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Publications


Optical Sensitivity Gain in Silica-Coated Plasmonic Nanostructures

F. Floris, C. Figus, L. Fornasari, M. Patrini, P. Pellacani, G. Marchesini, A. Valsesia, F. Artizzu, D. Marongiu, M. Saba, A. Mura, G. Bongiovanni, F. Marabelli, F. Quochi

Ultrathin films of silica realized by sol-gel synthesis and dip-coating techniques were successfully applied to predefined metal/polymer plasmonic nanostructures to spectrally tune their resonance modes and to increase their sensitivity to local refractive index changes. Plasmon resonance spectral shifts up to 100 nm with slope efficiencies of ∼8 nm/nm for increasing layer thickness were attained. In the ultrathin layer regime (<10 nm), which could be reached by suitable dilution of the silica precursors and optimization of the deposition speed, the sensitivity of the main plasmonic resonance to refractive index changes in aqueous solution could be increased by over 50% with respect to the bare plasmonic chip. Numerical simulations supported experimental data and unveiled the mechanism responsible for the optical sensitivity gain, proving an effective tool in the design of high-performance plasmonic sensors. 

 

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

P.J. Rivero, J. Goicoechea, I. R. Matías, F. J. Arregui 

In this work, a comparative study about the incorporation of silver nanoparticles (AgNPs) into thin films is presented using two alternative methods, the in situ synthesis process and the layer-by-layer embedding deposition technique. The influence of several parameters such as color of the films, thickness evolution, thermal post-treatment, or distribution of the AgNPs along the coatings has been studied. Thermal post-treatment was used to induce the formation of hydrogel-like AgNPs-loaded thin films. Cross-sectional transmission electron microscopy micrographs, atomic force microscopy images, and UV-vis spectra reveal significant differences in the size and distribution of the AgNPs into the films as well as the maximal absorbance and wavelength position of the localized surface plasmon resonance absorption bands before and after thermal post-treatment. This work contributes for a better understanding of these two approaches for the incorporation of AgNPs into thin films using wet chemistry.

 

Celiac disease biodetection using lossy-mode resonances generated in tapered single-mode optical fibers

A.B. Socorro, J.M. Corres, I. Del Villar, I.R. Matias, F.J. Arregui

This work presents the development and test of an anti-gliadin antibodies biosensor based on lossy mode resonances (LMRs) to detect celiac disease. Several polyelectrolites were used to perform layer-by-layer assembly processes in order to generate the LMR and to fabricate a gliadin-embedded thin-film. The LMR shifted 20 nm when immersed in a 5 ppm anti-gliadin antibodies-PBS solution, what makes this bioprobe suitable for detecting celiac disease. This is the first time, to our knowledge, that LMRs are used to detect celiac disease and these results suppose promising prospects on the use of such phenomena as biological detectors. 

 

Optical fiber refractometers based on localized surface plasmon resonance (LSPR) and lossy mode resonance (LMR)

P.J. Rivero, M. Hernaez, J. Goicoechea, I. R. Matías, F. J. Arregui 

An optical fiber device showing simultaneously two optical phenomena, localized surface plasmon resonance (LSPR) and lossy mode resonance (LMR), is presented here for the first time. It consists of a fragment of stripped optical fiber coated with a polymeric film that includes gold nanoparticles. The absorption peaks related to both phenomena were captured during the deposition of the coating, showing a different evolution. In addition, the behavior of both phenomena to variations of the surrounding medium refractive index (SMRI) was monitored, studying the different responses of LSPR and LMR. 

 

Optical fiber refractometers based on Lossy Mode Resonances by means of SnO2 sputtered coatings

P. Sanchez, C.R. Zamarreño, M. Hernaez, D. Lopez-Torres, C. Elosua, F.J. Arregui, I.R. Matias

The fabrication of optical fiber refractometers by means of the deposition of a thin tin-dioxide coating onto an optical fiber core is presented. Tin-dioxide permits the guided light in the fiber to be coupled from its core to its coating, creating lossy mode resonances in the infrared and visible regions. These resonances vary as a function of the external medium's refractive index, enabling the fabrication of robust and highly reproducible wavelength-based optical fiber refractometers. Moreover, the first seven lossy modes create seven differentiated resonances which have been studied in the range between 450 and 1650 nm of the optical spectrum. The central wavelength of the resonances can be adjusted by varying the thickness of the tin-dioxide coating.

