with low-to-negligible hysteresis. The isosteric enthalpies of cyHex adsorption are obtained for both the bulk material and the sensor, demonstrating labile adsorbate-adsorbent interactions ruling the sensor response and becoming more exothermic for larger VOC concentrations., This work was funded by the Spanish Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (grant numbers PID2020-113558RBC42 and PID2022-137437OB-I00). The authors thank UCTAI (UPNA) for technical support and Dr. A. Ozcáriz for ellipsometry measurements. Open access funding provided by Universidad Pública de Navarra.