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This work describes the design of an optomechatronics system controlled with LabVIEW via RS232 serial port. The system, that uses polarized light from a He-Ne laser, is applied in an optical sensing technique by Surface Plasmon Resonance (SPR) in the prism-based Kretschmann configuration, for optical characterization of thin film and biosensing applications. Since the measurements must be of high accuracy and insulated from mechanical noise, optomechatronics system improvements are realized by integrating control of Stepper Motor Rotary Stages that accomplish the required system features. The results showed that the system can yield reliable measurement data and greater precision.

Organic molecular sensors have the advantage of being used through easy, fast, economical and reliable optical methods for detecting toxic metal ions in the environment. In this work, we present a simple but highly specific organic ligand 5-Chloro-2-[(1E,2E)-3-(4-(dimethylamino)phenyl)allylidene)amino)]phenol ( S1 ) that works as a colorimetric sensor of copper ions in aqueous solutions. Binding interaction between S1 and various metal ions was established by UV–Vis spectroscopic measurements showing favorable coordination toward Cu 2+ and practically no interference with the presence of other metal ions, i.e., Cd 2+ , Co 2+ , Cr 2+ , Fe 3+ , Mg 2+ , Ni 2+ , Hg 2+ , Pb 2+ , Mn 2+ , and Zn 2+ . S1 exhibited binding-induced color changes from yellow to pink with a detection limit of 1.25 × 10 −7 M measured by spectroscopic methods, while colorimetric changes could be observed at naked eye for concentrations as low as 2 × 10 −6 M. Furthermore, we also demonstrated that S1 can be useful for sensing copper ions through the use of surface plasmon resonance (SPR) technique. This technique allowed detecting the presence of Cu 2+ in aqueous solutions at the concentration level of ca 1.5 × 10 −6 M due to changes in the refractive index.

Prodigiosin, a natural pigment produced as a secondary metabolite by the non-photosynthetic bacterium Serratia marcescens, was tested as a sensitizer in dye-sensitized solar cells (DSSC). The strain S. marcescens 11E, which was isolated from a natural spring located in the northeastern Mexican state of Nuevo Leon, was cultivated on peanut oil broth 1% v/v, a culture medium which is known to enhance the production of prodigiosin. The resulting pigment was extracted with chloroform and identified as prodigiosin based on the spectroscopic and structural characteristics obtained by UV–Vis spectrophotometry along with FTIR and 1H NMR spectroscopies. The initial absorbance decomposition test performed on the bacterial pigment demonstrated that prodigiosin exhibited high photostability after five days, while the photovoltaic performance test of the sensitized DSSC, resulted in an open voltage circuit of 560 mV, a current density of 0.096 mA/cm2, and efficiency of 0.032%. Structurally, the DSSC consisted of a titanium dioxide (TiO2) photoanode sensitized with the pigment by direct adsorption, an electrolyte containing a redox pair I−/I3− and a cathode or counter electrode prepared from a carbon paste. Since the overproduction of prodigiosin can be easily achieved on a large scale through the rapid fermentation of agro-industrial residues throughout the year without the need to allocate surfaces for the cultivation of pigment-producing plants or wait for specific seasons for their cultivation, our results suggest that prodigiosin could be considered an excellent candidate to be used in the development of a low-tech, low-cost DSSC.

Black Sigatoka is a disease that occurs in banana plantations worldwide. This disease is caused by the hemibiotrophic fungus Pseudocercospora fijiensis, whose infection results in a significant reduction in both product quality and yield. Therefore, detection and identification in the early stages of this pathogen in plants could help minimize losses, as well as prevent the spread of the disease to neighboring cultures. To achieve this, a highly sensitive SPR immunosensor was developed to detect P. fijiensis in real samples of leaf extracts in early stages of the disease. A polyclonal antibody (anti-HF1), produced against HF1 (cell wall protein of P. fijiensis) was covalently immobilized on a gold-coated chip via a mixed self-assembled monolayer (SAM) of alkanethiols using the EDC/NHS method. The analytical parameters of the biosensor were established, obtaining a limit of detection of 11.7 &micro, g mL&minus, 1, a sensitivity of 0.0021 units of reflectance per ng mL&minus, 1 and a linear response range for the antigen from 39.1 to 122 &micro, 1. No matrix effects were observed during the measurements of real leaf banana extracts by the immunosensor. To the best of our knowledge, this is the first research into the development of an SPR biosensor for the detection of P. fijiensis, which demonstrates its potential as an alternative analytical tool for in-field monitoring of black Sigatoka disease.

