A smart Oxygen Cuvette is developed by coating the inner surface of a cuvette with oxygen sensitive thin film material.
The coating is glass like sol-gel based sensor that has an embedded ruthenium compound in the glass film. The
fluorescence of the ruthenium is quenched depending on the oxygen level. Ocean Optics phase fluorometer, NeoFox is
used to measure this rate of fluorescence quenching and computes it for the amount of oxygen present. Multimode
optical fibers are used for transportation of light from an LED source to cuvette and from cuvette to phase fluorometer.
This new oxygen sensing system yields an inexpensive solution for monitoring the dissolved oxygen in samples for
biological and medical applications. In addition to desktop fluorometers, smart oxygen cuvettes can be used with the
Ocean Optics handheld Fluorometers, NeoFox Sport. The Smart Oxygen Cuvettes provide a resolution of 4PPB units, an
accuracy of less than 5% of the reading, and 90% response in less than 10 seconds.
A Smart pH Cuvette is developed by coating the inner surface with pH sensitive thin film. The coating is a hydroscopic
sol-gel material doped with colorimetric pH indicator dye sensitive to the pH of analyte solutions in biological range.
Ocean optics miniaturized spectrometers are used for signal detection and analysis, along with multimode optical fibers.
This new pH sensing arrangement yields an inexpensive solution for monitoring the pH of samples for biological
applications. The Smart pH Cuvettes provide a resolution of 0.01 pH units, an accuracy of 1% of the reading, and 90%
response in less than 10 seconds.
A Nanoporous glass matrix is developed to encapsulate molecular probes for monitoring important biological
parameters such as DO. The hydrophobic nanoporous host matrix is designed and fabricated using room temperature
sol gel technique. The doped sol gel is then coated on biocompatible self adhesive patches or directly coated on the
biocontainers. We demonstrate the application of this technique in non-invasive monitoring DO as well as oxygen
partial pressure in a closed fermentation process as well as in a cell culture plate during bacterial growth. Dynamic
response of sensor, sensitivity and accuracy is also demonstrated in this paper.
Surface-enhanced Raman spectroscopy (SERS) promises to be one of the most sensitive methods for chemical detection. Unfortunately, the inability of SERS to perform quantitative chemical analysis has slowed its general use in laboratories. This is largely due to the difficulty of manufacturing either active surfaces that yield reproducible enhancements, or surfaces that are capable of reversible chemical adsorption, or both. In an effort to meet this need, we have developed metal-doped sol-gels that provide surface-enhancement of Raman scattering. The porous silica network offers a unique environment for stabilizing SER active metal particles and the high surface area increases the interaction between the analyte and metal particles. This eliminates the need to concentrate the analyte on the surface by evaporating the solvent. The sol-gel is easily coated on a variety of surfaces, such as fiber optics, glass slides, or glass tubing, and can be designed into sample flow systems. Here we present the development of both gold- and silver-doped sol-gels, which have been used to coat the inside walls of glass sample vials for SERS applications. The performance of the metal-doped sol-gels was evaluated using p-aminobenzoic acid, to establish enhancement factors, detection limits, dynamic response range, reversibility, reproducibility, and suitability to commercial spectrometers. Measurements of trace chemicals, such as adenine and cocaine, are also presented.
A new fiber optic sensor for monitoring pH made by doping of fluorescent dyes in a sol-gel matrix is demonstrated. The indicator, 5-(and6)-carboxy-2'7'-dichlorofluorescein (CDCF), has a lower average pKa than fluorescein due to a chloride functional modification. The absorption and fluorescence spectra of the immobilized dye at various pH levels show that the indicator is sensitive over a wide pH range. Porous sol-gel coatings are used to make the probes, which are incorporated into a bifurcated fiber optic sensor. The entire absorption and fluorescence spectra are continuously monitored using a miniature fiber optic spectrophotometer. The most responsive area of the fluorescence spectrum is selected and is referenced to a point which is insensitive to pH, so that any changes due to environmental effects and fluctuations in the light source are taken into account. Two approaches for referencing are shown, one involving the back-reflected light from the excitation source, and another utilizing the co-doping of the sol-gel with a second fluorescent dye with the same absorption characteristic as CDCF but which is insensitive to pH and fluoresces at a different wavelength.
