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Facile Fabrication of Semiconducting Oxide Nanostructures by Direct Ink Writing of Readily Available Metal Microparticles and their application as Low Power Acetone Gas Sensors

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Abstract

In this work, a facile two-step fabrication and characterization of printed acetone sensors based on mixed semiconducting metal oxides is introduced. The devices are fabricated by Direct Ink Writing metal microparticle (MP) stripes of commercially available pure iron and copper particles onto the surface of a glass substrate, forming a bridging multi-phase semiconducting oxide net by subsequent thermal annealing. The open, highly porous bridging structures consist of heterojunctions which are interconnected via non-planar CuO/Cu2O/Cu nanowires and Fe2O3/Fe nanospikes. Morphological, vibrational, chemical and structural studies were performed to investigate the contact-forming Fe2O3–CuO nanostructures on the surface of the MPs. The power consumption and the gas sensing properties showed selectivity to acetone vapor at an operating temperature of around 300 °C with a high gas response of about 50% and the lowest operating power of around 0.26 μW to a concentration of 100 ppm of acetone vapor. The combination of the possibility of acetone vapor detection, the controllable size and geometry and their low power make these printed structures important candidates for next developments of accessible detection devices, as well as acetone vapor monitoring (even below 1 ppm). The printing of MPs in general paves the way for a new generation of printed different devices, even in “home-made” conditions, for a manifold of applications tailored by the composition and geometry of the printed MP stripes, enabled through the simplicity and versatility of the fabrication method.

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... The power consumption of gas sensor at 300 • C was only 0.26 µW, and the gas sensor showed a response of 50% to 100 ppm acetone vapor. Formation of Fe 2 O 3 /CuO heterojunctions in air and subsequent modulation of potential barriers in acetone vapor were the main reasons for acetone sensing mechanism [134]. ...
... The power consumption of gas sensor at 300 °C was only 0.26 μW, and the gas sensor showed a response of 50% to 100 ppm acetone vapor. Formation of Fe2O3/CuO heterojunctions in air and subsequent modulation of potential barriers in acetone vapor were the main reasons for acetone sensing mechanism [134]. Figure 9. (a-c) Different steps for preparation of CuO/Fe2O3 gas sensor using direct ink writing (DIW) method [134]. ...
... Formation of Fe2O3/CuO heterojunctions in air and subsequent modulation of potential barriers in acetone vapor were the main reasons for acetone sensing mechanism [134]. Figure 9. (a-c) Different steps for preparation of CuO/Fe2O3 gas sensor using direct ink writing (DIW) method [134]. Reprint permission was obtained from Elsevier. ...
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Acetone is a well-known volatile organic compound that is widely used in different industrial and domestic areas. However, it can have dangerous effects on human life and health. Thus, the realization of sensitive and selective sensors for recognition of acetone is highly important. Among different gas sensors, resistive gas sensors based on nanostructured metal oxide with high surface area, have been widely reported for successful detection of acetone gas, owing to their high sensitivity, fast dynamics, high stability, and low price. Herein, we discuss different aspects of metal oxide-based acetone gas sensors in pristine, composite, doped, and noble metal functionalized forms. Gas sensing mechanisms are also discussed. This review is an informative document for those who are working in the field of gas sensors.
... The generation of heat and its accumulation inside the batteries is often accompanied by the generation of flammable gas due to various parasitic reactions, therefore it is necessary to improve the safety of the batteries by preventing the generation of these gases. [15,17,19]. ...
... The recent huge demand towards portable devices with precise sets of properties requires cost-effective materials and new approaches to fabricate devices out of these materials [19]. Based on that, 3D-DIW devices have attracted our consideration, due to their design potentiality as shown already e.g., for new strain sensing [21] or totally electronic components [22]. ...
... Thus, the development of a class of 3D-DIW nanomaterial consisting of semiconducting oxide particles, which can detect explosive vapor leakages and indicate on necessity of rapid disconnection battery under abnormal concentrations, such as C3H6O2, C4H10O2 vapors, electrolytes containing LiTFSI and LiNO3 salts in a mixture of DOL:DME, as well as to LiPF6 salts in a mixture of EC:DMC is highly demanded. Oxide-based nanostructures, especially a combination of p and n-type conductivity (CuO and Fe2O3), TiO2 and Al2O3/CuO and CuO:Fe2O3, are highly prominent investigated mixtures for gas sensors due to their response, stability, and good sensitivity [19,[24][25][26]. ...
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Lithium-ion batteries (LIBs) still need continuous safety monitoring based on their intrinsic properties, as well as due to the increase in their sizes and device requirements. The main causes of fires and explosions in LIBs are heat leakage and the presence of highly inflammable components. Therefore, it is necessary to improve the safety of the batteries by preventing the generation of these gases and/or their early detection with sensors. The improvement of such safety sensors requires new approaches in their manufacturing. There is a growing role for research of nanostructured sensor’s durability in the field of ionizing radiation that also can induce structural changes in the LIB’s component materials, thus contributing to the elucidation of fundamental physicochemical processes; catalytic reactions or inhibitions of the chemical reactions on which the work of the sensors is based. A current method widely used in various fields, Direct Ink Writing (DIW), has been used to manufacture heterostructures of Al2O3/CuO and CuO:Fe2O3, followed by an additional ALD and thermal annealing step. The detection properties of these 3D-DIW printed heterostructures showed responses to 1,3-dioxolan (DOL), 1,2-dimethoxyethane (DME) vapors, as well as to typically used LIB electrolytes containing LiTFSI and LiNO3 salts in a mixture of DOL:DME, as well also to LiPF6 salts in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) at operating temperatures of 200 °C–350 °C with relatively high responses. The combination of the possibility to detect electrolyte vapors used in LIBs and size control by the 3D-DIW printing method makes these heterostructures extremely attractive in controlling the safety of batteries.
... In general, 3D printing, is possibly the most popular method to manufacture gas sensors, similar to ink-jet printing. In particular, this method was effectively used to fabricate a composite sensing material based on Cu and Fe microparticles whose surface was subject to a partial oxidation as a result of additional heat treatment in air [74] (Figure 4). The coating fabricated by this protocol has been characterized as rather selective to acetone vapors to yield a 50% chemiresistive response to 100 ppm of the analyte. ...
... The 3D printing has also employed other functional layers in electrochemical detectors [75], biosensors [76], photoelectrodes [77,78], photoresist printing [79], biomaterials, porous materials [80,81], flexible electronics [82], optoelectronics [83], production of drugs [84], and perovskite layers [85]. Reproduced from ref. [74]. Copyright 2020, Elsevier, Ltd. ...
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Herein, we review printing technologies which are commonly approbated at recent time in the course of fabricating gas sensors and multisensor arrays, mainly of chemiresistive type. The most important characteristics of the receptor materials, which need to be addressed in order to achieve a high efficiency of chemisensor devices, are considered. The printing technologies are comparatively analyzed with regard to, (i) the rheological properties of the employed inks representing both reagent solutions or organometallic precursors and disperse systems, (ii) the printing speed and resolution, and (iii) the thickness of the formed coatings to highlight benefits and drawbacks of the methods. Particular attention is given to protocols suitable for manufacturing single miniature devices with unique characteristics under a large-scale production of gas sensors where the receptor materials could be rather quickly tuned to modify their geometry and morphology. We address the most convenient approaches to the rapid printing single-crystal multisensor arrays at lab-on-chip paradigm with sufficiently high resolution, employing receptor layers with various chemical composition which could replace in nearest future the single-sensor units for advancing a selectivity.
... Moreover, exhaled VOCs can serve as biomarkers to assist in the non-invasive identification of various diseases. For example, acetone indicates diabetes 14,[32][33][34][35] , whereas isoprene, toluene, and acetic acid are signals of lung cancer, 31,[36][37][38] and breath testing is therefore a highly promising approach for non-invasive cancer screening 39 . VOC analysis in patient breath offers insight into the metabolic processes in the anatomy/physiology that are altered by underlying diseases 40,41 , although a detailed impression of the metabolic route leading to these molecules is still under investigation 39 . ...