In this work we propose a virtual instrumentation, user-friendly, computer-controlled instrumentation and data analysis techniques, allowing an instantaneous comparison between theoretical predictions, simulations and actual experimental results. These applications in LabVIEW programming software show a virtual explosion in data acquisition and control system from the laboratory. We consider a versatile opto-mechanical system θ–2θ by using the p-polarized light from a He–Ne laser in which the surface plasmon resonance, Brewster and Brewster-Abeles methods, and scattering measurements are driven by LabVIEW software that produces fast, simple and accurate measurements of samples. The application can be used for both education and specific research purposes.

We report the use of the prism-based surface plasmon resonance (SPR) technique to differentiate between three types of tequilas white or silver, aged, and extra-aged. We used the angular interrogation method in which the structure is based on prism fabricated with BK7 glass coated with a gold layer as the SPR active layer. Our study was centered in the analysis of the resonant angle of the SPR generated by the three types of tequilas produced by the three major tequila-producing firms. We observed that each tequila sample produced a well-differentiated SPR curve. We found that resonant angle of the SPR curve produced by silver tequilas is larger than that produced by the aged and extra-aged tequilas of the same producer firm. We found that the position of the SPR curve is not exclusively determined by the alcohol contents; we believe that there are other parameters derived from the aging process that should be considered. The refractive index of the tequilas used in this study was estimated using the measured resonant angle.

Here we propose two methods using conventional evaporation process to produce tailored Pd/Au composite thin films for hydrogen sensing. In the first method Pd and Au are evaporated simultaneously using different evaporation rate. In the other, alternated nano-layer of Pd and Au are evaporated. Some characteristics of the thin films and their response to hydrogen when they are deposited over optical fibers are experimentally analyzed. Optical fiber sensors for detection of hydrogen concentration lower than 4% and response time of 10 s approximately are demonstrated. The possibility to precisely control the proportion of the constituents of Pd-alloys thin films to produce optical fiber hydrogen sensors with fast response makes these methods very attractive.

Optical microfibers decorated with PdAu nanoparticles are proposed for fast hydrogen sensing. The optical microfibers were fabricated by simply tapering conventional telecommunications fiber down to dimensions comparable to the wavelength of the guided light. The optical microfibers were then coated over a few millimeters with a PdAu layer in island form by depositing the layer at low deposition rate (0.1 A/s). Then the islands were grown with a thermal annealing process until composite nanoparticles were formed. The PdAu nanoparticles deposited on the optical microfibers experience optical and physical changes when they are exposed to hydrogen. This gives rise to reversible transmission changes with an unusual pulsed like behavior which is attributed to scattering of the guided light. The devices are promising for detecting low concentrations of hydrogen (up to 8%) at room temperature with response and recovery times on the order of seconds, i.e., faster than many other hydrogen sensors that exploit phenomena at the nanoscale. The sensing of other gases is also feasible if the optical microfibers are decorated with suitable gas-permeable nanoparticles.

We present an experimental study performed to determine the hydrogen sensing characteristics of a stack of Pd and Au nano-layers. Hetero-core optical fibers were coated with a stack of 1, 2, 3, 4 and 5 double layers of 1.4 nm of Pd and 0.6 nm of Au, alternately deposited by thermal evaporation. The presence of hydrogen produces a decrease in the palladium refractive index, which causes attenuation changes in the optical fiber evanescent wave. Several samples, hetero-core optical fibers coated with different thin film thicknesses, were fabricated and tested in a very simple optical transmission measurement setup. A mixture of hydrogen and nitrogen (carrier gas) was used to test the devices. We observed a response time of 4.5 s for hydrogen concentration of 4%. When hydrogen flow was turned off, the multilayer thin film desorbs the gas in 13 s, indicating a fast recovery response.

Thin alloy film of Pd and Au, formed by simultaneous electron-beam and thermal evaporation techniques, respectively, is used in the design of an optical fiber hydrogen sensor. The sensor consists of a multimode fiber (MMF) in which a short section of single mode fiber (SMF), coated with the Pd–Au thin film, is inserted. Due to core diameter mismatch, the SMF cladding guides light, allowing the interaction between the sensing layer and the guided light. When the sensor is exposed to hydrogen, the Pd–Au layer refractive index diminishes and causes attenuation changes on the transmitted light. Several samples with different layer thickness uniformity were fabricated and tested in a very simple experimental set-up. We have observed that the sensor signal change is dependant on layer thickness uniformity, since the effective interaction length between the evanescent field and the sensing layer is increased. By contrast, such uniformity practically has no influence on the time response of the sensor. The resulting Pd–Au film can detect 4% hydrogen with a response time of 15 s.

