Holographic Sensors for the Detection of Liquid Phase Analytes

The aim of this project is to design, fabricate and study experimentally photonic structures created by holographic lithography for application in sensing. The aim is to modify the photonic structures with analyte sensitive materials and view of their application in environmental and biomedical sensing. Two types of photonic structures were investigated in these studies: modified surface relief holographic gratings and volume holographic gratings

Modified Surface Relief Layer Created by Holographic Lithography: Application to Selective Sodium and Potassium Sensing

Point-of-care diagnostics will rely upon the development of low-cost, noncomplex, and easily integrated systems in order to examine biological samples such as blood and urine obtained from the patient. The development of metal ion sensors is a subject of significant relevance for physiological samples. The level of different blood electrolytes, mainly H+, Na+, K+ and Cl− is considerably used to monitor irregular physiologies. The particular challenge in biosensing, and in fact for any other sensor, is signal differentiation between non-specifically bound material and the specific detecting of the target molecule/ion. The biosensors described in this paper are fabricated by a holographic recording of surface relief structures in a photopolymer material. The surface structures are modified by coating with either dibenzo-18-crown-6 (DC) or tetraethyl 4-tert-butylcalix[4]arene (TBC), which are embedded in a polymer matrix. Interrogation of these structures by light allows indirect measurement of the concentration of the analyte. The influence of polymer matrices with different porosities, plasticised polyvinyl chloride (PVC) and a sol-gel matrix, on the performance of the sensors for detection of K+ and Na+ is examined. Here we demonstrate a proof of concept that by using a matrix with higher porosity one can increase the sensitivity of the sensor. The results showed that the DC sensing layer provides a selective response to K+ over Na+ and the TBC modified grating is more responsive to Na+ over K+. The sensor responds to K+ and Na+ within the physiological concentration range

Synthesis of Fast Curing, Water-Resistant and Photopolymerizable Glass for Recording of Holographic Structures by One- and Two-Photon Lithography

Advancements in hybrid sol-gel technology have provided a new class of holographic materials as photopolymerizable glasses. Recently, a number of photosensitive glass compositions with high dynamic range and high spatial resolution have been reported and their excellent capability for volume holography has been demonstrated. Nevertheless, challenges remain, particularly in relation to the processing time and environmental stability of these materials, that strongly affect the performance and durability of the fabricated holograms. State-of-the-art photopolymerizable glasses possess long curing times (few days) required to achieve thick films, thus limiting the industrial implementation of this technology and its commercial viability. This article presents a novel, fast curing, water-resistant, photopolymerizable hybrid sol-gel (PHSG) for holographic applications. Due to introducing an amine-based modifier that increases the condensation ability of the sol-gel network, this PHSG overcomes the problem of long curing time and can readily produce thick (up to a few hundred micrometers) layers without cracking and breaking. In addition, this PHSG exhibits excellent water-resistance, providing stable performance of holographic gratings for up to 400 h of immersion in water. This finding moves photopolymerizable glasses to the next development stage and renders the technology attractive for the mass production of holographic optical elements and their use across a wide number of outdoor applications

Self-processing photopolymer materials for versatile design and fabrication of holographic sensors and interactive holograms

The aim of this paper is to discuss the benefits as well as the limitations of utilizing photopolymer materials in the design of holograms that are responsive to changes in their environment, such as changes in the concentration of a specific substance, temperature, and pressure. Three different case studies are presented, including both surface and volume phase holograms, in order to demonstrate the flexibility in the approach of utilizing holographic photopolymers for the design of sensors and interactive optical devices. First, a functionalized surface relief hologram is demonstrated to operate as an optical sensor for the detection of metal ions in water. The sensitivity and selectivity of the sensor are investigated. The second example demonstrates a volume transmission hologram recorded in a temperature-sensitive photopolymer and the memory effects of its exposure to elevated temperature. Finally, a pressure-sensitive reflection hologram that changes color under application of pressure is characterized, and its potential application in document authentication is described

Ports and Dynamics Colonial: the main ports of the captaincies of northern Brazil

En este artículo se presenta un estudio sobre los principales puertos y lugares de atraque existentes a lo largo de la costa del norte de Brasil, especialmente entre las capitanías de Pernambuco y Ceará, al objeto de probar la dinámica que implican la organización y funcionamiento de los puertos coloniales, dando énfasis en temas acerca de la logística portuaria.This article presents a study on the main ports and places to existing berthing along the coast of northern Brazil, especially among the captaincies of Pernambuco and Ceará, seeking to show the dynamics involving the organization and functioning of the colonial ports, giving emphasis on issues about port logistics

Water Resistant Cellulose Acetate Based Photopolymer for Recording of Volume Phase Holograms

The development of environmentally robust photosensitive materials for holographic recording is crucial for applications such as outdoor LED light redirection, holographic displays and holographic sensors. Despite the progress in holographic recording materials development, their sensitivity to humidity remains a challenge and protection from the environment is required. One approach to solving this challenge is to select substrate such as cellulose acetate, which is water resistant. This work reports the development of a cellulose-based photopolymer with sensitivity of 3.5 cm2/mJ and refractive index modulation of 2.5 × 10−3 achieved in the transmission mode of recording. The suitability for holographic recording was demonstrated by recording gratings with the spatial frequency of 800 linepairs/mm. The intensity dependence of the diffraction efficiency of gratings recorded in 70 μm thick layers was studied and it was observed that the optimum recording intensity was 10 mW/cm2. The robustness of the structures was studied after immersing the layer in water for one hour. It was observed that the diffraction efficiency and the surface characteristics measured before and after exposure to water remain unchanged. Finally, the surface hardness was characterized and was shown to be comparable to that of glass and significantly higher than the one of PVA-based acrylamide photopolymer

Modified Surface Relief Layer Created by Holographic Lithography: Application to Selective Sodium and Potassium Sensing

Point-of-care diagnostics will rely upon the development of low-cost, noncomplex, and easily integrated systems in order to examine biological samples such as blood and urine obtained from the patient. The development of metal ion sensors is a subject of significant relevance for physiological samples. The level of different blood electrolytes, mainly H+, Na+, K+ and Cl− is considerably used to monitor irregular physiologies. The particular challenge in biosensing, and in fact for any other sensor, is signal differentiation between non-specifically bound material and the specific detecting of the target molecule/ion. The biosensors described in this paper are fabricated by a holographic recording of surface relief structures in a photopolymer material. The surface structures are modified by coating with either dibenzo-18-crown-6 (DC) or tetraethyl 4-tert-butylcalix[4]arene (TBC), which are embedded in a polymer matrix. Interrogation of these structures by light allows indirect measurement of the concentration of the analyte. The influence of polymer matrices with different porosities, plasticised polyvinyl chloride (PVC) and a sol-gel matrix, on the performance of the sensors for detection of K+ and Na+ is examined. Here we demonstrate a proof of concept that by using a matrix with higher porosity one can increase the sensitivity of the sensor. The results showed that the DC sensing layer provides a selective response to K+ over Na+ and the TBC modified grating is more responsive to Na+ over K+. The sensor responds to K+ and Na+ within the physiological concentration ranges

LTL type nanozeolites utilized in surface photonics structures for environmental sensors

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In-Situ Ellipsometric Study of the Optical Properties of LTL-Doped Thin Film Sensors for Copper(II) Ion Detection

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