... MR experiments were done using a Raman WITec Alpha300 RA spectrometer at 22C, as reported before 46 . A graphite monochromatized CuK_1 radiation (1.5405 Å) at 40 kV and 40 mA were used for the X-ray diffraction (XRD), which was carried out using a Seifert 3000 TT instrumenr, 33 and X-ray photoelectron spectroscopy (XPS) was used to measure the thickness of the TiO2/CuO thin films by using an Omicron Nano-Technology GmbH, Al-anode, P=240 W, as reported previously 42 . We charge calibrated the documented spectra using the signal at 284.5 8 eV corresponding to the aliphatic carbon C-1s and the "CasaXPS", software version 2.3. ...
... A common feature of these applications is the need for the on-base growth of the porous nanomaterial from a processable substrate, such as transparent conducting oxides (TCOs), or on-device architecture, such as interdigitated electrodes (Romero-Gómez et al., 2010;Sánchez-Valencia et al., 2010;Cerofolini et al., 2011;Sun et al., 2012;Zhang et al., 2012;Dave and Malpani, 2014;Wu et al., 2014a,b;Barranco et al., 2016;Sk et al., 2016;Ferrando-Villalba et al., 2018;Ramirez-Gutierrez et al., 2019;Luo et al., 2020). In consequence, the number of publications devoted to the tunable deposition of metal and metal oxide porous systems including chemical solution methods, electrodeposition or electrospinning, and vacuum phase as physical vapor deposition and chemical vapor deposition has enormously increased (Hodes, 2007;Jerónimo et al., 2007;Romero-Gómez et al., 2010;Sánchez-Valencia et al., 2010;Cerofolini et al., 2011;Kim and Rothschild, 2011;Sun et al., 2012;Zhang et al., 2012;Pal and Bhaumik, 2013;Dave and Malpani, 2014;Lee and Park, 2014;Sun and Xu, 2014;Wu et al., 2014a,b;Malgras et al., 2015;Barranco et al., 2016;Sk et al., 2016;Xue et al., 2017;Ferrando-Villalba et al., 2018;Liu et al., 2018;Coll and Napari, 2019;Ramirez-Gutierrez et al., 2019;Luo et al., 2020;Siebert et al., 2020). In the case of vacuum phase approaches, the methodologies previously developed for the synthesis of highly compact films, such as thermal, electronbeam or ion-assisted evaporation, magnetron sputtering, atomic layer deposition (ALD), and plasma enhanced chemical vapor deposition (PECVD) have been thoroughly modified and expanded to produce microporous and mesoporous layers (Romero-Gómez et al., 2010;Sánchez-Valencia et al., 2010;Borras et al., 2012;Barranco et al., 2016;Coll and Napari, 2019;. ...
... The printed Cu and Fe microparticles were annealed at 425 °C in the air for 4 h, leading to highly porous bridging non-planar CuO/Cu2O/Cu-Fe2O3/Fe nanostructures beneficial for sensitive detection. The lowest power consumption was about 0.26 µW for 100 ppm acetone[91]. ...
Article
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With the global population prevalence of diabetes surpassing 463 million cases in 2019 and diabetes leading to millions of deaths each year, there is a critical need for feasible, rapid, and non-invasive methodologies for continuous blood glucose monitoring in contrast to the current procedures that are either invasive, complicated, or expensive. Breath analysis is a viable methodology for non-invasive diabetes management owing to its potential for multiple disease diagnoses, the nominal requirement of sample processing, and immense sample accessibility; however, the development of functional commercial sensors is challenging due to the low concentration of volatile organic compounds (VOCs) present in exhaled breath and the confounding factors influencing the exhaled breath profile. Given the complexity of the topic and the sky-rocketing spread of diabetes, a multifarious review of exhaled breath analysis for diabetes monitoring is essential to track the technological progress in the field and comprehend the obstacles in developing a breath analysis-based diabetes management system. In this review, we consolidate the relevance of exhaled breath analysis through a critical assessment of current technologies and recent advancements in sensing methods to address the shortcomings associated with blood glucose monitoring. We provide a detailed assessment of the intricacies involved in the development of non-invasive diabetes monitoring devices. In addition, we spotlight the need to consider breath biomarker clusters as opposed to standalone biomarkers for the clinical applicability of exhaled breath monitoring. We present potential VOC clusters suitable for diabetes management and highlight the recent buildout of breath sensing methodologies, focusing on novel sensing materials and transduction mechanisms. Finally, we portray a multifaceted comparison of exhaled breath analysis for diabetes monitoring and highlight remaining challenges on the path to realizing breath analysis as a non-invasive healthcare approach.
... Adelung et al. developed an acetone sensor based on a mixture of semiconductor metal oxides by DIW assembly. 134 The device was manufactured by directly writing metallic NPs (iron and copper NPs) onto the target substrate, followed by thermal annealing to form a bridged polyphase semiconductor oxide network. The gas sensor was selective to acetone vapor with a high gas response of approximately 50%, and the lowest operating power was approximately 0.26 mW to 100 ppm. ...
Article
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Functional nanoparticles (NPs) with unique photoelectric, mechanical, magnetic, and chemical properties have attracted considerable attention. Aggregated NPs rather than individual NPs are generally required for sensing, electronics, and catalysis. However, the transformation of functional NP aggregates into scalable, controllable, and affordable functional devices remains challenging. Printing is a promising additive manufacturing technology for fabricating devices from NP building blocks because of its capabilities for rapid prototyping and versatile multifunctional manufacturing. This paper reviews recent advances in NP patterning based on the combination of self-assembly and printing technologies (including two-, three-, and four-dimensional printing), introduces the basic characteristics of these methods, and discusses various fields of NP patterning applications.
... Different preparation methods provide distinct structural and physical properties of CuO suitable for various applications including solar cells [36], lithium ion batteries [37], electrochemical sensors [38], optical sensors [39] and gas sensors [40][41][42]. For instance, A.S. Zoolfakar et al. [43] fabricated a gas sensor based on CuO semiconductor nanostructured thin film via radio-frequency sputtering exhibiting a sensor response (R g /R a where R g and R a were the resistance of the sensor when exposed to gas and ambient air, respectively) of 2. [45] presenting decent gas responses of ~1.5 and 2.5-100 ppm acetone at 300 • C and 350 • C, respectively. Nevertheless, there is still no application of 3D-printed CuO structures produced by FDM to room-temperature ammonia gas-sensing applications. ...
Article
In this work, a new room-temperature ammonia gas sensor based on n-type copper oxide (CuO) semiconductor was fabricated by 3D printing with fused deposition modeling (FDM) technique and sintering method. The polylactic acid (PLA) was blended together with Cu particles and extruded into the filament form for FDM printing. The PLA/Cu composite was printed and calcined in a furnace to obtain semiconducting CuO. The structural characterization results of 3D printed sensor showed monoclinic CuO phase and scaffold structures, which provided active porous sites for enhanced gas adsorption and room-temperature gas-sensing performances. According to gas-sensing data, the 3D printed CuO gas sensor exhibited good repeatability, high stability (>3 months), low humidity dependency (25–65 %RH), high sensitivity and selectivity towards ammonia at room temperature. The sensor response increased linearly with increasing NH3 concentration from 25 to 200 ppm. The sensing mechanism of the 3D printed CuO sensor was proposed based on the resistance change via reaction on adsorbed surface oxygen species or direct electron transfer between ammonia molecules and CuO. This approach could open up new ways to fabricate semiconductor gas sensors with controllable sizes and shapes for future gas-sensing applications.
... Conventional MOS-based gas sensors usually operate at high temperatures ranging from 100 to 450 • C in order to achieve enhanced sensing performance because of their larger band gap [77,131], which leads to serious problems such as high-power consumption and increase of overall price of the gas sensor due to need for the heater. Thus, RT operation of gas sensors is highly desirable to minimize the risk of gas explosion, reduction of energy consumption, increases sensor life and possibility of integration into smart phone devices [132,133]. ...
Article
With the tremendous advances in technology, gas-sensing devices are being popularly used in many distinct areas, including indoor environments, industries, aviation, and detectors for various toxic domestic gases and vapors. Even though the most popular type of gas sensor, namely, resistive-based gas sensors, have many advantages over other types of gas sensors, their high working temperatures lead to high energy consumption, thereby limiting their practical applications, especially in mobile and portable devices. As possible ways to deal with the high-power consumption of resistance-based sensors, different strategies such as self-heating, MEMS technology, and room-temperature operation using especial morphologies, have been introduced in recent years. In this review, we discuss different types of energy-saving chemisresitive gas sensors and their application in the fields of environmental monitoring. At the end, the review will be concluded by providing a summary, challenges and future perspectives.