We report on optical fiber hydrogen sensors based on absorption changes of evanescent fields caused by a Pd or Pd/Au alloy thin film. The sensor consists of a small piece of standard single-mode fiber (SMF) coated with a palladium or Pd/Au thin film sandwiched between two multimode fibers (MMFs). Due to core diameter mismatch the SMF cladding guides light. When the device is exposed to hydrogen the layer refractive index diminishes and causes attenuation changes of the evanescent fields. Such attenuation changes can be easily detected with a simple transmission measuring setup. Robust sensors with time responses of 15 s and good sensitivity suitable for the detection of hydrogen concentration below the critical 4% are demonstrated.

For an expert nose, the aroma of a beverage is a fingerprint that can be used to certify its authenticity, distinguish between distillation processes, or even identify the raw material used to fabricate it. In this work, we propose a simple, automatic, and repeatable optical method, which can be used as a first and quick test to authenticate tequila samples. This method is based on the measurement of beam intensity changes, using the surface plasmon resonance technique, operating at a fixed angle. We observed that each tequila, depending on the alcohol content and aging process, produces a specific change in measured intensity level.

We report a simple and inexpensive optical fiber hydrogen sensor which consists of a palladium-coated cladded multimode tapered fiber. The working mechanism of such a sensor is based on the absorption changes of the evanescent waves. With a conventional multimode fiber, a low-power LED operating at 850 nm, and a simple detection scheme we demonstrate some sensors. It was found that the sensor's performance can be adjusted with the taper diameter. The sensor is suitable for monitoring concentrations of hydrogen below 4% (the lower explosive limit) with fast response.

Cladded multimode tapered fiber tips with mirrored end are proposed as refractometers. The working mechanism of such devices is based on radiation of the modes guided by the cladding, which is induced by the refractive index of the sample medium. Using conventional graded-index multimode fiber, a low-power 850 nm LED, and a simple detection scheme some inexpensive, robust, and versatile refractometers are demonstrated. The length of the tips is typically 2 mm, while their diameter is less than 80 μm. The refractometers can cover a refractive index range between 1.36 and 1.46 with resolution up to 3 × 10−5.

A new color printing process is based on the photodissociation of spiropyran complexes accelerated by electron transfer with an organic semiconductor. Good quality prints were obtained using an optimum composition with complexes from three different spiropyrans and variable concentration.

The application of the Brewster angle technique and a genetic algorithm for the measurements of refractive index and thickness in tetragonal ZrO 2 :Er 3+ and ZrO 2 –SiO 2 films prepared by the sol–gel process and dip–coating technique annealed at 550°C are reported. A precision higher than 99.5% and 98% in the refractive index and thickness measurements were obtained, respectively. Analysis of the capability to tune the refractive index of high-density blend films by changing the molar concentration of zirconium dioxide, with an increment rate of (0.0052±0.0004)/mol, are also presented.

Bromophenol blue ® (BPB) dyed with the rosin and isopropyl alcohol produces a film with a uniform yellow appearance, which can be deposited on glass plates by simple technique. This mixture shows good photosensitivity in the blue light ( λ =457 nm line) employing argon-ion laser and presents high resolution for holographic application. Consequently, it is possible to obtain holographic elements, e.g., gratings.

We report the use of a single-mode tapered fiber coated with a dispersive material as a tunable band-edge filter. The band-edge wavelength can be adjusted, over a range of /spl sim/500 nm (1150-1650 nm), in a simple way with the taper waist diameter, the interaction length, or with the refractive index of the dispersive material that coats the taper. Moreover, the fabrication procedure is simple and of low cost.

We propose the use of branched gold nanoparticles (B-GNPs) as a contrast agent for optical coherence tomography (OCT) imaging. Our results show that even when the central source of our OCT (1325 nm) is too far from the maximum peak of the plasmon resonance, branched nanoparticles scatter light very efficiently at this wavelength. B-GNPs were tested as a contrast agent in water and agarose-TiO2tissue phantoms; the estimated increments in contrast were 9.19 dB and 15.07 dB for branched nanoparticles in water with concentrations of2.2×109 NPs/mL and6.6×109 NPs/mL, respectively, while for agarose-TiO2tissue phantoms the estimated value was 3.17 dB. These results show the promising application of B-GNPs as a contrast agent for tissue imaging using OCT, not only for sources at 1325 nm but also at other central wavelengths located between 800 and 1000 nm.

