Showing papers by "Ignacio R. Matias published in 2011"

Optical fiber pH sensor based on lossy-mode resonances by means of thin polymeric coatings

Abstract: This work describes the fabrication of an optical fiber sensor with spectral response to pH based on the deposition of a thin polymeric coating on an optical fiber core. If the thin polymeric coating has a high refractive index real part and a non-null imaginary part, this permits a coupling of light to the modes guided in the polymeric coating originating optical resonances. These resonances are named by some authors as lossy-mode resonances (LMR) or guided-mode resonances. Moreover, the location of the resonances in the optical spectrum varies as a function of the coating thickness and refractive index. Hence, the utilization of the well-known poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) pH sensitive polymeric coating that presents a variation of the thickness with the pH of the solution (known as swelling/deswelling behaviour) permits the fabrication of optical fiber pH sensors based on wavelength detection. The fabrication of ready-to-use devices requires considering several aspects such as the adequate polymeric coating thickness or the selection of the resonance to be monitored. As a result, LMR-based optical fiber pH sensors with accuracy of ±0.001 pH units and an average sensitivity of 0.027 pH units/nm within the range between pH 3 and pH 6 have been obtained after an adequate design.

An antibacterial coating based on a polymer/sol-gel hybrid matrix loaded with silver nanoparticles

Abstract: In this work a novel antibacterial surface composed of an organic-inorganic hybrid matrix of tetraorthosilicate and a polyelectrolyte is presented. A precursor solution of tetraethoxysilane (TEOS) and poly(acrylic acid sodium salt) (PAA) was prepared and subsequently thin films were fabricated by the dip-coating technique using glass slides as substrates. This hybrid matrix coating is further loaded with silver nanoparticles using an in situ synthesis route. The morphology and composition of the coatings have been studied using UV-VIS spectroscopy and atomic force microscopy (AFM). Energy dispersive X-ray (EDX) was also used to confirm the presence of the resulting silver nanoparticles within the thin films. Finally the coatings have been tested in bacterial cultures of genus Lactobacillus plantarum to observe their antibacterial properties. It has been experimentally demonstrated that these silver loaded organic-inorganic hybrid films have a very good antimicrobial behavior against this type of bacteria.

Optical Fiber Humidity Sensors Using PVdF Electrospun Nanowebs

Abstract: 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.

Simultaneous Measurement of Humidity and Temperature Based on an SiO $_{2}$ -Nanospheres Film Deposited on a Long-Period Grating In-Line With a Fiber Bragg Grating

Abstract: A novel configuration able to measure simultaneously relative humidity and temperature is proposed. The sensing head is based on a long-period fiber grating (LPG) coated with silica nanospheres in-line with a fiber Bragg grating. The polymeric overlay that changes its optical properties when exposed to different humidity levels is deposited onto the LPG using the electrostatic self-assembly technique (ESA), resulting into a humidity-induced shift of the resonance wavelength of the LPG. Considering the humidity range from 20% to 50% RH, a system resolution of 1.6% RH and 2.5°C was achieved. At higher humidity, from 50% to 80% RH, the corresponding resolution values were 2.4% RH and 0.4°C.

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

Abstract: 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.

Humidity sensor based on silver nanoparticles embedded in a polymeric coating

Abstract: In this work, a new humidity sensor based on the deposition of silver nanoparticles embedded in a polymeric coating on an optical fiber core is presented. The silver nanoparticles inside the coating were characterized by transmission electron microscopy (TEM) in order to get additional information about their size and shape. An increase of the Surface Plasmon Resonance (SPR) peak intensity is observed when the coating is built up by using the Layer-by-Layer (LbL) deposition technique. Changes in Relative Humidity from 20% to 80% are detected by a shift of the SPR wavelength.

Lossy mode resonance-based optical fiber humidity sensor

Abstract: In this work it is presented for the first time the fabrication of optical fiber relative humidity (RH) sensors by means of polymeric thin-films as lossy mode resonance (LMR) supporting coatings. In particular, LMRs have been observed thanks to the fabrication of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) polymeric coatings onto cladding-removed multimode optical fibers (CRMMF) employing the Layer-by-Layer (LbL) self assembly method. More than one LMR can be generated as a function of the coating thickness. This generation of multiple LMRs produces a band pass filter with a transmission band in the visible region. PAH/PAA film thickness and refractive index can be modified as a function of the surrounding medium relative humidity (SMRH). Thus, SMRH can be easily determined by measuring the wavelength shift of the transmission band (∼15nm between 20% and 60% RH).

