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We have developed a multi-array side-polished optical-fiber gas sensor for the detection of volatile organic compound (VOC) gases. The side-polished optical-fiber coupled with a polymer planar waveguide (PWG) provides high sensitivity to alterations in refractive index. The PWG was fabricated by coating a solvatochromic dye with poly(vinylpyrrolido...
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... is the phenomenon whereby a chemical substance changes color due to changes in the solvent polarity of the surrounding environment. A bathochromic (red) shift of the ultraviolet/visible absorption band with increasing solvent polarity is called “ positive solvatochromism. ” The corresponding hypsochromic (blue) shift [21,22] with increasing solvent polarity is called “ negative solvatochromism. ” A schematic diagram of solvatochromism is shown in Figure 2. Dyes that exhibit solvatochromism are called solvatochromic dyes or solvatochromic compounds. A solvatochromic effect or solvatochromic shift refers to a strong dependence of the absorption and emission spectra of a compound on the solvent polarity [22]. Because the polarities of the ground and excited states of a chromophore are different, a change in the solvent polarity leads to differential stabilization of the ground and excited states, and therefore a change in the energy gap between these electronic states. Consequently, variations in the position, intensity, and shape of the absorption spectrum can be direct measures of the specific interactions between the solute and solvent molecules. A solvatochromic dye was used on the sensing membrane [22]. The refractive index of the sensing membrane changed depending on the CT characteristics. A sensor array consisting of five different solvatochromic dyes, such as Nile red [21], Reichardt ’ s dye (R-dye) [22], ...
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... Then, the results suggested that a less polar excited state than the initial state (ground state) will be better established in less polar or non-polar solvents, requiring higher energy for excitement, and leading to a hypsochromic shift of the maximum absorption (negative solvatochromism). [29][30][31][32] This explains the behavior of ITA in the polar solvents EtOH (λ max = 221 nm), MeCN (λ max = 222 nm), and EtOAc (λ max = 254 nm). Moreover, EtOH is a polar protic solvent, with the ability to act as a hydrogen bond donor, which can induce the formation of stable solute-solvent interactions in the ground or excited electronic states, resulting in changes in the absorption shift. ...
Vegetable oils are alternatives to producing renewable monomers since they are biomass. It is possible to react them with anhydrides by heating to provide monomers with high reactivity. However, after the reaction of grape seed oil with itaconic anhydride, it was observed the occurrence of parallel reactions that had not been observed when the same oil was reacted with maleic anhydride. Some articles in the literature have reported that temperature and bases can isomerize itaconic anhydride into citraconic anhydride, which is more stable at room temperature. However, they have not focused on completely understanding how this phenomenon occurred nor studied it in processes that involve microwave irradiation. Therefore, this paper presents a complete characterization and investigation of the thermal behaviour of itaconic anhydride and how it can affect the monomer synthesis performed under heating
... Referring to the sensor-signal testing techniques, existing systems usually focus on the singular measurement of individual physical parameters, such as electrical properties [8,[12][13][14], optical properties [15][16][17][18][19], thermal properties [20], surface acoustic waves (SAW) [21], and photoacoustic spectra (PAS) [22]. On the other hand, fewer systems are capable of the simultaneous measurement of multiple signals [23]. ...
Gas sensing performance characterization systems are essential for the research and development of gas sensing materials and devices. Although existing systems are almost completely automatically operated, the accuracies of gas concentration control and of pressure control and the ability to simultaneously detect different sensor signals still require improvement. In this study, a high-precision gas sensing material characterization system is developed based on vacuum technology, with the objective of enabling the precise and simultaneous measurement of electrical responses. Because of the implementation of vacuum technology, the gas concentration control accuracy is improved more than 1600 times, whereas the pressure of the test ambient condition can be precisely adjusted between vacuum and 1.2 bar. The vacuum-assisted gas-exchanging mechanism also enables the sensor response time to be determined more accurately. The system is capable of performing sensitivity, selectivity, and stability tests and can control the ambient relative humidity in a precise manner. More importantly, the levels of performance of three different optical signal measurement set-ups were investigated and compared in terms of detection range, linearity, noise, and response time, based on which of their scopes of application were proposed. Finally, single-period and cyclical tests were performed to examine the ability of the system to detect optical and electrical responses simultaneously, both at a single wavelength and in a spectral region.