Optical microfibers decorated with PdAu nanoparticles are proposed for fast hydrogen sensing. The microfibers were obtained by simply tapering conventional telecommunications fiber down to dimensions comparable to the wavelength of the guided light. A few millimeters of the microfiber were coated with a PdAu layer in island form by depositing the layer at low evaporation rate (0.1 A/s). Then the islands were grown with a thermal annealing process until composite nanoparticles were formed. The PdAu nanoparticles deposited on the optical microfibers experience optical and physical changes when they exposed to hydrogen. This gives rise to reversible transmission changes with an unusual pulsed like behavior which is attributed to scattering of the guided light. The devices are promising for detecting low concentrations of hydrogen (up to 8%) at room temperature with response and recovery times on the order of seconds.

We report an all-optical fiber hydrogen sensor based on absorption changes of evanescent fields caused by an annealed Pd/Au thin film. The sensor consists of a small piece of standard single-mode fiber (SMF) coated with a Pd/Au thin film sandwiched between two multimode fibers (MMFs). Due to core diameter mismatch the SMF cladding guides light. When the device is exposed to hydrogen the layer refractive index diminishes and causes attenuation changes of the evanescent fields. Adding gold to palladium allows the fabrication of fast, durable, and reliable sensors suitable for the detection of hydrogen concentration below the critical 4%.

We present an experimental analysis of the time response of a hydrogen sensor based on a tapered multimode fiber coated with Pd composite thin films. A novel fiber taper coating technique is proposed. The components (Pd and Ag or Pd and Au) are simultaneously deposited over the uniform waist of a tapered fiber at different evaporation rate. Multimode Fiber tapers coated with Pd-Ag and Pd-Au thin films, exposed to 4% hydrogen concentration in pure nitrogen at normal conditions, have shown a time response of 20 and 15 seconds, respectively. The simple detection scheme combined with fast response makes this inexpensive optical fiber hydrogen sensor very attractive.

Metal-coated singlemode tapered optical fibers are demonstrated for high-resolution refractive index sensing. The fundamental fiber mode can excite the different hybrid surface plasmon modes supported by the semi-cylindrical metallic shell. The transmission spectrum of our devices exhibits multiple resonance peaks with either TE- or TM-polarized light. The number of resonance peaks as well their depth depend on the taper diameter and also on the external refractive index. Experimentally we have found that the first two or three resonance peaks are the most sensitive peaks to refractive index changes. We estimate that a resolution of about 2x10 -7 can be achieved with our sensors. Our devices can be used for high-resolution biosensing.

We report on an optical fiber surface plasmon resonance sensor that exhibits multiple resonance peaks. The sensor is based on a uniform-waist single-mode tapered fiber coated on one side with a thin metal layer. Owing to the asymmetry of the sensor structure, the different hybrid surface plasmon modes supported by the semicircular layer can be excited by the fundamental fiber mode. As a result, the sensor transmission spectrum exhibits several dips that depend on the taper waist diameter. The advantages of a plasmon resonance sensor with multiple dips are discussed.

In this work, the surface plasmon resonance (SPR) technique is used to determine the quality or adulteration of tequila beverages. Graphic analyses of the position and width of the SPR curve are related to the complex refractive index of the sample, showing differentiated regions where one can easily and unambiguously identify white, aged, or extra-aged tequilas, and even adulterated or low quality tequilas. The curves generated by aged and extra-aged tequilas, with respect to those obtained from white tequilas, are wider, while the resonant peak shifts towards larger angles. This behavior should be attributed to the aging process. The resonance curve is generated in 20 s, minimizing the variations of the SPR curve parameters due to temperature fluctuations.

The use of uniform-waist cladded multimode tapered optical fibers is demonstrated for evanescent wave spectroscopy and sensors. The tapering is a simple, low-loss process and consists of stretching the fiber while it is being heated with an oscillating flame torch. As examples, a refractive-index sensor and a hydrogen sensor are demonstrated by use of a conventional graded-index multimode optical fiber. Also, absorbance spectra are measured while the tapers are immersed in an absorbing liquid. It is found experimentally that the uniform waist is the part of the taper that contributes most to the sensor sensitivity. The taper waist diameter may also be used to adjust the sensor dynamic range.