 

Improved Multifrequency Phase-Modulation Method That Uses Rectangular-Wave Signals to Increase Accuracy in Luminescence Spectroscopy

S. Medina-Rodríguez, A. de la Torre-Vega, F.J. Sainz-Gonzalo, M. Marin-Suárez, C. Elosua, F.J. Arregui, I.R. Matias, J.F. Fernández-Sánchez, A. Fernández-Gutiérrez

We propose a novel multifrequency phase-modulation method for luminescence spectroscopy that uses a rectangular-wave modulated excitation source with a short duty cycle. It is used for obtaining more detailed information about the luminescence system: the information provided by different harmonics allows estimating a model for describing the global frequency response of the luminescent system for a wide range of analyte concentration and frequencies. Additionally, the proposed method improves the accuracy in determination of the analyte concentration. This improvement is based on a simple algorithm that combines multifrequency information provided by the different harmonics of the rectangular-wave signal, which can be easily implemented in existing photoluminescence instruments by replacing the excitation light source (short duty cycle rectangular signal instead of sinusoidal signal) and performing appropriate digital signal processing after the transducer (implemented in software). These claims have been demonstrated by using a well-known oxygen-sensing film coated at the end of an optical fiber [a Pt(II) porphyrin immobilized in polystyrene]. These experimental results show that use of the proposed multifrequency phase-modulation method (1) provides adequate modeling of the global response of the luminescent system (R2 > 0.9996) and (2) decreases the root-mean-square error in analytical determination (from 0.1627 to 0.0128 kPa at 0.5 kPa O2 and from 0.9393 to 0.1532 kPa at 20 kPa O2) in comparison with a conventional phase-modulation method based on a sinusoidally modulated excitation source (under equal luminous power conditions).

 

Spectral width reduction in lossy mode resonance-based sensors by means of tapered optical fibre structures

A.B. Socorro, I.D. Villar, J.M. Corres, F.J. Arregui, I.R. Matias

This contribution pursues the goal of achieving an optical fibre-based platform to detect anti-gliadin antibodies (AGAs), in order to early diagnose celiac disease. To this purpose, the generation of lossy mode resonances (LMRs) in several evanescent field optical structures was studied both theoretically and experimentally. LMRs were obtained by adsorbing a polymeric thin-film onto the optical structures using the layer-by-layer assembly technique. The LMR shape depends on the geometry of the optical structure and its attenuation was controlled just by tuning the length of the device. The best performance was obtained with tapered single-mode optical fibres, which provided more than a 50% reduction in the spectral width of the LMR by using a shorter device. This improvement was successfully applied to detect anti-gliadin antibodies (AGAs) in 5 ppm concentration, what can be used to diagnose celiac disease, and shows the potential of this technology to address biosensing applications.

 

A Fiber Optic Ammonia Sensor Using a Universal pH Indicator

A.J. Rodríguez, C.R. Zamarreño, I.R. Matias, R.F. Domínguez, D.A. May-Arrioja

A universal pH indicator is used to fabricate a fiber optic ammonia sensor. The advantage of this pH indicator is that it exhibits sensitivity to ammonia over a broad wavelength range. This provides a differential response, with a valley around 500 nm and a peak around 650 nm, which allows us to perform ratiometric measurements. The ratiometric measurements provide not only an enhanced signal, but can also eliminate any external disturbance due to humidity or temperature fluctuations. In addition, the indicator is embedded in a hydrophobic and gas permeable polyurethane film named Tecoflex®. The film provides additional advantages to the sensor, such as operation in dry environments, efficient transport of the element to be measured to the sensitive area of the sensor, and prevent leakage or detachment of the indicator. The combination of the universal pH indicator and Tecoflex® film provides a reliable and robust fiber optic ammonia sensor.