... The counterpart of this approach is that the colour change information in the VIS is not used and, although there are materials specifically designed to show their solvatochromism in the NIR region, multiplexing techniques will only use a spectral span of a few nanometres for each sensor [68]. In these cases, transduction mechanisms based on evanescent wave can also be applied: depending on the type of fibre and material, transmitted power attenuation or the shift of optical resonances [69] (see Figure 11.11). ...
This chapter lists the advantages of using optical fibre as technology for gas or volatile organic compounds (VOC) sensing, emphasizing the possibility of multiplexing. It describes sensing materials used to develop optical fibre sensors (OFSs) with the aim of detecting gases and VOCs. The chapter explains the different mechanisms of transduction of OFSs. It is exclusively dedicated to optical fibre humidity sensors and their most recent researches. The chapter encompasses the devices used for the identification and sensing of VOCs. It explains the artificial systems used for the detection of complex mixtures of VOCs (optoelectronic noses). In order to confirm if an OFS can be used to detect VOCs, several parameters related to static and dynamic responses of the sensors have to be studied. The main and most important parameters are: sensitivity, detection limit, selectivity, resolution, response time, recovery time, and stability.
... VOCs are one of the four organic compounds classified as very quickly volatile or semi-volatile organic compounds included with particulate (especially organic) volatile organic materials [135]. ...
Titanium dioxide (TiO2) has been extensively investigated in interdisciplinary research (such as catalysis, energy, environment, health, etc.) owing to its attractive physico-chemical properties, abundant nature, chemical/environmental stability, low-cost manufacturing, low toxicity, etc. Over time, TiO2-incorporated building/construction materials have been utilized for mitigating potential problems related to the environment and human health issues. However, there are challenges with regards to photocatalytic efficiency improvements, lab to industrial scaling up, and commercial product production. Several innovative approaches/strategies have been evolved towards TiO2 modification with the focus of improving its photocatalytic efficiency. Taking these aspects into consideration, research has focused on the utilization of many of these advanced TiO2 materials towards the development of construction materials such as concrete, mortar, pavements, paints, etc. This topical review focuses explicitly on capturing and highlighting research advancements in the last five years (mainly) (2014-2019) on the utilization of various modified TiO2 materials for the development of practical photocatalytic building materials (PBM). We briefly summarize the prospective applications of TiO2-based building materials (cement, mortar, concretes, paints, coating, etc.) with relevance to the removal of outdoor/indoor NOx and volatile organic compounds, self-cleaning of the surfaces, etc. As a concluding remark, we outline the challenges and make recommendations for the future outlook of further investigations and developments in this prosperous area.
... Además, QUE mostró un desplazamiento batocrómico (16 nm), que correspondería a un aumento en la polaridad alrededor del ANS, explicado por el desplazamiento de esta molécula de la región apolar de la enzima hacia el exterior de la proteína más polar (Lee et al., 2014). La disminución en la fluorescencia generada por los flavonoides como QUE, se puede deber a cambios de polaridad del medio que rodea al ANS, por un desplazamiento de este por parte del flavonoide o por cambios estructurales de la proteína por la interacción flavonoide-lipasa (Martinez-Gonzalez et al., 2017). ...