... Therefore, this hydrogel can be ink-written into various shapes for wearable optical devices, colorimetric tactile sensors, and full-color displays. Siebert et al. firstly directly wrote mixed metal microparticles arrays of commercially available Fe and Cu particles onto the glass substrate for sensing acetone gas (Siebert et al., 2020). After thermal annealing, the mixed metal microparticles formed open, highly porous nanostructures based on bridging CuO/Cu 2 O/Cu-Fe 2 O 3 /Fe heterojunction networks, achieving high selectivity and sensitivity to acetone vapor at an operating temperature of 300 • C and operating power as low as 0.26 µW. ...
Article
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Recently, the fabrication of electronics-related components via direct ink writing (DIW) has attracted much attention. Compared to the conventionally fabricated electronic components, DIW-printed ones have more complicated structures, higher accuracy, improved efficiency, and even enhanced performances that arise from well-designed architectures. The DIW technology allows directly print materials on a variety of flat substrates, even a conformal one, well suiting them to applications such as wearable devices and on-chip integrations. Here, recent developments in DIW printing of emerging components for electronics-related applications are briefly reviewed, including electrodes, electronic circuits, and functional components. The printing techniques, processes, ink materials, advantages, and properties of DIW-printed architectures are discussed. Finally, the challenges and outlooks on the manufacture of 3D structured electronic devices by DIW are outlined, pointing out future designs and developments of DIW technology for electronics-related applications. The combination of DIW and electronic devices will help to improve the quality of human life and promote the development of science and society.
... Finally, we integrate the micro-structured oxides with MEMS-electrodes to manufacture SnO 2 gas sensors. Compared to other previous reports of printed gas sensors, [35][36][37] the gas-sensitive layers are fabricated in a 3D structure for the first time. The gas sensing measurements show that the printed SnO 2 exhibits excellent sensing properties to acetylene and long-term stability. ...
Article
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Micrometer-resolution 3D printing of functional oxides is of growing importance for the fabrication of micro-electromechanical systems (MEMSs) with customized 3D geometries. Compared to conventional microfabrication methods, additive manufacturing presents new opportunities for the low-cost, energy-saving, high-precision, and rapid manufacturing of electronics with complex 3D architectures. Despite these promises, methods for printable oxide inks are often hampered by challenges in achieving the printing resolution required by today's MEMS electronics and integration capabilities with various other electronic components. Here, a novel, facile ink design strategy is presented to overcome these challenges. Specifically, we first prepare a high-solid loading (∼78 wt%) colloidal suspension that contains polyethyleneimine (PEI)-coated stannic dioxide (SnO2) nanoparticles, followed by PEI desorption that is induced by nitric acid (HNO3) titration to optimize the rheological properties of the printable inks. Our achieved ∼3-5 μm printing resolution is at least an order of magnitude higher than those of other printed oxide studies employing nanoparticle ink-based printing methods demonstrated previously. Finally, various SnO2 structures were directly printed on a MEMS-based microelectrode for acetylene detection application. The gas sensitivity measurements reveal that the device performance is strongly dependent on the printed SnO2 structures. Specifically, the 3D structured SnO2 gas sensor exhibits the highest response of ∼ 29.9 to 100 ppm acetylene with the fastest total response time of ∼ 65.8 s. This work presents a general ink formulation and printing strategy for functional oxides, which further provides a pathway for the additive manufacturing of oxide-based MEMSs.
... The combined diffusion spectra were recorded using a WITec alpha300 Raman spectrometer. All micro-Raman spectra were taken with the help of WITec RA300 microscope (the excitation light, 532 nm), to identify the phase of materials as described in previous papers [25,38]. ...
Article
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In this work, the β-Ga2O3 nanostructures were obtained by thermal annealing in air of β-Ga2S3 single crystals at relatively high temperatures of 970 K, 1070 K and 1170 K for 6 h. The structural, morphological, chemical and optical properties of β-Ga2O3–β-Ga2S3 layered composites grown at different temperatures were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) as well as photoluminescence spectroscopy (PL) and Raman spectroscopy. The results show that the properties of obtained β-Ga2O3–β-Ga2S3 composites were strongly influenced by the thermal annealing temperature. The XRD and Raman analyses confirmed the high crystalline quality of the formed β-Ga2O3 nanostructures. The absorption edge of the oxide is due to direct optical transitions. The optical bandwidth was estimated to be approximately 4.34-4.41 eV, depending on the annealing temperature. Annealing of the β-Ga2S3 monocrystals at a higher temperature of 1170 K showed the complete conversion of the surface to β-Ga2O3. These results demonstrate the possibility to grow high quality β-Ga2O3–β-Ga2S3 layered composites and β-Ga2O3 nanostructures in large quantities for various applications such as gas sensing, non-toxic biomedical imaging, nonlinear optical, as well as power device applications. Micro and nanocrystallites present on the surface of the Ga2O3 layer contribute to a diffusion of the incident light which leads to an increase of the absorption rate allowing thus to reduce the thickness of the Ga2O3 layer, in which the generation of unbalanced charge carriers takes place. By decreasing the Ga2O3 layer thickness, the efficiency of photovoltaic cells based on such junctions can be increased.
... A common feature of these applications is the need for the on-base growth of the porous nanomaterial from a processable substrate, such as transparent conducting oxides (TCOs), or on-device architecture, such as interdigitated electrodes (Romero-Gómez et al., 2010;Sánchez-Valencia et al., 2010;Cerofolini et al., 2011;Sun et al., 2012;Zhang et al., 2012;Dave and Malpani, 2014;Wu et al., 2014a,b;Barranco et al., 2016;Sk et al., 2016;Ferrando-Villalba et al., 2018;Ramirez-Gutierrez et al., 2019;Luo et al., 2020). In consequence, the number of publications devoted to the tunable deposition of metal and metal oxide porous systems including chemical solution methods, electrodeposition or electrospinning, and vacuum phase as physical vapor deposition and chemical vapor deposition has enormously increased (Hodes, 2007;Jerónimo et al., 2007;Romero-Gómez et al., 2010;Sánchez-Valencia et al., 2010;Cerofolini et al., 2011;Kim and Rothschild, 2011;Sun et al., 2012;Zhang et al., 2012;Pal and Bhaumik, 2013;Dave and Malpani, 2014;Lee and Park, 2014;Sun and Xu, 2014;Wu et al., 2014a,b;Malgras et al., 2015;Barranco et al., 2016;Sk et al., 2016;Xue et al., 2017;Ferrando-Villalba et al., 2018;Liu et al., 2018;Coll and Napari, 2019;Ramirez-Gutierrez et al., 2019;Luo et al., 2020;Siebert et al., 2020). In the case of vacuum phase approaches, the methodologies previously developed for the synthesis of highly compact films, such as thermal, electronbeam or ion-assisted evaporation, magnetron sputtering, atomic layer deposition (ALD), and plasma enhanced chemical vapor deposition (PECVD) have been thoroughly modified and expanded to produce microporous and mesoporous layers (Romero-Gómez et al., 2010;Sánchez-Valencia et al., 2010;Borras et al., 2012;Barranco et al., 2016;Coll and Napari, 2019;. ...
Article
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The large area scalable fabrication of supported porous metal and metal oxide nanomaterials is acknowledged as one of the greatest challenges for their eventual implementation in on-device applications. In this work, we will present a comprehensive revision and the latest results regarding the pioneering use of commercially available metal phthalocyanines and porphyrins as solid precursors for the plasma-assisted deposition of porous metal and metal oxide films and three-dimensional nanostructures (hierarchical nanowires and nanotubes). The most advanced features of this method relay on its ample general character from the point of view of the porous material composition and microstructure, mild deposition and processing temperature and energy constrictions and, finally, its straightforward compatibility with the direct deposition of the porous nanomaterials on processable substrates and device-architectures. Thus, taking advantage of the variety in the composition of commercially available metal porphyrins and phthalocyanines, we present the development of metal and metal oxides layers including Pt, CuO, Fe2O3, TiO2, and ZnO with morphologies ranging from nanoparticles to nanocolumnar films. In addition, we combine this method with the fabrication by low-pressure vapor transport of single-crystalline organic nanowires for the formation of hierarchical hybrid organic@metal/metal-oxide and @metal/metal-oxide nanotubes. We carry out a thorough characterization of the films and nanowires using SEM, TEM, FIB 3D, and electron tomography. The latest two techniques are revealed as critical for the elucidation of the inner porosity of the layers.
