Modelado y simulación de un sensor de fibra óptica basado en la onda evanescente

The development and progress in fiber optic sensors (SFO) is due to the unique advantages they have over solid-state sensors, their main advantages are: immunity to electromagnetic interference, high sensitivity and possibility of distributed sensing, so they have found applications in a variety of fields because most of the physical and chemical variables can be monitored with SFO. One of the main detection mechanisms is the absorption of evanescent waves, so it is important to know the parameters that determine the behavior of this in SFOs. In this work we present the mathematical modeling and simulation to determine the parameters such as evanescent wave absorption and penetration depth. According to the numerical results, an evanescent wave absorption of 0.2x10-3 ua and a penetration depth of 2 µm were obtainedEl desarrollo y avance en los sensores de fibra óptica (SFO) se debe a las ventajas únicas que poseen sobre los sensores basados estado sólido, sus principales ventajas son: inmunidad a las interferencias electromagnéticas, alta sensibilidad y posibilidad de sensado distribuido, por lo cual han encontrado aplicaciones en una gran variedad de campos debido a que la mayoría de las variables físicas y químicas pueden ser monitoreadas con los SFO. Uno de los principales mecanismos de detección es la absorción de ondas evanescentes, por lo que es importante conocer los parámetros que determinan el comportamiento de esta en los SFO. En este trabajo se describe el modelado matemático y simulación para determinar los parámetros como la absorción de la onda evanescente y la profundidad de penetración. De acuerdo con los resultados numéricos se obtuvo una absorción de la onda evanescente de 0.2x10-3 ua, y profundidad de penetración de 2 µm

SERS Detection of Methylene Blue and Crystal Violet Using Silver Nanostars

In this work, silver nanostars were synthesized using silver nitrate, ascorbic acid and polyvinylpyrrolidone (PVP), where the concentration of PVP varied from 0.1 to 10 mM. The morphology was studied by scanning electron microscopy where it was observed that the diameter decreases as the PVP concentration decreases. By UV–Vis absorption measurements typical nanostar spectra were found. In addition, surface-enhanced Raman spectroscopy (SERS) substrates were fabricated by depositing silver nanostars over copper film to detect methylene blue and crystal violet. This study allowed us to identify nanostars as an excellent nanostructure for the fabrication of ultrasensitive SERS substrates for the detection of persistent organic pollutants

Estudio comparativo de la bioactividad de dos materiales biocerámicos

Calcium silicate-based materials have been shown to be bioactive due to their ability to produce biologically compatible carbonated apatite. The objective of this study was to analyze the bioactivity of Biodentine ™ and MTA Repair HP® in contact with human dentine discs, which were sealed and divided randomly to form four groups: group 1 Biodentine™, group 2 MTA Repair HP®, positive control group MTA Angelus® and negative control group IRM®, which were incubated in PBS solution for 10 days, for a subsequent analysis by means of MEB-EDS and Raman spectroscopy. The three calcium-based materials analyzed in this study proved to be bioactive because upon contact with a phosphate-based solution they were triggered at the onset of amorphous calcium phosphate, as the precursor during the formation of carbonated apatite.Los materiales a base de silicato de calcio han demostrado ser bioactivos debido a su capacidad para producir apatita carbonatada biológicamente compatible. El objetivo de este estudio fue analizar la bioactividad de Biodentine™ y MTA Repair HP® en contacto con discos de dentina humana, que se obturaron y dividieron aleatoriamente para formar cuatro grupos: grupo 1 Biodentine™, grupo 2 MTA Repair HP®, grupo control positivo MTA Angelus® y grupo control negativo IRM®, los cuales se incubaron en solución PBS durante 10 días, para posterior análisis por medio de MEB-EDS y Espectroscopía Raman. Los tres materiales a base de silicato de calcio analizados en este estudio demostraron ser bioactivos pues al entrar en contacto con una solución a base de fosfato desencadenaron la precipitación inicial de fosfato de calcio amorfo, que actúa como precursor durante la formación de apatita carbonatada

Photoreflectance and Raman Study of Surface Electric States on AlGaAs/GaAs Heterostructures

Photoreflectance (PR) and Raman are two very useful spectroscopy techniques that usually are used to know the surface electronic states in GaAs-based semiconductor devices. However, although they are exceptional tools there are few reports where both techniques were used in these kinds of devices. In this work, the surface electronic states on AlGaAs/GaAs heterostructures were studied in order to identify the effect of factors like laser penetration depth, cap layer thickness, and surface passivation over PR and Raman spectra. PR measurements were performed alternately with two lasers (532 nm and 375 nm wavelength) as the modulation sources in order to identify internal and surface features. The surface electric field calculated by PR analysis decreased whereas the GaAs cap layer thickness increased, in good agreement with a similar behavior observed in Raman measurements (IL-/ILO ratio). When the heterostructures were treated by Si-flux, these techniques showed contrary behaviors. PR analysis revealed a diminution in the surface electric field due to a passivation process whereas the IL-/ILO ratio did not present the same behavior because it was dominated by the depletion layers width (cap layer thickness) and the laser penetration depth

Influence of Ag Photodeposition Conditions over SERS Intensity of Ag/ZnO Microspheres for Nanomolar Detection of Methylene Blue

Surface enhanced Raman spectroscopy (SERS) is considered a versatile and multifunctional technique with the ability to detect molecules of different species at very low molar concentration. In this work, hierarchical ZnO microspheres (ZnO MSs) and Ag/ZnO MSs were fabricated and decorated by hydrothermal and photodeposition methods, respectively. For Ag deposition, precursor molar concentration (1.9 and 9.8 mM) and UV irradiation time (5, 15, and 30 min) were evaluated by SEM, TEM, X-ray diffraction and Raman spectroscopy. X-ray diffraction showed a peak at 37.9° corresponding to the (111) plane of Ag, whose intensity increases as precursor concentration and UV irradiation time increases. SEM images confirmed the formation of ZnO MSs (from 2.5 to 4.5 µm) building by radially aligned two-dimensional ZnO nanosheets with thicknesses below 30 nm. The Raman spectra of Ag/ZnO MSs exhibited a vibration mode at 486 cm−1 which can be directly associated to Ag deposition on ZnO MSs surface. The performance of SERS substrate was evaluated using rhodamine 6G. The SERS substrate grown at 9.8 mM during 30 min showed the best SERS activity and the ability to detect methylene blue at 10−9 M