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During the last decades, both governments and companies have been committed to the continuous checking of biological parameters, which can prevent extra costs to administrations. A very efficient way to address this issue is by designing biosensors. This contribution reviews the advances made using optical fibre technology, which have lately agglutinated much of the scientific interest related to the development of biosensors. However, the wide number of publications describing the use of optical fibre for detecting biomarkers has probably blurred the main goal: obtaining portable, simple, easy-to-handle and cost-effective biosensors. With this purpose, this contribution presents some optical fibre structures which have been analysed in terms of several optical parameters of interest from a photonics point of view: sensitivity, quality factor, full width at half minimum, limit of detection and figure of merit. This has made it possible to classify the most advanced optical fibre sensing techniques and, hence, their suitability when developing biosensing applications. ; This work was supported by the Regional Government of Navarra, Spain (projects with references 72/2015 and PC021-022) and by the Agencia Estatal de Investigación (Spanish National Research Agency) through the project with reference TEC2016-78047-R.

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).

Etched optical fiber immunosensors, with and without ITO nanodeposition, have been developed. The performance of these immunosensors has been assessed implementing an immunoassay. The sensitivity of the mmnunosensor increased by a factor of 4 with the ITO nanocoating, whereas the limit of the detection in both types of devices was 0.2 mg/L of antigens in solution. ; This work was supported in part by the Spanish Ministry of Education and Science-FEDER TEC 2016-78047 and by the Government of Navarre through its projects with references: 2017/PI008, 2016/PC025 and 2016/PC026. Besides, was supported in part by the Colombian Administrative Department of Science, Technology and Innovation - Colciencias, through the Program for national doctorates, calling 617 of 2013, and by the project 'Biosensores a fibra optica para la deteccion rapida de enfermedades' supported by the Universidad Nacional de Colombia (Hermes code 40834).

Thin-film coated single-mode–multimode–single-mode (SMS) structures have been analyzed both theoretically and experimentally with the aim of detecting different refractive indices. By adequate selection of the thickness of the thin film and of the diameter of the multimode segment in the SMS structure, a seven-fold improvement can be obtained in the sensitivity of the device to the surrounding medium refractive index, achieving a maximum sensitivity of 1199.18 nm∕refractive index unit for the range of refractive indices from 1.321 to 1.382. Using layer-by-layer self-assembly for deposition, both on the cladding and on the tip of the multimode segment, allows the reflected power to increase, which avoids the application of a mirror on the tip of the multimode segment. ; This work was supported in part by the Spanish Ministry of Education and Science-FEDER TEC2010-17805 and Government of Navarra research grants.

By coating a single-mode–multimode–single-mode (SMS) structure with a high refractive index thin-film it is possible to obtain a transition of modes for specific combinations of thin-film thickness, thinfilm refractive index and surrounding medium refractive index, which permits to develop devices with a high sensitivity to specific parameters. In order to gain a better knowledge of the phenomenon the experimental results are corroborated numerically with the Transfer-Matrix-Method. The influence of losses in the thin-film has also been studied. The results obtained prove that a thin-film coated SMS structure is a simple and costeffective platform for development of sensors and optical filters. ; This work was supported by the Spanish Ministry of Education and Science-FEDER TEC2010-17805 and Government of Navarra research grants.

The performance of E-SMS (Etched Singlemode-Multimode-Singlemode) optical fiber structures as immunosensors has been assessed by the implementation of antibody/antigen immunoassays. Through this procedure it has been proven that E-SMS structures are effective and suitable optical platforms for label-free biosensing. Using the phase shift and tracking the wavelength response it was found that the fabricated E-SMS devices exhibited limits of detection (LOD) down up to concentrations of 0.2mg/L of antigens in solution. This was achieved by coating the E-SMS with an antibody-based biolayer (goat IgG) that is able to determine the presence of anti-goat IgG antigen. Both a wavelength detection and a fast Fourier transform (FFT) analysis technique were used to perform this analysis. The FFT method showed similar results to those observed with the most traditional wavelength analysis, but with the advantage of a simpler detection system that makes unnecessary the use of sophisticated optical interrogators. ; This work was supported in part by the Spanish Ministry of Education and Science - FEDER TEC 2016- 78047 and by the Government of Navarre through its projects with references: 2016/PI044, 2016/PC025 and 2016/PC026. This work was supported in part by the Colombian Administrative Department of Science, Technology and Innovation - Colciencias, through the Program for national doctorates, calling 617 of 2013, and by the project "BIOSENSORES A FIBRA ÓPTICA PARA LA DETECCIÓN RÁPIDA DE ENFERMEDADES" supported by the Universidad Nacional de Colombia (Hermes code 40834).