A comprehensive study of the luminescence quenching behavior of ruthenium(II)-tris-4,7-diphenyl-1,10-phenanthroline perchlorate dissolved in various sol-gel matrices was performed. Thin films of submicron thickness were formed by depositing tetraethyl orthosilicate (TEOS) gel solutions, organically modified with methyltrimethoxysilane (MTMS), onto glass slides using conventional spin-coating methods. Systematic changes in composition were conducted to examine the structural properties of the sol-gel silicate thin films for possible use in fluorescence sensing applications. Luminescence quenching in the presence of oxygen was analyzed as a function of varying sol-gel composition. Modeling techniques were employed to determine the best exponential decay curve fit of different thin film samples. The degree of luminescence quenching was found to be greatest in the polar TEOS thin films. However, whereas cracking was prevalent in the pure TEOS thin films, certain levels of organic modification with non-polar MTMS prevented cracking while maintaining a high degree of fluorescence quenching. These organically modified sol-gel thin films appear to be the most suitable for fluorescence-based oxygen sensing applications.
Organically modified silicate (ormosil) sol-gel thin films have many advantages over their inorganic sol-gel and polymeric counterparts for sensing applications. The addition of methyltrimethoxysilane (MTMS) to tetraethyl orthosilicate (TEOS)-based gels creates a film with much greater hydrophobicity and less cracking due to replacement of hydroxyl groups by non-hydrolyzable methyl groups. The more hydrophobic thin film is advantageous in oxygen sensing applications, since it allows only gaseous interaction with the sensing element, and liquid infiltration into the gel is minimized. Organic modification of the gels is found to increase the degree of fluorescence quenching in dip-coated films, as evidenced by fluorescence lifetime measurements, due to the more open structure of the ormosil. However, hydrophilicity can still be obtained in the ormosil thin films by adding smaller amounts of MTMS and greater amounts of TEOS. This creates a partially hydrophilic film which still maintains a low degree of cracking due to the MTMS addition. Hydrophilic films are much desired in hydrogen sulfide and carbon dioxide sensing applications, where liquid interaction with the gel matrix itself is necessary for proper protonation and deprotonation reactions. While TEOS-based spin-coated thin films have been shown to quench more poorly with additions of MTMS, it is found that low levels of organic modification will prevent cracking of the spun films while still maintaining a very high degree of fluorescence quenching. Hence, ormosil thin films have strong potential in a wide array of chemical, biochemical, and environmental sensing applications.
Two fiber optic oxygen sensor designs were demonstrated by sol-gel coatings doped with an organo-metallic complex, ruthenium (II) tris-4,7-diphenyl-1,10-phenanthroline. The first design implemented a porous optical fiber coated with sol-gel that showed high sensitivity (less than 1 ppm) towards oxygen gas and a dynamic range up to 1% oxygen. The second optical sensor was based on a collimator device which involved a sol-gel film that was spin coated onto a silica glass disk. Compared to the porous fiber approach, a faster response time and lower oxygen gas sensitivity were determined for this sensor configuration. According the lifetime decay behavior of a sol-gel spin coating, the luminescence decay of the ruthenium complex followed a single exponential decay in nitrogen and air. Also, the spin coated sample showed a greater degree of quenching according to the Stern-Volmer ratio, at greater oxygen concentrations than the ratio calculated for the monolithic film. Analysis of the lifetime decay behavior of the different forming methods revealed that the micro-structure of the gel was dependent upon the type of sol-gel deposition. In this case, spin coated gels resulted in a denser coating than the monolithic film. As a result, these differences in the sol- gel micro-structure were used to discuss the different behavior of the collimator sensor with respect to the porous fiber oxygen sensor.
Fluorescence decay of the well-known fluorophore, ruthenium (II) 4,7-diphenyl-1,10-phenanthroline perchlorate, has been studied in a series of sol-gel matrices, including non-polar methyltrimethoxysilane (MTMS) and highly polar tetraethylorthosilicate (TEOS)-based gels. Systematic changes in composition and processing techniques have been fabricated to examine the structural properties of sol-gel silicates for possible oxygen sensor supports. Measurements were performed using both brush-coated and spin-coated sol- gel thin films as well as sol-gel monoliths. Gel compositions consisted of either 100% MTMS, 100% TEOS, or a 1:1 molar ratio of MTMS to TEOS. Quenching behavior was analyzed as a function of varying sol-gel composition, processing technique (spin-coated, brush-coated, etc.), and fluorophore concentration. The use of modeling techniques were employed to enable determination of possible singe or multi-exponential decay behavior in different sol-gel samples. Causes for the variations in quenching properties as a function of gel composition and processing technique were explained by a two-domain model. In addition, phase fluorimetric analysis was conducted on all doped sol-gel samples to determine the change in phase between the quenched and unquenched states of the films. Direct experimental phase data was compared to phase results calculated from the experimental lifetime data in order to examine the accuracy of the luminescence decay times. Possible design of sol-gel supports for oxygen sensors was also discussed.