Pancreatic lipase is a key enzyme in lipid metabolism. Flavonoids are bioactive compounds obtained from vegetables with big relevance, due to their intrinsic interaction with digestive enzymes. Pancreatic lipase activity was evaluated in the presence of flavonoids, through UV-Vis spectroscopy. All tested flavonoids showed a mixed-type inhibition, except catechin, which showed a uncompetitive inhibition. The best inhibitor was quercetin followed by rutin > luteolin > catechin > hesperetin, with IC50 values of 10.30, 13.50, 14.70, 28.50 and 30.50 µM, respectively. The flavonoids inhibitory capacity was related to structural properties shared between the different flavonoids, such as the hydroxylation at C5, C7 (ring A), C2’ and C3’ (ring B), and the double bond between C2 and C3 (ring C). The inhibition results are in agreement with the extrinsic fluorescence analysis. Molecular docking studies indicated that the interaction between pancreatic lipase and flavonoids was mainly through hydrophobic interactions (pi-stacking). The interactions of all flavonoids, except rutin, occurred at the same enzyme site (subsite 1). Instauration between C2 and C3 was decisive for the arrangement of flavonoids with the enzyme, mainly due to pi-stacking interactions.
... The performances of various colorimetric and optical sensors towards gaseous VOCs are presented in Tables 2 and 3. The lowest DL value of 9 ppb was noted for a multi-array side-polished optical fiber fitted with a polymer planar waveguide (PWG) towards five VOCs (benzene, acetic acid, ethanol, dimethylamine, and toluene) [92]. The good performance of this PWG-based sensor was attributed to its superior ability to detect changes in its effective refractive index due to VOC interaction through evanescent field coupling. ...
Exposure to volatile organic compounds (VOCs) can result in serious effects on human health. The detection and identification of VOCs are, therefore, important both in outdoor and indoor (whether workplace or residential) environments. The use of colorimetric and optical VOC sensing techniques is expected to offer new ways to overcome the many limitations of traditional gas sensors. In this work, a classification of colorimetric and optical sensing devices was performed with respect to the sensing mechanisms, principles, and sensing materials for common VOCs, including alcohols, aldehydes, alkenes, aromatic compounds, halogenated VOCs, ketones, and polycyclic aromatic hydrocarbons. The performances of these approaches were also evaluated in terms of sensitivity relative to other available methods. Furthermore, this paper offers an extensive review of recent progresses in this area with a discussion of future challenges associated with the expansion of colorimetric/optical techniques.
... Due to the adverse effects of volatile organic solvents on humans, there has been an increasing need for developing new sensitive, low-cost and portable systems, which can respond in real time, for monitoring trace levels of volatiles in various environmental and industrial applications. Currently, there are some promising low-cost devices, with high sensitivity and low dimensionality known as chemical sensors, which are based on capacitive effects [8,9], resistive effects [10,11], optical fibers [12,13], field effect transistors (FETs) [14,15], surface acoustic waves (SAWs) [16,17] and quartz crystal microbalances (QCM) [18,19]. Among the SAW sensors, the Love-wave devices have generated great interest as gas sensors due to their potential to confine the wave energy in a thin guiding layer, provided that the velocity of the acoustic wave in the guiding layer is slower than that in the substrate, obtaining in this way a very high mass sensitivity. ...
Love-wave gas sensors based on surface functionalized iron oxide nanoparticles has been developed in this research. Amino-terminated iron oxide nanoparticles were deposited, by a spin coating technique, onto the surface of Love-wave sensors, as a very reproducible gas-sensing layer. The gases tested were organic solvents, such as butanol, isopropanol, toluene and xylene, for a wide and low concentration range, obtaining great responses, fast response times of a few minutes (the time at which the device produced a signal change equal to 90%), good reproducibilities, and different responses for each detected solvent. The estimated limits of detection obtained have been very low for each detected compound, about 1 ppm for butanol, 12 ppm for isopropanol, 3 ppm for toluene and 0.5 ppm for xylene. Therefore, it is demonstrated that this type of acoustic wave sensor, with surface amino-functionalized nanoparticles, is a good alternative to those ones functionalized with metal nanoparticles, which result very expensive sensors to achieve worse results.
... A band-pass filter had been developed by coupling double long-period fiber gratings (LPG) with a core mode blocker or a hollow fiber [35][36][37]. Different optical fiber sensing devices for detecting different variables have been developed, such as displacement sensors, strain sensors, pressure sensors and volatile organic compound gas sensors [38][39][40][41][42][43]. ...