... For example, the developed sensors based on hybrid ZnO-Bi 2 O 3 and ZnO-ZTO exhibited good response to explosive and toxic gases, including of H 2 , CH 4 , and CO [19]. The mixed semiconducting metal oxides of Fe 2 O 3 -CuO nanostructurea exhibited the low response of about 50 % for 100 ppm acetone at 300 • C [20]. However, the pristine or mixed binary oxides possess low sensitivity, poor selectivity, and instability at low gas concentrations, so hindering their practical applications [19,21,22] Recently, ternary oxides [23] have been of great interest as gas sensitive materials because they have many advantages [24] over the binary oxides [25], including high catalytic activity, chemical inertness, thermal stability, environmental friendliness, and high gas sensitivity [26][27][28]. ...
Article
People in developing countries are facing various fatal diseases like cancer, pneumonia, tuberculosis and especially diabetes due to the lack of low cost and effective diagnosis methods. Design and fabrication of effective materials for VOC gas sensor applications towards exhaled breath analysis in diabetic diagnosis is challenging because the gas sensing performance of metal oxides is dependent on their composition, structure, and morphology. Here, Zn2SnO4 (ZTO) nanoparticles, hollow cubes, and hollow octahedra were successfully synthesized for VOCs gas sensing applications. The synthesized materials were characterized by advanced techniques while the gas sensing properties of the synthesized materials were tested for the detection of VOCs (acetone, ethanol, methanol), NH3, H2, and CO over the temperature range of 350 °C―450 °C. The ZTO hollow cubes and hollow octahedra exhibited exceptionally high sensitivity towards 125 ppm acetone at 450 °C with the response values of 47.80 and 63.93, respectively. The ZTO sensors also exhibited good selectivity and stability, with the theoretical calculation detection limits towards acetone being 175 ppb and 0.67 ppb for hollow cubes and hollow octahedra, respectively. The developed ZTO sensor maintained its performance after several tens of testing cycles, and few months storage in ambient air. The high gas-sensing performance of the ZTO hollow cubes and hollow octahedra to acetone was explained by an increase in the pore size, porosity, and oxygen vacancies. The above results suggest that the ZTO hollow octahedra and the hollow cubes are promising sensing materials for the detection of VOCs in diabetic diagnosis applications.
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In this study, a strategy to prepare CuO/Cu2O/Cu microwires which is fully covered by a nanowire network using a simple thermal oxidation process is developed. The CuO/Cu2O/Cu-microwires are fixed on Au/Cr pads with Cu microparticles. After thermal annealing at 425 °C, these CuO/Cu2O/Cu microwires are used as room-temperature 2-propanol sensors. These sensors show different dominating gas responses with operating temperatures, for example, higher sensitivity to ethanol at 175 oC, higher sensitivity to 2-propanol at room temperature and 225 oC, and higher sensitivity to hydrogen gas at ~ 300 oC, respectively. In this context, we propose the sensing mechanism of this 3-in-1 sensor based on CuO/Cu2O/Cu. XRD studies reveal that the annealing time during oxidation affects the chemical appearance of the sensor, while the intensity of reflections proves that for samples oxidized at 425 ºC for 1 h the dominating phase is Cu2O, whereas upon further rising the annealing duration up to 5 h, the CuO phase becomes dominant. The crystal structure of the Cu2O-shell/Cu-core and the CuO-NWs networks on the surface were confirmed with TEM, HRTEM, and SAED, where (HR)TEM micrographs reveal the monoclinic CuO phase. DFT calculations brings valuable inputs to the interactions of the different gas molecules with the most stable topsurface of CuO, revealing strong binding, electronic band gap changes and charge transfer dueto the gas molecule interactions with the topsurface. This research shows the importance of the non-planar CuO/Cu2O layered hetero-structure as a bright nanomaterial for the detection of various gases, controlled by the working temperature, and the insight presented here will be of significant value in the fabrication of new p-type sensing devices through simple nanotechnology.
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Information about the surrounding atmosphere at a real timescale significantly relies on available gas sensors to be efficiently combined into multisensor arrays as electronic olfaction units. However, the array's performance is challenged by the ability to provide orthogonal responses from the employed sensors at a reasonable cost. This issue becomes more demanded when the arrays are designed under an on-chip paradigm to meet a number of emerging calls either in the internet-of-things industry or in situ noninvasive diagnostics of human breath, to name a few, for small-sized low-powered detectors. The recent advances in additive manufacturing provide a solid top-down background to develop such chip-based gas-analytical systems under low-cost technology protocols. Here, we employ hydrolytically active heteroligand complexes of metals as ink components for microplotter patterning a multioxide combinatorial library of chemiresistive type at a single chip equipped with multiple electrodes. To primarily test the performance of such a multisensor array, various semiconducting oxides of the p- and n-conductance origins based on pristine and mixed nanocrystalline MnO x , TiO2, ZrO2, CeO2, ZnO, Cr2O3, Co3O4, and SnO2 thin films, of up to 70 nm thick, have been printed over hundred μm areas and their micronanostructure and fabrication conditions are thoroughly assessed. The developed multioxide library is shown to deliver at a range of operating temperatures, up to 400 °C, highly sensitive and highly selective vector signals to different, but chemically akin, alcohol vapors (methanol, ethanol, isopropanol, and n-butanol) as examples at low ppm concentrations when mixed with air. The suggested approach provides us a promising way to achieve cost-effective and well-performed electronic olfaction devices matured from the diverse chemiresistive responses of the printed nanocrystalline oxides.
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The detection of formaldehyde is closely-related to human’s daily life. Titanium oxide (TiO2) based nanomaterials are of great promise for formaldehyde detection due to their wide availability, easy utilization and abundant surface reactions. However, currently their actual application is still limited by the relatively low sensitivity, high working temperature and poor selectivity. To address these issues, herein we develop a template-assisted self-assembly strategy to realize the simultaneous chemical doping and morphological control of TiO2 nanostructures. The resultant Co-doped TiO2 nanospheres show a high-level cobalt content up to 2.95 wt.% and a unique raspberry-like mesoporous morphology composed of numerous superfine nanopores of 4.9-7.8 nm, which renders a large specific surface area (~175 m2/g) and high porosity (0.438 cm3/g) of the product. The corresponding gas sensor device shows a sensitivity of ~84.8 for 10 ppm formaldehyde, which exceeds most of the similar metal oxides reported recently and likely stands for the state-of-the-art merit of the formaldehyde-sensors. Meanwhile, the sensor also shows significantly decreased working temperature (~86 °C) and unique selectivity. These all make our chemically-doped raspberry-like mesoporous TiO2 product a very promising candidate for future formaldehyde sensors.
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The fabrication of chemiresistive sensors by inkjet printing is recognized as a breakthrough in gas-sensing applications. One challenge of this technology, however, is how to enhance the cross-selectivity of the sensor array. Herein, we present a ketjen black (KB) ink and molecularly imprinted sol-gel (MISG) inks to support the fabrication of a fully inkjet-printed chemiresistive sensor array, enabling the highly accurate recognition of volatile organic acids (VOAs) on the molecular level. The MISG/KB sensor array was prepared on a glossy photographic paper with a three-layer structure: a circuit layer by a commercial silver ink, a conductive layer by a KB ink, and an active selective layer by MISG inks imprinted by different templates. Hexanoic acid (HA), heptanoic acid, and octanoic acid were used as templates to prepare the MISGs and as targets to evaluate the detection and discrimination performance of the sensor array. Three resultant MISG/KB sensors exhibited high sensitivity and selectivity to VOA vapors. The limit of detection and imprinting factor were 0.018 ppm and 7.82, respectively, for HA-MISG/KB sensors to the corresponding target. With linear discriminant analysis of the gas responses, the MISG/KB sensor array can realize high discrimination to VOAs in single and binary mixtures. Furthermore, the proposed sensor array showed strong sensor robustness with excellent consistency, durability, bending, and humidity resistance. This work developed a fully inkjet-printed chemiresistive sensor array, enabling the realization of high cross-selectivity detection, achieving low-cost, scalable, and highly reproducible sensor fabrication, moving it closer to reliable, commercial, and wearable multi-analyte human body odor analysis potential.