Optimization of single mode fibre sensors to detect organic vapours

Abstract: The construction of single mode optical fibre (SMF) sensors to handle with volatile organic compounds (VOCs), has been optimized to operate at the third telecommunication window (1550 nm). The main motivation is to take advantage of the photonic devices used in telecommunication systems that makes easier sensors multiplexing. Moreover, the low transmission attenuation at that wavelength offers the possibility of remote sensing. The sensing materials used suffer reversible structural alterations in the presence of VOC, such as colour change, which are detectable with a photonic system. Following the Electrostatic Self Assembly method (ESAm), a nanostructure is constructed onto cleaved ended SMF, which is doped with a sensing material. The fabrication of this type of sensors was focused on multimode fibres (MMF) and in the visible spectral range (VIS) so far. The implementation has been adapted to SMF and to operate around 1550 nm, specifically, by easing the adsorption of the VOCs molecules. It has been observed that the sensing material affects the morphology of the nanostructures as well and so, to the sensors response. The devices implemented show a potential use in the identification of single and complex mixtures of VOCs.

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

Abstract: 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.

Analyses of performance of novel sensors with different coatings for detection of Lipopolysaccharide

Abstract: Interdigital sensors have been widely used for non-destructive applications. New types of planar interdigital sensors have been fabricated with different coating materials to assess the response to Lipopolysaccharide, LPS. All the coatings were selected and optimized to be stable in water, as the measurements take place in water media. Moreover, the coatings have been designed to have available carboxylic or amine functional groups. The use of these functional groups is a widely used technique to specifically binding of biomolecules. The coated sensors were then immobilized with Polymyxin B(PmB) which has the specific binding properties to LPS. This paper will highlight the fabrication process and initial investigations on the sensors' performance based on Impedance Spectroscopy.

Optical fiber refractometers based on sputtered indium tin oxide coatings

Abstract: This work presents the fabrication of optical fiber refractometers based on indium tin oxide (ITO) coatings deposited by sputtering with response in the visible spectral region. ITO thin-films have been sputtered by employing a rotating mechanism that enables the fabrication of smooth and homogeneous coatings onto the optical fiber core. Fabricated ITO coated optical fiber devices present several resonances in the visible and near infrared region. These resonances show high optical power attenuations (more than 10 dB) in the visible spectral region, which produces changes in the colour of the output visible light. Therefore, since these resonances shift as a function of the refractive index (RI) of the surrounding medium it is feasible to determine the RI of the outer medium in contact with the ITO coating by simply monitoring the chromatic coordinates (colour change), x and y, of the visible output light.

Optical sensor based on polymer electrospun nanofibers for sensing humidity

Abstract: A novel humidity sensor based on polymer electrospun nanofibers coating onto an optical fiber is proposed in this work. The coating is composed of poly(acrylic acid), and its fabrication was performed by the electrospinning technique using an optical fiber core as substrate. This technique allows the fabrication of sensitive films with high surface area in a fast and simple way compared to other overlay fabrication techniques. The sensor was tested in a programmable temperature and humidity climatic chamber. Relative Humidity (RH) was varied in the range from 20%RH to 80%RH at room temperature. The results showed a monotonic variation of the absorbance spectra to RH changes, thus obtaining a successful humidity sensor.

Resonance-based optical fiber refractometers

Abstract: Here, it is presented a study of optical fiber refractometers based on resonances supported by different thin-film coatings. These coatings consist of different materials, such as noble metals and metal oxides fabricated onto the core of the optical fibers. The dielectric constants of the deposited materials determine the presence of the resonances. Thus, noble metals, such as gold and silver, thanks in part to their negative real part of the optical permittivity enable the generation of surface plasmon resonances (SPR). Meanwhile, conductive metal oxides, such as titanium dioxide (TiO 2 ) and indium tin oxide (ITO), with a positive real part of its optical permittivity make it possible to produce lossy mode resonances (LMR). Gold, silver, TiO 2 and ITO refractometers show sensitivities of 1468, 3617, 114 and 1546 nm/refractive index unit (RIU) respectively. Fabricated devices present a promising platform for the fabrication of multipurpose sensors by the addition of the adequate coating.

Integration of hybrid sensing networks in indoor intelligent homes

Abstract: In this work we present a system based on the integration of different type of sensor technologies at laboratory level A ZigBee temperature sensor prototype has been integrated with a fiber optic sensor network and a KNX sensor network The system also has the capability of remote monitoring in real-time all the different sensor presented in the system