 

Sensitivity enhancement of a humidity sensor based on poly (sodium phosphate) and poly (allylamine gydrochloride)

M. Hernaez, D. Lopez-Torres, C. Elosua, F.J. Arregui, I.R. Matias

The particular behavior of poly(sodium phosphate) (PSP) when it is deposited by means of the spraying layer-by-layer (LbL) technique has been used here to enhance the response of optical fiber humidity sensors. The roughness of the PSP films varies depending on the concentration of the polymeric solutions. In this work, it is demonstrated that this special feature of PSP allows the fabrication of optical fiber humidity sensors with different responses. Particularly, multilayer thin-films made of 10-3 and 10-4 M PSP and poly(allylamine hydrochloride) (PAH) solutions have been studied and used for the fabrication of optical fiber interferometers sensitive to humidity. To our knowledge this is the first time that the spray-assisted LbL technique has been used for the fabrication of optical fiber sensors.

 

Sensitivity enhancement in a multimode interference-based SMS fibre structure coated with a thin-film: Theoretical and experimental study 

A.B. Socorro, I.D. Villar, J.M. Corres, F.J. Arregui, I.R. Matias

Multimode interference in a single-mode-multimode-single-mode (SMS) fibre structure leads to the generation of transmission bands and attenuation bands in the optical spectrum. in this work, the progressive deposition, with layer-by-layer assembly technique, of a high refreactive index thin-film onto the SMS structure permits to observe the evolution of the bands as a function of the coating thickness. The results show that it is possible to increase the sensitivity of the device to variations of the coating thickness, what indicates the adequateness of this structure as a sensing platform. The experimental results are corroborated with a numerical method based on coupled-mode theory. As a practical application, a sensitivity improvement has been obtained a pH sensor by increasing the coating thickness.

 

Comparative study of layer-by-layer deposition techniques for poly(sodium phosphate) and poly(allylamine hydrochloride) 

C. Elosua, D. Lopez-Torres, M. Hernaez, I.R. Matias, F.J. Arregui

An inorganic short chain polymer, poly(sodium phosphate), PSP, together with poly(allylamine hydrochloride), PAH, is used to fabricate layer-by-layer (LbL) films. The thickness, roughness, contact angle, and optical transmittance of these films are studied depending on three parameters: the precursor solution concentrations (10-3 and 10-4 M), the number of bilayers deposited (20, 40, 60, 80, and 100 bilayers), and the specific technique used for the LbL fabrication (dipping or spraying). In most cases of this experimental study, the roughness of the nanofilms increases with the number of bilayers. This contradicts the basic observations made in standard LbL assemblies where the roughness decreases for thicker coatings. In fact, a wide range of thickness and roughness was achieved by means of adjusting the three parameters mentioned above. For instance, a roughness of 1.23 or 205 nm root mean square was measured for 100 bilayer coatings. Contact angles close to 0 were observed. Moreover, high optical transmittance is also reported, above 90%, for 80 bilayer films fabricated with the 10-4 M solutions. Therefore, these multilayer structures can be used to obtain transparent superhydrophilic surfaces.

 

Tunable electro-optic wavelength filter based on lossy-guided mode resonances 

J.M. Corres, J. Ascorbe, F.J. Arregui, I.R. Matias 

In this work an optical fiber tunable filter based on lossy guided-mode resonances (LGMR) is proposed. It consists of a multilayer structure deposited onto the surface of a plastic cladding removed multimode fiber. The first layer is used to generate the LGMR and to work as the first electrode as well; the second one to tune the filter and the outer layer forms the other electrode. The fabricated filter has demonstrated a good sensitivity to the applied voltage showing a change of the LGMR wavelength of 0.4 nm/V. Among other applications, this filter is intended to be used as electro-optic wavelength filter or modulator.

  

High sensitivity optical fiber pH sensor using poly (acrylic acid) nanofibers 

J.M. Corres, F.J. Arregui, I.R. Matias, Y. Rodriguez 

In this work a new optical fiber pH sensor based on the deposition of poly(acrylic acid) (PAA) using the electrospinning technique is presented. The optical fiber structure consists of a 4 cm segment of hollow core fiber (50/150μm) spliced between two standard multimode fibers onto which the nanoweb is deposited. The sensitive layer is a membrane composed by PAA nanofibers deposited onto the surface of an optical fiber. The sensor has a repetitive behavior and low hysteresis in the pH range 4–7, with an average sensitivity of 0,53 dB/pH.

