Uma Sampathkumaran

Fluorescent-Dye-Doped Sol−Gel Sensor for Highly Sensitive Carbon Dioxide Gas Detection below Atmospheric Concentrations

Optical fluorescence sol-gel sensors have been developed for the detection of carbon dioxide gas in the 0.03-30% range with a detection limit of 0.008% (or 80 ppm) and a quantitation limit of 0.02% (or 200 ppm) CO(2). Sol-gels were spin-coated on glass slides to create an organically modified silica-doped matrix with the 1-hydroxypyrene-3,6,8-trisulfonate (HPTS) fluorescent indicator. The luminescence intensity of the HPTS indicator (513 nm) is quenched by CO(2), which protonates the anionic form of HPTS. An ion pair technique was used to incorporate the lipophilic dye into the hydrophilic sol-gel matrix. TiO(2) particles (<5 microm diameter) were added to induce Mie scattering and increase the incident light interaction with the sensing film, thus increasing the signal-to-noise ratio. Moisture-proof overcoatings have been used to maintain a constant level of water inside the sensor films. The optical sensors are inexpensive to prepare and can be easily coupled to fiber optics for remote sensing capabilities. A fiber-optic bundle was used for the gas detection and shown to work as part of a multianalyte platform for simultaneous detection of multiple analytes. The studies reported here resulted in the development of sol-gel optical fluorescent sensors for CO(2) gas with sensitivity below that in the atmosphere (ca. 387 ppm). These sensors are a complementary approach to current FT-IR measurements for real-time carbon dioxide detection in environmental applications.

ULTRASENSITIVE AND ACCURATE ALZHEIMER’S DISEASE DIAGNOSTICS: FROM BENCH TO BEDSIDE

Dementia, Institute Born-Bunge, Antwerp, Belgium; Neurodegenerative Brain Diseases Group, Center for Molecular Neurology, VIB, Antwerp, Belgium; Reference Center for Biological Markers of Dementia, Laboratory of Neurochemistry and Behavior, Institute Born-Bunge, University of Antwerp, Antwerp, Belgium; Institute Born-Bunge, Wilrijk, Belgium; Neurodegenerative Brain Diseases Group, VIB-UAntwerp Center for Molecular Neurology, Antwerp, Belgium; Laboratory of Neurobiology, Institute Born-Bunge, University of Antwerp, Antwerp, Belgium; Institute Born-Bunge, University of Antwerp, Antwerp, Belgium; VU University Medical Center, Amsterdam, Netherlands; Reference Center for Biological Markers of Dementia, Institute Born-Bunge, University of Antwerp, Antwerp, Belgium. Contact e-mail: e.willemse@vumc.nl

Protective Ceramic Coatings for Solid Oxide Fuel Cell (SOFC) Balance-of-Plant Components

Solid oxide fuel cells (SOFCs) have the potential to meet the growing need for electrical power generation if the cost per megawatt can be further reduced. Currently, SOFC stacks are replaced too frequently to be cost competitive. SOFC service life can be extended by preventing chromium- (Cr-) bearing species from evaporating from the interior surfaces of balance of plant (BOP) components and poisoning the cathode to increase the lifetime. We have developed yttria-stabilized zirconia (YSZ) and aluminum oxide- (Al2O3-) modified sol-gel paints or inks for coating BOP components. 430 stainless steel (430SS) substrates with three surface conditions were coated with the 0.8–1.5 µm thick YSZ and Al2O3 paints. The coated 430SS samples were tested for thermal cycling resistance, thermal soak, and Cr evaporation. Thermal soak and thermal cycling test results show promise for the YSZ-coated 430SS substrates. The Cr evaporation test of a coated substrate showed a 51% reduction in Cr generation, when compared with a bare substrate.

