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Optical chemical sensors : design and applications
Aleksandra Lobnik, Matejka Turel, Špela Korent Urek, 2012, independent scientific component part or a chapter in a monograph

Keywords: optical chemical sensors, opt(r)odes, chemical sensors
Published: 01.06.2012; Views: 864; Downloads: 6
URL Full text (0,00 KB)

Sol-gel-based optical sensor for the detection of aqueous amines
Špela Korent Urek, Aleksandra Lobnik, Gerhard J. Mohr, 2007, original scientific article

Abstract: We present an optical sensor for the detection of aqueous amines obtained by incorporating chromoionophore XV (ETHT 4001) into sol-gel thin films. Acid- and base-catalyzed sol-gel processes were studied to prepare stable ormosil layers using various amounts of organically modified sol-gel precursor such asmethyltriethoxysilane (MTriEOS). The sensor layers were coated with a protective layer of microporous white polytetrafluoroethylene (PTFE) in order to prevent interference from ions and ambient light. The measurements were carried out in a flow-through cell in the reflection mode. Acid-catalyzed ormosil layers (pH 1) based on the copolymerization of tetraethoxysilane (TEOS) and MTriEOS did not show any change in signal upon exposure to aqueous amine solutions, while base-catalyzed sensor layers (pH 3 and 13) showed significant changes in signal. The response time (t100) for the base-catalyzedsensor layer L3 (pH 13) upon exposure to different solutions containing 0-608 mmol L-1 aqueous propylamine was 20-30 s, the regeneration time was 70 s and the detection limit was 0.1 mmol L-1. The sensor response was reproducible and reversible. The porous ormosil layers permit dry sensor storage conditions.
Keywords: analytical chemistry, optical sensors, sol-gel technology, determination of amines, fluorimetry
Published: 01.06.2012; Views: 1252; Downloads: 5
URL Full text (0,00 KB)

Characterisation of an optical sensor membrane based on the metal ion indication Pyrocatechol Violet
Ivana Murković Steinberg, Aleksandra Lobnik, Otto S. Wolfbeis, 2003, original scientific article

Abstract: A non-specific photometric metal ion indicator Pyrocatechol Violet (PV) was tested for its potential use in a metal-sensitive optrode membrane. The water soluble indicator was lipophilised in the form of an ion pair with tetraoctylammonium cation (TOA), and subsequently immobilised in a plasticised PVC membrane. The spectral response of the membrane in the presence of various transition metal ions was studied. It was found that the ability of PV to form complexes with metal ions significantly reduced following immobilisation, with the exception of Cu(II). A number of factors responsible for the improved selectivity and high sensitivity of immobilised PV towards Cu(II) were identified. Amongst those, the most important is the presence of quaternary ammonium salt in the membrane which induced a significant bathochromic shift of the PV-Cu(II) chelate absorption maximum, as well as the intensification of the chelate absorption band. The membrane responds to Cu(II) irreversibly by changing colour from yellow to green (absorption maximum at 740 nm), and typically, an exposure time of 10 min enables the determination of Cu(II) in the 1-100 M range. A comparison of selectivity and sensitivity characteristics between the water soluble form of the indicator and the immobilised form was performed, and the effects of pH and lipophilic surfactant additives on the response mechanism are discussed.
Keywords: optical sensors, sensor membrane, PVC membrane, photometric metal ion indicators, metal-sensitive optrode membrane, lipophilic ion pairs
Published: 01.06.2012; Views: 748; Downloads: 9
URL Full text (0,00 KB)

Spin-coating for optical-oxigen-sensor preparation
Polona Brglez, Andrej Holobar, Aleksandra Pivec, Mitja Kolar, 2014, original scientific article

Abstract: Thin-film oxygen sensors were prepared using the spin-coating technique, where a tris (4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dichloride complex (RuDPP) in various solvents and silicones deposited on different substrates was used for the sensor production. By changing the spin-coating set-up parameters, homogeneous sensor coatings and the optimum sensor response to oxygen were studied – the sensors were exposed to various concentrations of oxygen within the range from 0% to 100 %. During the presented study, the optimum results were obtained when a 150 µL of sensor solution was applied to a Dataline foil using silicone E4 and a chloroform solvent. A spin coater with the following three rotation stages was used: 750/700 r/min for 3 s, 300 r/min for 3 s and 150 r/min for 4 s. The spin-coating technique has several benefits: it is fast, easy to use and appropriate for low-volume operations. It allows modifications and preparations of several sensor series using the minimum reagent consumption. However, the disadvantage of this technique also has to be mentioned, namely, an uneven film thickness in the radial direction. The film thickness mainly depends on the experimental set-up (volume, rotation time and speed, solvent viscosity and evaporation). Spin coating as an alternative and very flexible technique for an oxygen-sensor preparation is suggested for the laboratory-scale work, where the majority of experimental data could be used when other new coating methods are also researched and implemented.
Keywords: optical sensors, spin coating, oxigen
Published: 21.12.2015; Views: 441; Downloads: 9
.pdf Full text (254,63 KB)

Fiber-optic sensors for measurements of torsion, twist and rotation
Vedran Budinski, Denis Đonlagić, 2017, review article

Abstract: Optical measurement of mechanical parameters is gaining significant commercial interest in different industry sectors. Torsion, twist and rotation are among the very frequently measured mechanical parameters. Recently, twist/torsion/rotation sensors have become a topic of intense fiber-optic sensor research. Various sensing concepts have been reported. Many of those have different properties and performances, and many of them still need to be proven in out-of-the laboratory use. This paper provides an overview of basic approaches and a review of current state-of-the-art in fiber optic sensors for measurements of torsion, twist and/or rotation.
Keywords: fiber optic sensors, twist sensors, rotation sensors, circular birefringence, linear birefringence, FBG, polarization, optical fibers, Fiber Bragg Gratings
Published: 22.06.2017; Views: 133; Downloads: 11
.pdf Full text (8,96 MB)

Monitoring the evaporation of fluids from fiber-optic micro-cell cavities
Eyal Preter, Borut Preložnik, Vlada Artel, Chaim Sukenik, Denis Đonlagić, Avi Zadok, 2013, original scientific article

Abstract: Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in monitoring the quality of water, identificationof fuel dilutions, mobile point-of-care diagnostics, climatography and more. In this work, the fiber-optic monitoring of fluids evaporation is proposed and demonstrated. Sub-nano-liter volumes of a liquid are applied to inline fiber-optic micro-cavities. As the liquid evaporates, light is refracted out of the cavity at the receding index boundary between the fluid and the ambient surroundings. A sharp transient attenuation in the transmission of light through the cavity, by as much as 50 dB and on a sub-second time scale, is observed. Numerical models for the transmission dynamics in terms of ray-tracing and wavefront propagation are provided. Experiments show that the temporal transmission profile can distinguish between different liquids.
Keywords: fiber-optic sensors, opto-fluidics, evaporation monitoring, optical micro-cells, fiber cavities, droplet analysis
Published: 22.06.2017; Views: 70; Downloads: 15
.pdf Full text (551,58 KB)

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