Three optically active organic indicators were evaluated for monitoring O2, dissolved H2S and CO. By combining a sol-gel coating with porous fiber technology, a fluorescence sensor was developed for oxygen concentrations less than 1 ppm. A second sol-gel material also possessing fluorescence properties was examined for possible H2S sensing applications. In this instance, the fluorescence of thionin-doped, sol-gel film was quenched upon exposure to ppm-levels of dissolved H2S. Finally, preliminary results concerning the advancement of a potential CO sensor were initialized by directly absorbing the organometallic indicator onto a porous fiber substrate. Even though the minimum sensitivity was a few percent, these results were encouraging since the complex responded reversibly to CO.
Sol-gel materials were developed for potential fiber optic applications as films for detecting dissolved H2S and H2S vapor. Modification of the optical properties of gels were recognized by simply changing a processing parameter such as the type of catalyst of the introduction of a second precursor. Other properties such as chemical durability and photostability were also evaluated. Finally, the fluorescence quenching of thionin doped gels by dissolved H2S revealed a sensitivity and reversibility in the parts-per-billion regime. After performing these preliminary steps to assess the gel's integrity, the thionin doped gel is now read for H2S monitoring.
An intrinsic fiber optic environmental sensor has been developed for on-line monitoring of oxygen gas and dissolved oxygen (DO). In this O2/DO sensor, a highly stable compound [Tris-(4,7-Diphenyl-1, 10-phenanthroline) Ruthenium (II) complex] is synthesized and selected as a chemical indicator for oxygen. A hybrid matrix is designed by a sol-gel process and used as a stable substrate for the immobilization of Ru compound. The microporous nature of the nondensified sol-gel coating, in which the photochemical dye is immobilized, provides a unique local structure that is environmentally stable and immune to photochemical bleaching and chemical leaching. The doped hybrid material is then coated on a porous optical fiber substrate used as the sensing component. The oxygen penetrates into the interconnective porous core and interacts with the immobilized Ru compound in which in-line dynamic luminescence quenching takes place. The use of Ru(ph2phen)3[2+] as a highly stable, reagent sensing indicator and also the use of the sol-gel coating technique for the immobilization and incorporation of Ru compound to porous core optical fibers have resulted in the development of an intrinsic O2/DO sensor with high sensitivity, reproducibility, and long-term stability.
The polarity of the silica cage has been investigated by entrapping organic dyes in a silica gel. pH dyes of bromocresol purple and bromocresol green were selected for this study. The influence of pH on the polarity of the silica cage was determined by measuring the spectral shift of the dye. The pH dye- impregnated silica films show a red-shift in an acidic environment and a blue shift in basic environment, compared to those dissolved in water. This implies that the polarity of a silica cage varies after being treated by different pH solutions. The cage shows higher polarity in a basic solution than in an acidic solution.
The effect of high temperature aqueous solutions of various pH values on the mechanical properties of polymer coated optical fibers of an aluminum fluoride-based composition are examined. It was found that such fibers retain much more strength when aged in these aqueous environments than fibers of the more common zirconium fluoride-based composition. The aging is not affected by pH unless the fiber is under stress, in which case a low pH solution decreases the time to failure of the fiber. In static fatigue, the time to failure of the aluminum fluoride-based fibers is 20 times greater than that of the zirconium fluoride-based fibers.
Spectral attenuation measurements were obtained on some JR transmitting waveguides to
evaluate their applicability for remote sensing and laser power delivery. Since there is such a wide
variety of applications for fiber optics in these areas, it is important to evaluate materials with various
physical and optical properties. Three categories of waveguides where analyzed: glass, crystalline, and
hollow tubes. A fluoroaluminate glass optical fiber was fabricated and the attenuation was considerably
higher (102103 times higher) than the more common ZBLAN fluoride optical fibers. A Te-Se-Br glass
optical fiber was evaluated and it exhibited an extended JR edge to approximately 14 rim. Attenuation
measurements were conducted on single crystal sapphire, silicon, KRS-13, and KBr core/KC1 clad optical
fibers. The spectral characteristics of alumina, silica glass, and mullite hollow waveguides were also
determined, and all measurements were obtained using a Fourier Transform Infrared Spectrometer.
A power delivery system capable of delivering high energy densities of
infrared radiation at 2.94 tm is required for the application of the Erbium-YAG laser
in the medical industry. Conventional silica fibers have high intrinsic absorption
coefficients in this spectral region, making them unsuitable for this application.
Several alternative fibers were evaluated as candidates for delivering laser radiation
at this wavelength, including single crystal fibers of sapphire and silicon,
polycrystalline fibers of KRS-13, and glass fibers of fluorozirconate and
fluoroaluminate compositions. For each of these, damage thresholds, fiber
attenuation coefficients and maximum deliverable energies were determined.
Commercially available fluorozirconate fibers proved to be the most promising
candidates for this application, with a loss of under 40 dB/km and a damage threshold
of over 1000 J/ cm2.