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Semiconducting metal oxide - based gas sensors exhibit outstanding sensitivity, although humidity in the analyte typically hampers precise measurements. In this work it was shown that a 5-6 nm thin Al2O3 nano-layer is particularly beneficial in reducing the interference due to humidity of p-type conductivity copper oxide-based gas sensors. An effective approach from chemical solutions at 75 °C and thermal annealing at 600 °C was used to grow copper oxide nano-crystallite layers. The Al2O3 nano-layers were subsequently deposited on top of copper oxide by atomic layer deposition in a high-aspect-ratio regime at 75 °C. The morphological, structural, chemical, vibrational, electronical and sensor characteristics of the heterostructured nano-crystallite layers have been studied. The final nano-Al2O3/CuO heterostructure showed an increase in the response to H2 gas by 140 %, while long-term stability at low and high relative humidity was observed. The initial sensing response varied by only 10% for an Al2O3 layer of 5-6 nm on top of CuO with a post-thermal annealing at 600 °C acting as an effective barrier for water vapor and oxygen. A comparison with CuO nanocrystallite layers covered by ALD with 6 nm and 15 nm of Al2O3 ultra-thin films on top demonstrates an exceptional stability of the hydrogen gas response at high relative humidity (84% RH). Density functional theory-based calculations showed that the H2 molecule spontaneously dissociates over the formed Al2O3/CuO heterostructure, interacting strongly with the surface Al atoms, showing different behavior compared to the pristine CuO (111) surface, where H2 gas molecules are known to form water over the surface. The present study demonstrates that a thorough optimization of technology and surface properties due to coverage and formation of heterostructured nano-materials improves the humidity stability during H2 gas sensing applications which is important for real-world applications, e.g. portable battery analysis, H2 breath tests, along with environmental, medicine, security, and food safety diagnostic tests.
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MXene combining with metal oxide semiconductor (MOS) can improve carrier transfer rate, inhibit agglomeration, and promote the improvement of gas-sensing performance. In this article, the heterogeneous composites of α-Fe2O3 and Ti3C2Tx MXene were successfully synthesized through a facile hydrothermal route, and characterized the morphology and microstructure by various characterizations. The results revealed that the α-Fe2O3 nanocubes with sizes of around 250 nm in width were prepared and uniformly distributed to the surface of the Ti3C2Tx MXene nanosheet. Gas-sensing test results illustrated that the α-Fe2O3/Ti3C2Tx MXene composites-based sensor exhibited outstanding selectivity to acetone compared with other typical gases, and illustrated a high response (16.6% to 5 ppm acetone), the fast response and recovery speeds (5/5 s), superb linearity and prominent repeatability at room temperature (RT). Furthermore, the gas-sensing mechanism of the α-Fe2O3/Ti3C2Tx MXene sensor toward acetone is discussed by density functional theory (DFT) calculation. This work is expected to provide useful reference to develop other promising hybrids for acetone sensing at RT.
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Zinc oxide is widely used in gas sensors, solar cells, and photocatalysts because of its wide bandgap and exciton binding energy of 60 meV in various metal oxides. To use ZnO as a gas sensor, it is necessary to synthesize it with surface defects and a large specific surface area. In this study, hydrothermal synthesis without surfactants was employed to obtain organic-additive-free ZnO. For morphology control, we varied the ratio of the hydroxide ion concentration to the zinc ion concentration. To confirm the growth mechanism of ZnO, we performed X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses. Raman spectroscopy and photoluminescence measurements were performed to analyze the surface properties. The Brunauer–Emmett–Teller method and probe stations were used to measure the specific surface area and sensitivity of the gas sensor, respectively. The results confirmed that flower-shaped ZnO is the most suitable gas-sensing material.
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Acetone commonly exists in daily life and is harmful to human health, therefore the convenient and sensitive monitoring of acetone is highly desired. In addition, flexible sensors have the advantages of light-weight, conformal attachable to irregular shapes, etc. In this study, we fabricated high performance flexible silicon nanowires (SiNWs) sensor for acetone detection by transferring the monocrystalline Si film and metal-assisted chemical etching method on polyethylene terephthalate (PET). The SiNWs sensor enabled detection of gaseous acetone with a concentration as low as 0.1 parts per million (ppm) at flat and bending states. The flexible SiNWs sensor was compatible with the CMOS process and exhibited good sensitivity, selectivity and repeatability for acetone detection at room temperature. The flexible sensor showed performance improvement under mechanical bending condition and the underlying mechanism was discussed. The results demonstrated the good potential of the flexible SiNWs sensor for the applications of wearable devices in environmental safety, food quality, and healthcare.
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In a wide range of applications, rapid fabrication of metallic patterns on a transparent substrate is highly desired. In this work, a highly conductive Cu wire with a sheet resistance of 0.27 Ω/sq is deposited on glass through femtosecond laser-induced reduction of Cu ions. The present work improves the deposition efficiency by at least one order of magnitude compared to previous works. The effects of scanning speed, laser intensity, and effective pulse number on composition, morphology, dimensions, and conductivity of the deposited Cu are investigated. The process window is established with the goal of achieving optimal laser parameters for creating highly conductive Cu. With a scanning speed of 600 mm/s, an intensity of 1.21 × 10¹⁰ W/cm², and an effective pulse number of 38500, the well-formed Cu in the process window has a sheet resistance of less than 1 Ω/sq and the highest deposited efficiency of 4.60 × 10⁷ μm³/s. The current-carrying performance of the deposited Cu is also investigated for prospective use as a circuit material, demonstrating the Cu wire’s electrical and thermal durability. In addition, temperature rise could be estimated from Cu wire width and sheet resistance with given Cu wire length and applied current, which could aid in laser parameter selection.
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Lately novel strategies to enhance the sensing properties on iron oxide have been proposed to achieve high performance gas sensors for acetone detection. In this working report, the synthesis of iron-glycerate (Fe-Gly) using glycerol to combine with Fe ³⁺ is first presented. Depending on the thermal treatment, this compound can evolve into γ-Fe 2 O 3 , α/γ-Fe 2 O 3 and α-Fe 2 O 3 . α/γ-Fe 2 O 3 shows better sensing performance as far as acetone detection is concerned. Using the dual phases of α/γ-Fe 2 O 3 as a fundamental building block, their sensing properties were further improved using Ni doping and Ru nanoparticles functionalization. The high response and selectivity to acetone detection was ascribed to the synergistic effects of unique nanosheets, mixed phases, rich oxygen vacancies and excellent catalytic activity of Ru nanoparticles. Graphical abstract
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Acetone, with diverse applications in multiple areas, may pose a risk to industrial safety and human health. For the purpose of detecting the leakage and concentration of acetone, we have successfully prepared [MIL-125(Ti)/FexTiyOz]T-X (MFTT-X) gas-sensitive materials by in-situ solvothermal and calcination methods. Herein, the porous MIL-125(Ti) and FexTiyOz nanoparticles with intimate interfaces are grown on the template of exfoliated Ti3C2Tx nanosheets that simultaneously serve as the Ti source. The narrower bandgap, numerous surface defects, increased specific surface area, and mesoporous structure of MFTT-X composites are conducive to the diffusion and contact among acetone gas and active sites. The optimum MFT450-8 composite endows significantly enhanced sensitivity (R = 351.1) towards 100 ppm acetone at 222 °C, ultrafast response and recovery time (16 s / 5 s), good repeatability, and excellent selectivity. These results provide new insight into the design of high-performance sensing materials, modified with MXene derived MOFs, and analyzed the reaction mechanism of acetone that is relevant to MFT450-8 composite.
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In this work, a room temperature (RT) operated acetone (C3H6O) sensor having good sensing characteristics like good % response, fast response and recovery times, good selectivity, and substantial stability is developed using SnO2-polythiophene (PTh) nanocomposite. The electrospinning technique is used for depositing SnO2 nanofibers(diameter 80-160 nm) followed by polymerization of thiophene to develop SnO2/PTh nanocomposite. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR) results are used to examine the structural, morphological, and elemental analysis of the SnO2/PTh nanocomposite. The mean crystallite size of the nanocomposite is observed to be 10.6 nm. The acetone sensing performance of the developed sensor is analyzed in concentration range of 0.5-20 ppm at RT (27 °C) under 45% relative humidity (RH) conditions. The sensor showed highly stable response with good sensing characteristics toward acetone detection having 12.7% response for 0.5 ppm with fast response (10 s) and recovery (14 s) times. The response of the sensor reached up to 131.1% for 20 ppm of acetone. Synergistic effect and p-n heterojunction formation at interface in SnO2/PTh nanocomposite are believed to be the major factors for achieving good sensing performance at RT.