Excitation light leakage suppression using temperature sensitive fluorescent agents

Fluorescence tomography is a non invasive, non ionizing imaging technique able to provide a 3D distribution of fluorescent agents within thick highly scattering mediums, using low cost instrumentation. However, its low spatial resolution due to undetermined and ill-posed nature of its inverse problem has delayed its integration into the clinical settings. In addition, the quality of the fluorescence tomography images is degraded due to the excitation light leakage contaminating the fluorescence measurements. This excitation light leakage results from the excitation photons that cannot be blocked by the fluorescence filters. In this contribution, we present a new method to remove this excitation light leakage noise based on the use of a temperature sensitive fluorescence agents. By performing different sets of measurements using this temperature sensitive agents at multiple temperatures, the excitation light leakage can be estimated and then removed from the measured fluorescence signals . The results obtained using this technique demonstrate its potential for use in in-vivo small animal imaging.

Temperature-modulated fluorescence tomography: modulating tissue temperature using HIFU for high-resolution in vivo fluorescence tomography

Low spatial resolution due to strong tissue scattering is one of the main barriers that prevent the wide-spread use of fluorescence tomography. To overcome this limitation, we previously demonstrated a new technique, temperature modulated fluorescence tomography (TM-FT), which relies on key elements: temperature sensitive ICG loaded pluronic nanocapsules and high intensity focused ultrasound (HIFU), to combine the sensitivity of fluorescence imaging with focused ultrasound resolution. While conventional fluorescence tomography measurements are acquired, the tissue is scanned by a HIFU beam and irradiated to produce a local hot spot, in which the temperature increases nearly 5K. The fluorescence emission signal measured by the optical detectors varies drastically when the hot spot overlays onto the location of the temperature dependent nanocapsules. The small size of the focal spot (~1.4 mm) up to a depth of 6 cm, allows imaging the distribution of these temperature sensitive agents with not only high spatial resolution but also high quantitative accuracy in deep tissue using a proper image reconstruction algorithm. Previously we have demonstrated this technique with a phantom study with nanocapsules sensitive to 20-25°C range. In this work, we will show the first nanocapsules optimized for in vivo animal imaging.

A combined HIFU-Fluorescence Tomography high-resolution imaging technique using temperature-modulated thermodots

We present a high-resolution fluorescence imaging technique based on the use of in-vivo temperature sensitive ICG loaded pluronic nanocapsules and the synergistic combination of two imaging techniques: Fluorescence Tomography (FT) and High Intensity Focused Ultrasound (HIFU).

Optical Sensor for Unambiguous Trace Hydrogen Detection in the Presence of Oxygen

Next generation crewed spacecraft are expected to produce oxygen, using on-board oxygen generation systems (water electrolysis for example). H2 and O2 being products of electrolysis, a safety sensor for trace hydrogen gas detection is required in a moist O2 gas stream. Currently H2 is vented out of the spacecraft, whereas O2 is bled into the ventilation loop of the spacecraft. Early detection of trace H2 levels and warning of H2 buildup would be critical for ensuring mission and crew safety. To meet this need, InnoSense LLC investigated sensors that can detect the presence of hydrogen in 100% oxygen background unambiguously. The hydrogen sensor design utilizes colorimetric indicators immobilized in an organically modified silicate (ORMOSIL) matrix deposited onto glass substrates. The temperature sensor uses a luminophore immobilized in an ORMOSIL matrix which is further encapsulated by an oxygen barrier layer. The hydrogen and temperature indicating materials are sensitive, selective, and respond to the presence of analytes through absorbanceor luminescence-based pathways. Changes in the luminescence/absorbance properties of the coated substrates are directly related to changes in the analytes of interest. We successfully screened hydrogen-sensing formulations with a working model of a multianalyte optical sensor that detects 25 ppm of H2 in N2 background, 100 ppm H2 in dry 90% O2 and 1000 ppm in moist 90% O2 background. We also demonstrated temperature-sensing capabilities with the optical temperature sensor in the range of 23–100 °C. The optoelectronic design includes feedback loop circuitry for self-referencing and drift-free sensor performance. Electronic temperature and humidity sensors are included for temperatureand humidity-compensated calibration capability. The multi-analyte optical sensor array (MOSA) platform enables the expansion of detected species to include a trace O2 sensor in hydrogen background or other relevant gas phase species. The development of this sensor has broad implications for use in monitoring the air quality of enclosed environments such as aircraft, buildings, submarines and automobiles.