 

Multicolor Layer-by-Layer films using weak polyelectrolyte assisted synthesis of silver nanoparticles 

P.J. Rivero, J. GoicoecheaA. Urrutia, I. R. Matías, F. J. Arregui 

In the present study, we show that silver nanoparticles (AgNPs) with different shape, aggregation state and color (violet, green, orange) have been successfully incorporated into polyelectrolyte multilayer thin films using the layer-by-layer (LbL) assembly. In order to obtain colored thin films based on AgNPs is necessary to maintain the aggregation state of the nanoparticles, a non-trivial aspect in which this work is focused on. The use of Poly(acrylic acid, sodium salt) (PAA) as a protective agent of the AgNPs is the key element to preserve the aggregation state and makes possible the presence of similar aggregates (shape and size) within the LbLcolored films. This approach based on electrostatic interactions of the polymeric chains and the immobilization of AgNPs with different shape and size into the thin films opens up a new interesting perspective to fabricate multicolornanocomposites based on AgNPs.

 

A Lossy Mode Resonance optical sensor using silver nanoparticles-loaded films for monitoring human breathing.

Pedro J. Rivero, A. Urrutia, J. Goicoechea, I. R. Matías, F. J. Arregui

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

 

Fiber-optic biosensor based on lossy mode resonances

Socorro, A.B., Villar, I.D. ,  Corres, J.M. ,  Arregui, F.J. ,  Matias, I.R.

In this work, a novel fiber-optic immunoglobulin G biosensor based on lossy mode resonances is proposed. This physical phenomenon is obtained by depositing a PAH/PSS layer-by-layer thin-film on a cladding removed optical fiber. A reflective configuration is used to track the generation and response of the electromagnetic resonance in the different phases of the process. According to the results, wavelength displacements of 10 nm are visualized when detecting immunoglobulins with a response time of 12 min for a 50 μg/ml concentration. 

 

Optical fiber humidity sensors based on Localized Surface Plasmon Resonance (LSPR) and Lossy-mode resonance (LMR) in overlays loaded with silver nanoparticles.

Pedro J. Rivero, A. Urrutia, J. GoicoecheaF. J. Arregui

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

 

Tapered Single-Mode Optical Fiber pH Sensor Based on Lossy Mode Resonances Generated by a Polymeric Thin-Film

Socorro, A.B., Villar, I.D. ,  Corres, J.M. ,  Arregui, F.J. ,  Matias, I.R.

Lossy mode resonances can be generated with certain polymeric nanostructures, such as those obtained with a multilayered assembly of poly(allylamine hydrochloride) and poly(acrylic acid). This coating is adsorbed by the electro-static self-assembly technique onto a tapered single-mode optical fiber, in order to evaluate its performance when detecting pH. According to the results reported in this paper, the high sensitivity given by a tapering process in a single-mode optical fiber is increased by the effect of this kind of electromagnetic resonances. Particularly, in a pH range from 4.0 to 6.0, the overall wavelength shift of this sensor reaches 200 nm, and the transmission at the resonance wavelengths can fall down to -50 dB. These data provide results which can be taken into account to detect pH with high accuracy. 

 

A novel luminescent optical fibre probe based on immobilized tridentate bis(phosphinic amide)...

F.J. Sainz-Gonzalo, C. Elosua, J.F. Fernández-Sánchez, C. Popovici, I. Fernández, F.L. Ortiz, F.J. Arregui, I.R. Matias, A. Fernández-Gutiérrez

A novel optical fibre probe based on a tridentate bis(phosphinic amide)-phosphine oxide PhPO(C6H4POPhN(CH(CH3)2)2)2 (ligand 1) has been developed for the detection of europium(III) ions in water. The dip coating technique was used to deposit the ligand 1 encapsulated on a poly(vinyl chloride) membrane onto an optical fibre. The optimum deposition thickness of the membrane was 280 ± 40 nm. The sensing mechanism relies on the reaction between europium(III) ion and ligand 1, which produces a strong luminescent complex of stoichiometry 1:2 Eu(III):Ligand 1 with a maximum emission peak around 612 nm. Two different configurations, aerial and aqueous, were tested for measuring the luminescence off-line and on-line, respectively. The proposed probe showed a response time of 92 s in the aqueous configuration (in situ detection of europium(III) ions in water). The luminescence of the proposed probe displayed a power-law response for the europium(III) concentration in a broad range of concentrations of at least 5 orders of magnitude, from 10 nM to 1 mM, with a correlation coefficient (R2) of the fitted curve better than 0.99.