A novel optical fiber array-type of sensing instrument with temperature compensation for real-time detection was developed to measure oxygen, carbon dioxide, and ammonia simultaneously. The proposed instrument is multi-sensing array integrated with real-time measurement module for portable applications. The sensing optical fibers were etched and polished before coating to increase sensitivities. The ammonia and temperature sensors were each composed of a dye-coated single-mode fiber with constructing a fiber Bragg grating and a long-period filter grating for detecting light intensity. Both carbon dioxide and oxygen sensing structures use multimode fibers where 1-hydroxy-3,6,8-pyrene trisulfonic acid trisodium salt is coated for carbon dioxide sensing and Tris(2,2′-bipyridyl) dichlororuthenium(II) hexahydrate and Tris(bipyridine)ruthenium(II) chloride are coated for oxygen sensing. Gas-induced fluorescent light intensity variation was applied to detect gas concentration. The portable gas sensing array was set up by integrating with photo-electronic measurement modules and a human-machine interface to detect gases in real time. The measured data have been processed using piecewise-linear method. The sensitivity of the oxygen sensor were 1.54%/V and 9.62%/V for concentrations less than 1.5% and for concentrations between 1.5% and 6%, respectively. The sensitivity of the carbon dioxide sensor were 8.33%/V and 9.62%/V for concentrations less than 2% and for concentrations between 2% and 5%, respectively. For the ammonia sensor, the sensitivity was 27.78%/V, while ammonia concentration was less than 2%.
... Side-polishing method was also used in a sensitive DNA biosensor based on a long period grating (LPG) to enhance the interaction between the fundamental fiber core mode and the external medium for high sensitivity [17]. On most occasions, removed cladding makes the RI (refractive index) much more sensitive to external medium or evanescent field, thus the side polished technique is preferred to be a RI-based sensor [18][19][20]. ...
... Side-polishing method was also used in a sensitive DNA biosensor based on a long period grating (LPG) to enhance the interaction between the fundamental fiber core mode and the external medium for high sensitivity [17]. On most occasions, removed cladding makes the RI (refractive index) much more sensitive to external medium or evanescent field, thus the side polished technique is preferred to be a RI-based sensor [18][19][20]. Side-polished fibers have an interesting D-shaped structure in which the cladding is laterally polished to a small distance to the core, which can increase the sensitivity of fiber sensors. To enhance the performance of hydrogen sensors in sensitivity, a new type of hydrogen sensor based on a D-shaped fiber Bragg grating coated with a thin palladium (Pd) and silver (Ag) alloy film is proposed in the article. ...
Dissolved hydrogen is a symbol gas decomposed by power transformer oil for electrical faults such as overheat or partial discharges. A novel D-shaped fiber Bragg grating (D-FBG) sensor is herein proposed and was fabricated with magnetron sputtering to measure the dissolved hydrogen concentration in power transformer oil in this paper. Different from the RI (refractive index)-based effect, D-FBG in this case is sensitive to curvature caused by stress from sensing coating, leading to Bragg wavelength shifts accordingly. The relationship between the D-FBG wavelength shift and dissolved hydrogen concentration in oil was measured experimentally in the laboratory. The detected sensitivity could be as high as 1.96 μL/L at every 1-pm wavelength shift. The results proved that a simple, polished FBG-based hydrogen sensor provides a linear measuring characteristic in the range of low hydrogen concentrations in transformer oil. Moreover, the stable hydrogen sensing performance was investigated by X-ray diffraction analysis.
... In general, FOCS for VOCs are based on indirect sensing schemes, in which the color, refractive index or fluorescence of an immobilized indicator probe or an optically detectable label is monitored [1][2][3][4]. This field is an active area of research that includes advanced methods of interrogation [5][6][7] and the use of advanced polymers and nanomaterials [8][9][10][11]. These sensitive thin films change their optical properties upon interaction with the analyte, leading to a change in the reflected light, especially in the case of the fiber-optic reflectance sensors (FORS) [10]. ...