Quenchometric Strategies for Determining O 2 in the 99- 100% Region

We describe a luminescence-based quenchometric sensor arrays that exploit tailored class II xerogels doped with a luminophore (tris(4,7-diphenyl-1,10phenanthroline)ruthenium(II) (Ru(dpp) 3) 2+ ), Pt(II) meso-tetra( N-methyl-4pyridyl)porphyrin tetrachloride (PtTMP), or Pt(II) octaethylporphine (PtOEP)) in concert with an artificial neural network. The xerogel response to O 2 is tuned by choice of luminophore dnd the xerogel composition. The xerogel composition is controlled by changing the sol precursors and their mole fractions. A three layer multilayer perceptron network with backward error propagation was used for training. The collective microarray platform exhibited the ability to discriminate O 2 concentrations from 0.05% to 100% O 2; in the 99-100% region the resolution is 0.2 % O2.

Miniaturized Multi-Analyte Sensor for Monitoring Major Atmospheric Constituents in Space Cabin Air

The Major Constituent Analyzer (MCA) is a mass spectrometer-based instrument that is currently used to continuously monitor the partial pressure of six major atmospheric constituents (MACs), namely, nitrogen (N2), oxygen (O2), hydrogen (H2), carbon dioxide (CO2), methane and water vapor on-board the International Space Station (ISS). The operating life of the mass spectrometer is limited by the operating life of the ion pump and ion source filaments to about 1 to 2 years. Water absorption/desorption in the lines renders reliable measurement of water vapor a challenge. This system is accurate for MACs, but its mass and bulk may not be conducive for next generation spacecrafts sought by the National Aeronautics and Space Administration (NASA) agency. To meet this need, a multi-analyte optical sensor array (MOSA) has been constructed and its performance evaluated to monitor MACs. The MOSA design utilizes organically modified silicates and polymer materials to immobilize chemical indicators onto glass substrates. The chemical indicators are sensitive, selective, and respond to the presence of analytes through luminescence- or absorbance-based pathways. Changes in the luminescence/absorbance properties of the coated substrates are directly related to changes in the analytes of interest. The sensor demonstrates a wide dynamic detection range for each analyte (0–40% O2, 0.01–3% CO2, 20–80% relative humidity (RH)) and is able to resolve changes of ±0.1% O2, ±10 ppm CO2, and ± 5% RH. The optoelectronic design includes a feedback loop circuitry for selfreferencing and drift-free sensor performance. The development of this sensor has broad implications for use in monitoring the air quality of enclosed environments such as aircraft, buildings, submarines and automobiles.

All-Optical Fuel Leak Detector for Monomethylhydrazine

Hydrazine-based fuels are commonly used in many missiles, spacecraft and space launch vehicles. These chemicals are extremely toxic, highly energetic, and consequentially very hazardous. Currently, monomethyl hydrazine (MMH) is considered to be the predominant fuel for spontaneous ignition. However, time-weighted average (TWA) MMH concentrations as low as 10 ppb represent a significant health hazard to people. Therefore, monitoring leakage of these chemicals in ambient air is highly important. InnoSense LLC’s (ISL) all-optical leak detector can be calibrated to detect leaks in the parts-permillion to parts-per-billion range. ISL’s innovative sensor device incorporates a self-referenced, fiber-optics-based sensor platform for detecting MMH under extreme temperature conditions (-46C to +71C). This is a significant technical achievement for InnoSense LLC—a challenge that has defeated some alternative sensor technologies.