 

Lossy mode resonances dependence on the geometry of a tapered monomode optical fiber

Socorro, A.B., Villar, I.D. ,  Corres, J.M. ,  Matias, I.R.,  Arregui, F.J. ,

The geometry of a tapered single-mode optical fiber influences the formation and sensitivity of lossy mode resonances generated by the deposition of a polymeric thin-film employing the layer-by-layer electrostatic self assembly technique. In this work, several waist diameters and waist lengths of a monomode optical fiber are analyzed both experimentally and theoretically to obtain some conclusions about their influence on the behavior of this kind of devices. The transmitted optical power is studied as a function of the wavelength to estimate the sensitivity of this system. According to the results obtained, this sensitivity increases as a function of the waist length, whereas it decreases as a function of the waist diameter. What is more, depending on the combination of waist length and waist diameter, important power changes up to 45 dB can be reached at specific wavelength ranges of the electromagnetic spectrum, which can be used for accurate detection of small changes in the nanocoating properties induced by a specific analyte. This behavior can lead to sensing applications based on the combination of lossy mode resonances and tapered monomode optical fibers.

 

Humidity sensor based on silver nanoparticles embedded in a polymeric coating

Pedro J. Rivero, Aitor Urrutia, Javier Goicoechea, Francisco J. Arregui, Ignacio R. Matías

In this work, it is presented a novel optical fiber humidity sensor based on silver nanoparticle-loaded polymeric coatings built onto an optical fiber core. The polymeric film was fabricated using the Layer-by-Layer assembly technique. The silver nanoparticles (Ag NPs) were characterized using transmission electron microscopy (TEM and UV-VIS spectroscopy. A Localized Surface Plasmon Resonance (LSPR) attenuation band is observed when the thickness of the coating increases, and showed a very good sensitivity to Relative Humidity (RH) variations, suitable for high performance applications such as human breathing monitoring.

 

Influence of Waist Length in Lossy Mode Resonances Generated With Coated Tapered Single-Mode Optical Fibers.

Socorro, A.B.;  Del Villar, I.; Corres, J.M.; Arregui, F.J.; Matias, I.R.;

In this work, the generation of electromagnetic resonances due to the deposition of a nanocoating on a tapered single-mode optical fiber is analyzed. The layer-by-layer technique is used to control the thickness of the nanocoating. According to the results that have been obtained, the depth of the resonance depends on the length of the waist region. Variations in the transmitted optical power of 40 dB are observed in just a few layers. This can be considered in the fabrication of both highly sensitive resonance-based sensors and optical filters.

 

Optical Fiber Humidity Sensors using PVdF Electrospun Nanowebs

Corres, J.M.; Rodriguez, Y.R.; Arregui, F.J.; Matias, I.R.;

In this paper, a new optical fiber humidity sensor based on PVdF nanowebs is presented. The electrospinning technique has been used to create a nanometric scale membrane onto the surface of a hollow core fiber (HCF). The fabricated sensor has demonstrated a repetitive response in the range from 50 to 70 % of relative humidity with a rise time of 100 ms. Among other applications, this sensor is intended to be used for monitoring the human breathing. Therefore, high dynamic performances are required, especially in the higher relative humidity ranges.

 

Lossy Mode Resonance-based pH sensor using a tapered single mode optical fiber coated with a polymeric nanostructure

Socorro, A.B.;  Del Villar, I.; Corres, J.M.; Arregui, F.J.; Matias, I.R.;

This contribution presents a pH sensor based on the combination of two technologies: tapered standard-single mode optical fiber (S-SMF) and an electromagnetic resonance phenomenon called Lossy Mode Resonance (LMR). This last phenomenon is produced by coating the optical structure with a thin polymeric film, which for specific values of the coating refractive index and thickness causes a maximum coupling of light guided in the tapered S-SMF region. Layer-by-layer electrostatic self assembly technique was used for the fabrication of a polymeric sensing nanostructure. The construction process was optimized in order to visualize the LMR behavior with a device length of 5 mm. The sensing combination produces a 250 nm wavelength-shift and a 20 dB attenuation variation of the LMR when varying the pH from 4 to 6.