Laser spectroscopy for breath analysis : towards clinical implementation

Detection and analysis of volatile compounds in exhaled breath represents an attractive tool for monitoring the metabolic status of a patient and disease diagnosis, since it is non-invasive and fast. Numerous studies have already demonstrated the benefit of breath analysis in clinical settings/applications and encouraged multidisciplinary research to reveal new insights regarding the origins, pathways, and pathophysiological roles of breath components. Many breath analysis methods are currently available to help explore these directions, ranging from mass spectrometry to laser-based spectroscopy and sensor arrays. This review presents an update of the current status of optical methods, using near and mid-infrared sources, for clinical breath gas analysis over the last decade and describes recent technological developments and their applications. The review includes: tunable diode laser absorption spectroscopy, cavity ring-down spectroscopy, integrated cavity output spectroscopy, cavity-enhanced absorption spectroscopy, photoacoustic spectroscopy, quartz-enhanced photoacoustic spectroscopy, and optical frequency comb spectroscopy. A SWOT analysis (strengths, weaknesses, opportunities, and threats) is presented that describes the laser-based techniques within the clinical framework of breath research and their appealing features for clinical use.Peer reviewe

Si:WO3 Sensors for Highly Selective Detection of Acetone for Easy Diagnosis of Diabetes by Breath Analysis

Acetone in the human breath is an important marker for noninvasive diagnosis of diabetes. Here, novel chemo-resistive detectors have been developed that allow rapid measurement of ultralow acetone concentrations (down to 20 ppb) with high signal-to-nois

Toward portable breath acetone analysis for diabetes detection

Diabetes is a lifelong condition that may cause death and seriously affects the quality of life of a rapidly growing number of individuals. Acetone is a selective breath marker for diabetes that may contribute to the monitoring of related metabolic disorder and thus simplify the management of this illness. Here, the overall performance of Si-doped WO3 nanoparticles, made by flame spray pyrolysis, as portable acetone detectors is critically reviewed focusing on the requirements for medical diagnostics. The effect of flow rate, chamber volume and acetone dissociation within the measuring chamber is discussed with respect to the calibration of the sensor response. The challenges for the fabrication of portable breath acetone sensors based on chemo-resistive detectors are underlined indicating possible solutions and novel research directions

Minimal cross-sensitivity to humidity during ethanol detection by SnO2-TiO2 solid solutions

A nanocomposite material is presented that optimally combines the excellent gas sensitivity of SnO2 and the selectivity of TiO2. Nanostructured, rutile titanium-tin oxide solid solutions up to 81.5% Ti, as determined by x-ray diffraction, are made by scalable spray combustion (flame spray pyrolysis) of organometallic precursor solutions, directly deposited and in situ annealed onto sensing electrodes in one step. Above that content, segregation of anatase TiO2 takes place. It was discovered that at low titanium contents (less than 5 Ti%), these materials exhibit higher sensitivity to ethanol vapor than pure SnO2 and, in particular, limited cross-sensitivity to relative humidity, a long standing challenge for metal oxide gas sensors. These solid solutions are aggregated nanoparticles with an enhanced presence of Ti on their surface as indicated by Raman and IR-spectroscopy. The presence of such low Ti-content in the SnO2 lattice drastically reduces the band gap of these solid solutions, as determined by UV-vis absorption, almost to that of pure TiO2. Furthermore, titania reduces the number of rooted and terminal OH species (that are correlated to the cross-sensitivity of tin oxide to water) on the particle surface as determined by IR-spectroscopy. The present material represents a new class of sensors where detection of gases and organic vapors can be accomplished without pre-treatment of the gas mixture, avoiding other semiconducting components that require more heating power and that add bulkiness to a sensing device. This is attractive in developing miniaturized sensors especially for microelectronics and medical diagnostics

Thermally Stable, Silica-Doped ε-WO3 for Sensing of Acetone in the Human Breath

Acetone in the human breath is a key marker for noninvasive diagnosis of diabetes. Here, sensing films of pure and SiO2-doped WO3 nanoparticles have been made, directly deposited and in situ annealed onto interdigitated electrodes by scalable flame aerosol technology. A unique innovation here is that these films consist of ε-WO3, a metastable phase that has a high selectivity to acetone. The effect of nontoxic Si doping on the ε-phase content and crystal and grain sizes was investigated and correlated to the acetone sensing performance of these films. The thermal stability of these materials was characterized as well, revealing a unique opportunity for reliable sensing of acetone and noninvasive diagnostics of diabetes. An optimal doping level with 10 mol % SiO2 resulted in highly sensitive and highly selective acetone sensors down to 20 ppb