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Production of objects with varied mechanical properties is challenging for current manufacturing methods. Additive manufacturing could make these multimaterial objects possible, but methods able to achieve multimaterial control along all three axes of printing are limited. Here we report a multi-wavelength method of vat photopolymerization that provides chemoselective wavelength-control over material composition utilizing multimaterial actinic spatial control (MASC) during additive manufacturing. The multicomponent photoresins include acrylate- and epoxide-based monomers with corresponding radical and cationic initiators. Under long wavelength (visible) irradiation, preferential curing of acrylate components is observed. Under short wavelength (UV) irradiation, a combination of acrylate and epoxide components are incorporated. This enables production of multimaterial parts containing stiff epoxide networks contrasted against soft hydrogels and organogels. Variation in MASC formulation drastically changes the mechanical properties of printed samples. Samples printed using different MASC formulations have spatially-controlled chemical heterogeneity, mechanical anisotropy, and spatially-controlled swelling that facilitates 4D printing.
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The review describes the technologies used in the field of breath analysis to diagnose and monitor diabetes mellitus. Currently the diagnosis and monitoring of blood glucose and ketone bodies that are used in clinical studies involve the use of blood tests. This method entails pricking fingers for a drop of blood and placing a drop on a sensitive area of a strip which is pre-inserted into an electronic reading instrument. Furthermore, it is painful, invasive and expensive, and can be unsafe if proper handling is not undertaken. Human breath analysis offers a non-invasive and rapid method for detecting various volatile organic compounds thatare indicators for different diseases. In patients with diabetes mellitus, the body produces excess amounts of ketones such as acetoacetate, beta-hydroxybutyrate and acetone. Acetone is exhaled during respiration. The production of acetone is a result of the body metabolising fats instead of glucose to produce energy. There are various techniques that are used to analyse exhaled breath including Gas Chromatography Mass Spectrometry (GC–MS), Proton Transfer Reaction Mass Spectrometry (PTR–MS), Selected Ion Flow Tube-Mass Spectrometry (SIFT–MS), laser photoacoustic spectrometry and so on. All these techniques are not portable, therefore this review places emphasis on how nanotechnology, through semiconductor sensing nanomaterials, has the potential to help individuals living with diabetes mellitus monitor their disease with cheap and portable devices.
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Future sensing applications will include high-performance features, such as toxin detection, real-time monitoring of physiological events, advanced diagnostics, and connected feedback. However, such multi-functional sensors require advancements in sensitivity, specificity, and throughput with the simultaneous delivery of multiple detection in a short time. Recent advances in 3D printing and electronics have brought us closer to sensors with multiplex advantages, and additive manufacturing approaches offer a new scope for sensor fabrication. To this end, we review the recent advances in 3D-printed cutting-edge sensors. These achievements demonstrate the successful application of 3D-printing technology in sensor fabrication, and the selected studies deeply explore the potential for creating sensors with higher performance. Further development of multi-process 3D printing is expected to expand future sensor utility and availability.
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In this work, a novel composed morphology of iron oxide micro-structures covered with very thin nanowires (NW) with diameter of 15 – 50 nm have been presented in premiere. By oxidizing metallic Fe micro-particles at 255 °C for 12 h and 24 h, dense iron oxide NW networks bridging pre-patterned Au/Cr pads were obtained. XPS studies reveal formation of α-Fe2O3 and Fe3O4 on the surface and it was confirmed by detailed HRTEM and SAED investigations that NWs are single phase α-Fe2O3 and some domains of single phase Fe3O4. Localized synthesis of such nano- and micro-particles directly on sensor platform/structure at 255 °C for 24 h and re-oxidation at 650 °C for 0.2-2 h, yield in highly performance and reliable detection of acetone vapour with fast response and recovery times. High repeatability and complete recovery of electrical resistance to initial baseline after exposure to analyte gas, demonstrates excellent potential for fabrication of reliable and robust nano- and micro-sensor structures for biomedical and cosmetic applications, since acetone being extremely inflammable it is important to rapidly detect leaks of acetone vapour to prevent explosions or flash fire. The p-type behavior of n-type α-Fe2O3 and half-metal Fe3O4 could be a consequence of interesting/new electrical and conduction properties of mixed phases of iron oxides. First nanosensors on single α-Fe2O3 nanowire were fabricated and studied showing excellent performances. Several nanodevices based on a single α-Fe2O3 NW with different diameters showing an increase in acetone response by decrease of diameter were developed. Our facile technological approach enables this nanomaterial as candidate for a range of applications in the field of nanoelectronics such as nanosensors and biomedicine devices, especially for breath analysis in the treatment of diabetes patients.
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In this work, the exceptionally improved sensing capability of highly porous three-dimensional (3-D) hybrid ceramic networks toward reducing gases is demonstrated for the first time. The 3-D hybrid ceramic networks are based on doped metal oxides (MexOy and ZnxMe1-xOy, Me= Fe, Cu, Al) and alloyed zinc oxide tetrapods (ZnO-T) forming numerous junctions and heterojunctions. A change in morphology of the samples and formation of different complex microstructures is achieved by mixing the metallic (Fe, Cu, Al) microparticles with ZnO-T grown by the flame transport synthesis (FTS) in different weight ratios (ZnO-T:Me, e.g., 20:1) followed by subsequent thermal annealing in air. The gas sensing studies reveal the possibility to control and change/tune the selectivity of the materials, depending on the elemental content ratio and the type of added metal oxide in the 3-D ZnO-T hybrid networks. While pristine ZnO-T networks showed a good response to H2 gas, a change/tune in selectivity to ethanol vapour with a decrease in optimal operating temperature was observed in the networks hybridized with Fe-oxide and Cu-oxide. In the case of hybridization with ZnAl2O4 an improvement of H2 gas response (to ≈ 7.5) was reached at lower doping concentrations (20:1), whereas the increase in concentration of ZnAl2O4 (ZnO-T:Al, 10:1), the selectivity changes to methane CH4 gas (response is about 28). Selectivity tuning to different gases is attributed to the catalytic properties of the metal oxides after hybridization, while the gas sensitivity improvement is mainly associated with additional modulation of the electrical resistance by the built-in potential barriers between n-n and n-p heterojunctions, during adsorption and desorption of gaseous species. Density functional theory based calculations provided the mechanistic insights into the interactions between different hybrid networks and gas molecules to support the experimentally observed results. The studied networked materials and sensor structures performances would provide particular advantages in the field of fundamental research, applied physics studies, industrial and ecological applications.
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To forecast future trends in diabetes prevalence, morbidity, and costs in the United States, the Institute for Alternative Futures has updated its diabetes forecasting model and extended its projections to 2030 for the nation, all states, and several metropolitan areas. This paper describes the methodology and data sources for these diabetes forecasts and discusses key implications. In short, diabetes will remain a major health crisis in America, in spite of medical advances and prevention efforts. The prevalence of diabetes (type 2 diabetes and type 1 diabetes) will increase by 54% to more than 54.9 million Americans between 2015 and 2030; annual deaths attributed to diabetes will climb by 38% to 385,800; and total annual medical and societal costs related to diabetes will increase 53% to more than $622 billion by 2030. Improvements in management reducing the annual incidence of morbidities and premature deaths related to diabetes over this time period will result in diabetes patients living longer, but requiring many years of comprehensive management of multiple chronic diseases, resulting in dramatically increased costs. Aggressive population health measures, including increased availability of diabetes prevention programs, could help millions of adults prevent or delay the progression to type 2 diabetes, thereby helping turn around these dire projections. (Population Health Management 20xx;xx:xxx-xxx).
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Fe 2 O 3 -decorated CuO nanorods were prepared by Cu thermal oxidation followed by Fe 2 O 3 decoration via a solvothermal route. The acetone gas sensing properties of multiple-networked pristine and Fe 2 O 3 -decorated CuO nanorod sensors were examined. The optimal operating temperature of the sensors was found to be 240°C. The pristine and Fe 2 O 3 -decorated CuO nanorod sensors showed responses of 586 and 1,090%, respectively, to 1,000 ppm of acetone at 240°C. The Fe 2 O 3 -decorated CuO nanorod sensor also showed faster response and recovery than the latter sensor. The acetone gas sensing mechanism of the Fe 2 O 3 -decorated CuO nanorod sensor is discussed in detail. The origin of the enhanced sensing performance of the multiple-networked Fe 2 O 3 -decorated CuO nanorod sensor to acetone gas was explained by modulation of the potential barrier at the Fe 2 O 3 -CuO interface, highly catalytic activity of Fe 2 O 3 for acetone oxidation, and the creation of active adsorption sites by Fe 2 O 3 nanoparticles.