A high-speed all-optical switch using a fiber optic coupler and a light-sensitive variable-index material is described. The mechanism of index variation with light is discussed, as well as the results of switching with polydialkylsilane and polythiophene for index modulation.

We present a technique in which the photoresist Shipley® 1350-J absorption spectra is changed when it is mixed with crystal violet® tint previously diluted in isopropyl alcohol. The absorption spectra of this mixture presents an increment of absorption at red light, consequently, it is possible to obtain holographic elements, e.g. gratings, when a HeNe laser is employed to the wavelength of 632.8 nm.

In the present work, the behaviour of rosin resin with crystal violet® tint is shown. This mixture shows good photosensitivity to red light (He–Ne line), and has a high enough resolution for holographic applications. This resin is an excellent basis for this tint, and presents good handling and seems to be a worthy material to make holographic elements

"En este trabajo de tesis se muestra el proceso que se llevó a cabo para la primera etapa de diseño y construcción de un sistema basado en resonancia de plasmones de superficie, así como la actualización de algunas partes de otro sistema de resonancia de plasmones con el que se trabaja actualmente en el laboratorio. Ambos sistemas pueden ser usados en su modalidad de resonancia de plasmones de superficie (en sus dos formas: barrido angular y ángulo fijo) o se pueden adaptar para hacer mediciones mediante la técnica de Abelès-Brewster. En la primera parte de este trabajo se muestran cada una de las componentes que integran ambos sistemas, abarcando la parte óptica, mecánica y electrónica. Se muestran también las interfaces que se desarrollaron en el software Labview, mediante las cuales es posible controlar los sistemas y hacer mediciones. Con estas interfaces también es posible simular el fenómeno de resonancia de plasmones de superficie, realizar el análisis de las curvas experimentales y obtener los parámetros ópticos de películas delgadas (índice de refracción, coeficiente de extinción y grosor). Finalmente, se muestran algunas aplicaciones para este tipo de sistemas, tales como la detección de compuestos aromáticos en tequila, la determinación de los parámetros ópticos de películas delgadas orgánicas e inorgánicas usando los métodos de resonancia de plasmones de superficie y Abelès-Brewster, y un prototipo de biosensor para la detección y diagnóstico de enfermedades agrícolas mediante tecnología combinada de anticuerpos y resonancia de plasmón superficial. Caso Sigatoka negra, como prueba de concepto."

"Esta tesis presenta el diseño y realización de un sistema θ-2θ, el cual puede usarse en su modalidad de resonancia de plasmones de superficie o puede adaptarse a la técnica de Brewster-Abelès. Mediante este sistema, es posible caracterizar películas delgadas metálicas y dieléctricas. Los parámetros que son encontrados, para el caso de las películas delgadas metálicas son los siguientes: curva de resonancia de plasmones, ancho de la curva de resonancia, ángulo de resonancia, altura de la curva, índice de refracción de la película, coeficiente de extinción y espesor. Para las películas delgadas dieléctricas, se encuentra su curva de reflectancia, el ángulo de Brewster y su índice de refracción. El sistema también puede ser usado como un sensor, capaz de medir variaciones en el índice de refracción de muestras líquidas."

"La detección de hidrógeno a bajas concentraciones requiere de sistemas altamente sensibles y muy estables. Los mecanismos de detección se han enfocado en métodos basados en fibras ópticas precisamente por la alta sensibilidad y estabilidad que presentan aún cuando se exponen a atmósferas explosivas y ambientes con campos electromagnéticos intensos. En éste trabajo de tesis proponemos una técnica basada en fibras ópticas estrechadas recubiertas con una película delgada de paladio y oro (Pd/Au). Las fibras ópticas se estrecharon utilizando la técnica de calentamiento y estirado, lo que ocasionó una reducción en el diámetro de la misma. La parte estrechada de la fibra permite la interacción del medio externo con el campo evanescente de la fibra. Para utilizar ésta estructura en la detección del hidrógeno depositamos una película delgada de paladio y oro en la parte adelgazada de la fibra. Cuando la capa delgada de paladio entra en contacto con el hidrógeno, cambia la absorción de la onda evanescente. Estos cambios se midieron con un esquema muy sencillo. Se fabricaron y caracterizaron dos tipos de muestras, las primeras con fibra monomodo convencional (SMF-28) y las otras con fibra microestructurada, los dos tipos de fibra se estrecharon a distintos diámetros, y se recubrieron con películas delgadas de Pd/Au de distinto espesor. Se registraron tiempos de respuesta menores a los 10 segundos a una concentración del 4 % de H2."