Anti-Fogging Nanofibrous SiO2 and Nanostructured SiO2-TiO2 Films Made by Rapid Flame Deposition and In Situ Annealing

Transparent, pure SiO2, TiO2, and mixed silica-titania films were (stochastically) deposited directly onto glass substrates by flame spray pyrolysis of organometallic solutions (hexamethyldisiloxane or tetraethyl orthosilicate and/or titanium tetra isopropoxide in xylene) and stabilized by in situ flame annealing. Silicon dioxide films consisted of a network of interwoven nanofibers or nanowires several hundred nm long and 10-15 nm thick, as determined by microscopy. These nanowire or nanofibrous films were formed by chemical vapor deposition (surface growth) on bare glass substrates during scalable combustion of precursor solutions at ambient conditions, for the first time to our knowledge, as determined by thermophoretic sampling of the flame aerosol and microscopy. In contrast, titanium dioxide films consisted of nanoparticles 3-5 nm in diameter that were formed in the flame and deposited onto the glass substrate, resulting in highly porous, lace-like nanostructures. Mixed SiO2-TiO 2 films (40 mol % SiO2) had similar morphology to pure TiO2 films. Under normal solar radiation, all such films having a minimal thickness of about 300 nm completely prevented fogging of the glass substrates. These anti-fogging properties were attributed to inhibition of water droplet formation by such super-hydrophilic coatings as determined by wetting angle measurements. Deactivated (without UV radiation) pure TiO2 coatings lost their super-hydrophilicity and anti-fogging properties even though their wetting angle was reduced by their nanowicking. In contrast, SiO 2-TiO2 coatings exhibited the best anti-fogging performance at all conditions taking advantage of the high surface coverage by TiO2 nanoparticles and the superhydrophilic properties of SiO 2 on their surface

Highly porous TiO2 films for dye sensitized solar cells

Highly porous nanoparticle films were investigated as alternative working electrode morphology for the synthesis of dye sensitized solar cells (DSSCs). These films were rapidly assembled by flame synthesis and direct aerosol deposition of TiO2 nanoparticles with high specific surface area. Structural-functional analysis of their properties revealed that the film porosity is a key parameter greatly determining the resulting energy conversion efficiency (η). In fact, aerosol deposition at low substrate temperatures (∼100 °C) led to very high porosity (ε = 98%) and weak film cohesion. These films were easily resuspended upon immersion in the dye and/or electrolyte solutions resulting in very poor performances (η = 0.08%). In contrast, allowing for partial nanoparticle sintering by deposition at moderate temperatures (∼400 °C) decreased the film porosity from 98 to 95% leading to higher mechanical stability and partially preserving the large surface required for dye adsorption. As a result, these films had drastically higher current density (12.2 mA cm-2) and overall performances (η = 5%) representing an 8 times improvement with respect to the best reported for similar highly porous morphologies. Remarkably, their conversion efficiency decreased only slightly with increasing film thickness reaching 4.6% at 128 m. This unique attribute suggests that high film porosity may inhibit recombination losses enabling utilization of thick films with enhanced light absorption properties

Semiconductor Gas Sensors: Dry Synthesis and Application

Sense and sensitivity: Dry processes allow the rapid and scalable synthesis of nanostructured metal oxide films for use as semiconductor-based gas sensors. Dense, particulate, or porous films, with thicknesses in the nm-μm range can be prepared by the a

Ultra-rapid synthesis of highly porous and robust hierarchical ZnO films for dye sensitized solar cells

© 2016 Elsevier Ltd Dye sensitized solar cells are a promising third generation solar cell technology bearing considerable commercial potential. Here, we present the synthesis of robust, aerogel-like ZnO nanoparticle films with extremely high porosity. These film morphologies enable synthesis of stable cells with linearly increasing photocurrent up to a working-electrode thickness of 200 μm. Optimized films led to more than 100% efficiency enhancement with respect to more dense film morphologies made by wet-deposition of the same ZnO nanoparticles. These results suggest that optimization of the semiconductor-electrolyte nano-interface by a hierarchical multi-scale morphology has the potential to minimize electron-holes recombination enabling efficient thick cells with substantially higher surface area for dye absorption