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Objective: Endogenous acetone production is a by-product of the fat metabolism process. Because of its small size, acetone appears in exhaled breath. Historically, endogenous acetone has been measured in exhaled breath to monitor ketosis in healthy and diabetic subjects. Recently, breath acetone concentration (BrAce) has been shown to correlate with the rate of fat loss in healthy individuals. In this review, the measurement of breath acetone in healthy subjects is evaluated for its utility in predicting fat loss and its sensitivity to changes in physiologic parameters. Results: BrAce can range from 1 ppm in healthy non-dieting subjects to 1,250 ppm in diabetic ketoacidosis. A strong correlation exists between increased BrAce and the rate of fat loss. Multiple metabolic and respiratory factors affect the measurement of BrAce. BrAce is most affected by changes in the following factors (in descending order): dietary macronutrient composition, caloric restriction, exercise, pulmonary factors, and other assorted factors that increase fat metabolism or inhibit acetone metabolism. Pulmonary factors affecting acetone exchange in the lung should be controlled to optimize the breath sample for measurement. Conclusions: When biologic factors are controlled, BrAce measurement provides a non-invasive tool for monitoring the rate of fat loss in healthy subjects.
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In the 20 years since precession electron diffraction (PED) was introduced, it has grown from a little-known niche technique to one that is seen as a cornerstone of electron crystallography. It is now used primarily in two ways. The first is to determine crystal structures, to identify lattice parameters and symmetry, and ultimately to solve the atomic structure ab initio . The second is, through connection with the microscope scanning system, to map the local orientation of the specimen to investigate crystal texture, rotation and strain at the nanometre scale. This topical review brings the reader up to date, highlighting recent successes using PED and providing some pointers to the future in terms of method development and how the technique can meet some of the needs of the X-ray crystallography community. Complementary electron techniques are also discussed, together with how a synergy of methods may provide the best approach to electron-based structure analysis.
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Acetone is qualitatively known as a biomarker of diabetes; however, the quantitative information on acetone concentration in diabetic breath is incomplete, and the knowledge of correlations of breath acetone with diabetic diagnostic parameters, namely, blood glucose (BG) and glycohemoglobin A1C (A1C), are unknown. We utilized a pilot-scale breath acetone analyzer based on the cavity ringdown spectroscopy (CRDS) technique to conduct breath tests with 34 Type 1 diabetic (T1D), ten Type 2 diabetic (T2D) patients, and 15 apparently healthy individuals. Relations between breath acetone and BG, A1C, and several other bio indices, such as the type of diabetes, onset-time, gender, age, and weight were investigated. Our observations show that a linear correlation between the mean group acetone and the mean group BG level does exist (R = 0.98, P < 0.02) when all the T1D subjects tested are grouped by different BG levels, 40-100, 101-150, 151-200, and 201-419 mg/dL. Similarly, among the T1D subjects studied, when their A1C's are grouped by < 7, 7-9.9, and 10-13, a linear correlation between the mean group A1C and the mean group acetone concentration is observed (R = 0.98, P < 0.02). No strong correlations are observed when the BG and A1C numbers are not grouped. The mean breath acetone concentration in the T1D subjects studied in this work is determined to be 2.19 ppmv (parts per million by volume), which is higher than the mean breath acetone concentration, 0.48 ppmv, in the 15 healthy people tested.
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Conventional wisdom is that breath acetone may be markedly elevated in type 1 diabetes, but that this only occurs during poor blood glucose control and/or intercurrent illness. In contrast, little is known about breath acetone at more representative everyday blood glucose levels in diabetes. We used selected ion flow tube mass spectrometry to monitor the breath of eight patients with type 1 diabetes mellitus during 'insulin clamp' studies in which insulin and glucose were infused into patients to lower blood glucose levels in steps from normal values into the low glucose (hypoglycaemic) range. The concentration of acetone in breath and the blood sugar concentration of the patients were monitored at each blood glucose concentration. The blood glucose level at the start of the study was typically about 6 mM L(-1), whereas the breath acetone concentration at this blood glucose level was unexpectedly variable, ranging from 1 part-per-million to 21 ppm, in contrast to what was previously believed, i.e. that type 1 diabetes mellitus is characterized by high acetone levels. In all eight patients, the breath acetone declined linearly with blood glucose concentration.
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In this work, the one-step 3D-printing of 20 nm nanowire covered CuO/Cu2O/Cu microparticles (MPs) with diameters of 15-25 µm on the surface of glass substrate forming an ordered net is successfully reported for the first time. 3D-printed Cu MPs-based stripes formed non-planar CuO/Cu2O/Cu heterojunctions after thermal annealing at 425 C for 2 h in air and were fully covered with 20 nm nanowire net bridging MPs with external Au-contacts. The morphological, vibrational, chemical and structural investigations were performed in detail, showing the high crystallinity of the NWs and 3D-printed CuO/Cu2O/Cu heterojunctions lines, as well as the growth of CuO NWs on the surface of microparticles. The gas sensing measurements showed excellent selectivity to acetone vapor at an operating temperature of 350 C with a high gas response about 150% to 100 ppm. The combination of the possibility of fast acetone vapor detection, low power consumption and controllable size and geometry, make these 3D-printed devices ideal candidates for fast detection, as well as acetone vapor monitoring (down to 100 ppm). This 3D-printing approach will pave a new way for many different devices through the simplicity and versatility of the fabrication method for the exact detection of acetone vapors in various atmospheres.
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In this paper, the effect of the thickness of nano-structured TiO 2 thin films (12–40 nm) and successive deposition of different noble metal nanoparticles on the performances of propanol vapor and H 2 gas sensors was investigated. The obtained titania thin films were integrated into a device for UV, gas, and gas/vapor sensing studies at different operating temperatures. Qualitative analysis revealed that the sensor selectivity and its response could be altered by film thickness and type of noble metal nanoparticles. The results indicate that the sensor with 40 nm TiO 2 film has the highest response to H 2 gas (˜ 650%). The fastest response time and the most rapid recovery however were achieved by the sensors made of 12 nm sprayed TiO 2 ultra-thin films, which also offered the highest selectivity to H 2 gas. The best UV detection performances were demonstrated by films functionalized with Au nanoparticles (the I UV /I dark ≈ 80). The structural, chemical, electrical, UV, and gas sensing properties of such films were investigated using SEM, AFM, Raman spectroscopy, electrical characterization, and sensing experiments. It has been clearly demonstrated that films are nanostructured and have mixed phases that contain mostly anatase (annealed at 450 °C) and small amounts of rutile after thermal annealing at higher temperatures (more than 600 °C), as improved materials for sensor applications. Our combined study analyzes the relationship between thickness, electrical properties and the gas/vapor sensing performance of such thin film based TiO 2 gas sensors as well as the effect of different types of noble metal nanoparticles (Au, Ag, Ag-Au and Ag-Pt) deposited on the surface. The enhanced response was attributed to the involvement of noble nanoalloy or nanoparticle interface to titania forming nano-junctions in the gas sensing mechanism. Highly selective and sensitive sensors towards specific gas or vapor molecules are essential for environmental monitoring, and for health and safety issues.
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Morphology is a critical parameter for various thin film applications, influencing properties like wetting, catalytic performance and sensing efficiency. In this work, we report on the impact of oxygen partial flow on the morphology of ceramic thin films deposited by pulsed DC reactive magnetron sputtering. The influence of O2/Ar ratio was studied on three different model systems, namely Al2O3, CuO and TiO2. The availability of oxygen during reactive sputtering is a key parameter for a versatile tailoring of thin film morphology over a broad range of nanostructures. TiO2 thin films with high photocatalytic performance (up to 95% conversion in 7 h) were prepared, exhibiting a network of nanoscopic cracks between columnar anatase structures. In contrast, amorphous thin films without such crack networks and with high resiliency to crystallization even up to 950 °C were obtained for Al2O3. Finally, we report on CuO thin films with well aligned crystalline nanocolumns and outstanding gas sensing performance for volatile organic compounds as well as hydrogen gas, showing gas responses up to 35% and fast response in the range of a few seconds.