This contribution shows the monitoring of AC and DC millivoltage signals by means of lossy mode resonances generated by Indium Tin Oxide (ITO) on optical fibers. Sensors were obtained by sputtering ITO thin-films onto 25 mm-length segments of 200 μm bare optical fibers. Depositing a 1 μm thin-film of ITO leads to obtain reduced thin-film resistances of near 340 ohms. This allows the detection of voltage signals by monitoring the wavelength shift of the resonances. Sensitivities up to 40 nm/V can be achieved when tracking sinusoidal signals of a few cents of mV peak-to-peak. This opens the path for further research pursuing the detection of biomedical signals. ; This work has been supported by the Spanish National Research Agency through the project with reference TEC2016-78047-R, by the OPTISENS Government of Navarra Research Project and by a predoctoral research grant of the Public University of Navarra.

The development of an optical fiber refractometer by hydrogen fluoride etching and sputtering deposition of a thin-film of indium tin oxide on a single-mode-multimode-single-mode fiber structure has been analyzed with the aim of improving the sensitivity to the changes of the refractive index (RI) of the external medium. The device is sensitive to the RI changes of the surrounding medium, which can be monitored by tracking the spectral changes of an attenuation band or with a fast Fourier transform (FFT) analysis. By using an optical spectrum analyzer combined with a simple FFT measurement technique, the simultaneous real time monitoring is achieved. The results show that the sensitivity depends on the thin-film thickness. A maximum of 1442 nm/RIU (refractive index unit) in the 1.32–1.35RIUrange has been attained. In addition, a theoretical analysis has been performed, where simu lationsmatched with the experimental results. As a practical appli cation of the developed optical fiber structure, a °Brix (°Bx) sensor has been implemented with a sensitivity of 2.13 nm/°Bx and 0.25 rad/°Bx respectively for wavelength and phase shift detection. ; This work was supported in part by the Agencia Estatal de Investigacion, in part by Fondo Europeo de Desarrollo Regional (TEC2016-78047-R), in part by the Government of Navarre through its projects with references: 2016/PI008, 2016/PC025, and 2016/PC026, and in part by the Colombian Administrative Department of Science, Technology and Innovation—Colciencias, through the Program for national doctorates, calling 617 of 2013.

Trabajo presentado en la Eurosensors 2017 Conference. París, 3–6 de septiembre de 2017. ; An optical fibre refractometer has been developed by etching and deposition of a thin film of indium tin oxide (ITO) on a single-mode-multimode-single-mode (SMS) fibre structure. The interference between modes in this structure is sensitive to the refractive index changes of the surrounding medium, achieving sensitivities of up to 7000 nm/RIU in the 1.333–1.338 RIU range. A salinity sensor has been implemented as a practical application of this proposed structure. Fast Fourier transform (FFT) analysis and tracking of an interference dip were used to monitor the interference between modes obtaining sensitivities of 0.99 nm/PSU and 0.025 rad/PSU, respectively. ; This work was supported in part by the Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-78047-R) and by the Government of Navarre through its projects with references: 2016/PI008, 2016/PC025 and 2016/PC026. As well, it was partially supported by the Colombian Administrative Department of Science, Technology and Innovation - Colciencias, through the Program for national doctorates, calling 617 of 2013.

Trabajo presentado en la Eurosensors 2017 Conference. París, 3–6 de septiembre de 2017. ; In this work, the monitoring of the etching process up to a diameter of 30 µm of two LPFG structures has been compared, one of them had initially 125 µm, whereas the second one had 80 µm. By tracking the wavelength shift of the resonance bands during the etching process it is possible to check the quality of etching process (the 80 µm fibre performs better than de 125 µm fibre), and to stop for a specific cladding mode coupling, which permits to obtain an improved sensitivity compared to the initial structure. ; This work was supported by the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) TEC2016-78047-R and by the Government of Navarre through its projects with references: 2016/PI008, 2016/PC025 and 2016/PC026.

The diameter of long-period fiber gratings (LPFGs) fabricated in optical fibers with a low cutoff wavelength was be reduced by hydrofluoric acid etching, enhancing the sensitivity to refractive index by more than a factor of 3, to 2611 nm/refractive index unit in the range from 1.333 to 1.4278. The grating period selected for the LPFGs allowed access to the dispersion turning point at wavelengths close to the visible range of the optical spectrum, where optical equipment is less expensive. As an example of an application, a pH sensor based on the deposition of a polymeric coating was analyzed in two situations: with an LPFG without diameter reduction and with an LPFG with diameter reduction. Again, a sensitivity increase of a factor of near 3 was obtained, demonstrating the ability of this method to enhance the sensitivity of thin-film-coated LPFG chemical sensors. ; This work was supported by the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-79367-C2-2-R, TEC2016-78047-R), by the Government of Navarre through the project with reference 2017/PI044 and with funding from the Engineering and Physical Sciences Research Council (EPSRC) UK, EP/L010437/1.

This contribution reports the development and characterization of an optical system based on parallel Fiber Bragg Gratings (FBGs) to monitor the movements of the wrist and fingers of a hand. The system consisted of a reflective configuration made of FBGs detecting the movements of the fingers and one more located on the wrist as a reference. All FBGs were multiplexed in order to collect the basic movements of the hand. Fibers were embedded in polydimethylsiloxane for protection and to give flexibility to the optical detection setup. Measurements of strain, angle and torsion were performed during the experiments, obtaining sensitivities up to 1.29 pm/ \mu \varepsilon in strain and 64.23 pm/° in angle. Also, a study on the influence of a single sensor on the performance of the whole system was analyzed for a complete study of this proof of concept. The obtained results present a simple system that can be used to monitor the positions of the hand or for the rehabilitation of patients suffering from neuromotor or post-stroke diseases. ; This work was supported in part by the National Research Agency through the Project from Spanish under Grant TEC2016-78047-R, in part by the Government of Navarra Project from Spanish under Grant SENSMOV: 0011-1365-2017-000135, in part by the Brazilian Projects of Fundação Araucária, in part by the Secretaria de Estado da Ciência, Tecnologia e Ensino Superior do Paraná (SETI), in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), in part by Financiadora de Estudos e Projetos (FINEP), and in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil, under Grant 001.

Trabajo presentado a EUROSENSORS 2014, celebrado en Italia del 7 al 10 de septiembre de 2014. ; In the last 4 years, experimental evidences about the potential use of optical sensors based on Lossy Mode Resonances (LMR) have been presented in the literature. These LMR sensors have some similarities with Surface Plasmon Resonance (SPR) sensors, the gold standard in label-free, real-time biomolecular interaction analysis. In these new LMR sensors, if the non-metallic nanocladding of an optical waveguide fulfills the conditions explained in this work, coupling of light to the cladding modes happens at certain resonance wavelengths, which enables the use of LMR devices as refractometers and opens the door to diverse applications such as in biology and proteomics research. These highly sensitive refractometers have already shown sensitivities higher than 20,000 nm/RIU or 5x10-7 RIU and, given the youth of this field, it is expected to achieve even better values. ; This work was supported by the Spanish Ministry of Economy and Competitiveness-FEDER TEC2010-17805 and Government of Navarra research grants.

According to recent market studies of the North American company Allied Market Research, the field of photonic sensors is an emerging strategic field for the following years and it is expected to garner $18 billion by 2021. The integration of micro and nanofabrication technologies in the field of sensors has allowed the development of new technological concepts such as lab-on-a-chip which have achieved extraordinary advances in terms of detection and applicability, for example in the field of biosensors. This continuous development has allowed that equipment consisting of many complex devices that occupied a whole room a few years ago, at present it is possible to handle them in the palm of the hand; that formerly long duration processes are carried out in a matter of milliseconds and that a technology previously dedicated solely to military or scientific uses is available to the vast majority of consumers. The adequate combination of micro and nanostructured coatings with optical fiber sensors has permitted us to develop novel sensing technologies, such as the first experimental demonstration of lossy mode resonances (LMRs) for sensing applications, with more than one hundred citations and related publications in high rank journals and top conferences. In fact, fiber optic LMR-based devices have been proven as devices with one of the highest sensitivity for refractometric applications. Refractive index sensitivity is an indirect and simple indicator of how sensitive the device is to chemical and biological species, topic where this proposal is focused. Consequently, the utilization of these devices for chemical and biosensing applications is a clear opportunity that could open novel and interesting research lines and applications as well as simplify current analytical methodologies. As a result, on the basis of our previous experience with LMR based sensors to attain very high sensitivities, the objective of this paper is presenting the route for the development of label-free optical waveguide sensing platform based on LMRs that enable to explore the limits of this technology for bio-chemosensing applications. ; This work was supported in part by the Spanish Ministry of Education and Science-FEDER TEC2016- 78047-R, Government of Navarra 0011-1365-2017- 000117 and Public University of Navarra PJUPNA26 research grants as well as the ATTRACT call financed by the European Union's Horizon 2020 research and innovation programme under grant agreement No. 777222.