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For one-dimensional nanomaterials, the performances are strongly related to the diameters, lengths, morphologies, and structures, implying that it is of great significance to understand the related growth mechanisms and thus to achieve the desired nanostructures. Thermal oxidation of copper has been widely used to fabricate CuO nanowires (NWs), whereas the growth mechanism still remains controversial in spite of the extensive investigations. Therefore, this review aims to offer a critical discussion about the growth mechanisms. First, the effects of different growth conditions on the growth of CuO NWs are introduced for basic understanding. Subsequently, the proposed mechanisms in different literature studies, i.e., the vapor–solid, self-catalyzed growth, stress-induced growth, stress grain boundary (GB) diffusion, and oxygen concentration gradient, are discussed and summarized. It seems that the combination of “stress GB diffusion” and “oxygen concentration gradient” mechanisms could be relevant for the growth of CuO NWs via thermal oxidation of copper.
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Two modulated structures caused by long-range ordering of oxygen vacancies have been observed in α-Fe2O3 nanowires (NWs) produced after oxidation of Fe, one being ten times (303¯0) interplanar spacing and the other being six times (112¯0) interplanar spacing. Both types of oxygen vacancy ordering structures have a similar modulation periodicity of 1.45 or 1.50 nm with corresponding atomic ratios of Fe and O (Fe/O) of 0.7407 and 0.7273, respectively. The Fe/O ratios in the NWs with oxygen-vacancy ordering are very close to that of Fe3O4 (0.7500). The similar Fe/O ratio between NWs and Fe3O4 may explain the similar modulation periodicity of different oxygen-vacancy orderings. Electron energy-loss spectroscopy studies show that the Fe/O ratio of NWs is close to that of Fe3O4 when oxygen atoms are not sufficient, which makes the NWs energetically favorable. The elucidation of the mechanism governing the formation of the modulated structures in α-Fe2O3 NWs is critical for controlling the microstructure and correspondingly physicochemical properties of NWs.
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Three-dimensional printing (3DP) has attracted a considerable amount of attention during the past years, being globally recognized as one of the most promising and revolutionary manufacturing technologies. Although the field is rapidly evolving with significant technological advancements, materials research remains a spotlight of interest, essential for the future developments of 3DP. Smart polymers and nanocomposites, which respond to external stimuli by changing their properties and structure, represent an important group of materials that hold a great promise for the fabrication of sensors, actuators, robots, electronics, and medical devices. The interest in exploring functional materials and their 3DP are constantly growing in an attempt to meet the ever-increasing manufacturing demand of complex functional platforms in an efficient manner. In this review, we aim to outline the recent advances in the science and engineering of functional polymers and nanocomposites for 3DP technologies. The report covers temperature-responsive polymers, polymers and nanocomposites with electromagnetic, piezoresistive and piezoelectric behaviors, self-healing polymers, light- and pH- responsive materials, and mechanochromic polymers. The main objective is to link the performance and functionalities to the fundamental properties, chemistry, and physics of the materials, and to the process-driven characteristics, in an attempt to provide a multi-disciplinary image and a deeper understanding of the topic. The challenges and opportunities for future research are also discussed.
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Realization of high temperature physical measurement sensors, which are needed in many of the current and emerging technologies, is challenging due to the degradation of their electrical stability by drift currents, material oxidation, thermal strain, and creep. In this paper, for the first time, we demonstrate that 3D printed sensors show a metamaterial-like behavior, resulting in superior performance such as high sensitivity, low thermal strain, and enhanced thermal stability. The sensors were fabricated using silver (Ag) nanoparticles (NPs), using an advanced Aerosol Jet based additive printing method followed by thermal sintering. The sensors were tested under cyclic strain up to a temperature of 500 °C and showed a gauge factor of 3.15 ± 0.086, which is about 57% higher than that of those available commercially. The sensor thermal strain was also an order of magnitude lower than that of commercial gages for operation up to a temperature of 500 °C. An analytical model was developed to account for the enhanced performance of such printed sensors based on enhanced lateral contraction of the NP films due to the porosity, a behavior akin to cellular metamaterials. The results demonstrate the potential of 3D printing technology as a pathway to realize highly stable and high-performance sensors for high temperature applications.
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Detection and differentiation of volatile organic compounds (VOC) is highly important since these gaseous pollutants degrade air quality and represent, even in small amounts, a threat to human health. In this work, a simple and cost-efficient method to synthesize a multilayered (CuO-Cu2O)/ZnO:Al nanostructured film forming non-planar heterojunctions for efficient detection of volatile organic compound vapors is presented. While the ZnO:Al layer with different contents of Al (~ 0.1 and 0.2 at%) was deposited on a glass substrate via a synthesis from chemical solutions (SCS, at a temperature < 95 ºC), the CuO-Cu2O composite layer was formed by sputtering a metallic thin layer of Cu on top of the ZnO:Al nanocrystalline film and subsequent thermal annealing at 425 ºC. The highest gas response of ~ 200% to 100 ppm to n-butanol at 350 ºC operating temperature was observed in the case of a layer thickness of CuO-Cu2O ~ 20 nm on top of the ZnO:Al SCS samples. In this case, the enhanced response was attributed to the involvement of (CuO-Cu2O)/ZnO:Al interface junctions in the gas sensing mechanism. This top layer allows for the formation of an additional enclosed depletion layer, which leads to a higher modulation of the CuO-Cu2O resistance and thus to a higher gas response. The (CuO-Cu2O)/ZnO:Al heterojunction also showed a reduced dependence of the sensing properties with respect to relative humidity, which is very important for ambient gas sensing applications and VOCs vapor detection in human breath analysis, chemical industry, in outdoor and indoor air quality monitoring.
Chapter
It has been reported that concentrations of several biomarkers in diabetics’ breath show significant difference from those in healthy people’s breath. Concentrations of some biomarkers are also correlated with the blood glucose levels (BGLs) of diabetics. Therefore, it is possible to screen for diabetes and predict BGLs by analyzing one’s breath. In this chapter, we describe the design of a novel optimized breath analysis system for this purpose. The system uses carefully selected chemical sensors to detect biomarkers in breath. Common interferential factors, including humidity and the ratio of alveolar air in breath, are compensated or handled in the algorithm. Considering the inter-subject variance of the components in breath, we design a feature augmentation strategy to learn subject-specific prediction models to improve the accuracy of BGL prediction. 295 breath samples from healthy subjects and 279 samples from diabetic subjects were collected to evaluate the performance of the system. The sensitivity and specificity of diabetes screening are 91.51% and 90.77%, respectively. The mean relative absolute error for BGL prediction is 20.6%. Experiments show that the system is effective and that the strategies adopted in the system can improve its accuracy. The system potentially provides a noninvasive and convenient method for diabetes screening and BGL monitoring as an adjunct to the standard criteria.
Article
Layer-by-layer deposition of materials to manufacture parts - better known as three-dimensional (3D) printing or additive manufacturing - has been flourishing as a fabrication process in the past several years and now can create complex geometries for use as models, assembly fixtures, and production molds. Increasing interest has focused on the use of this technology for direct manufacturing of production parts; however, it remains generally limited to single-material fabrication, which can limit the end-use functionality of the fabricated structures. The next generation of 3D printing will entail not only the integration of dissimilar materials but the embedding of active components in order to deliver functionality that was not possible previously. Examples could include arbitrarily shaped electronics with integrated microfluidic thermal management and intelligent prostheses custom-fit to the anatomy of a specific patient. We review the state of the art in multiprocess (or hybrid) 3D printing, in which complementary processes, both novel and traditional, are combined to advance the future of manufacturing. © 2016, American Association for the Advancement of Science. All rights reserved.
Article
Development of high-performance p-type semiconductor based gas sensors exhibiting fast-response/recovery times with ultra-high response are of major importance for gas sensing applications. Recent reports demonstrated the excellent properties of p-type semiconducting oxide for various practical applications, especially for selective oxidation of volatile organic compounds (VOCs). In this work, sensors based on CuO nanowire (NW) networks have been successfully fabricated via a simple thermal oxidation process on pre-patterned Au/Cr pads. Our investigation demonstrates high impact of the process temperature on aspect ratio and density of copper oxide NWs. An optimal temperature for growth of thin and densely packed NWs was found to be at 425 °C. The fabricated sensors demonstrated ultra-high gas response by a factor of 313 to ethanol vapour (100 ppm) at an operating temperature of 250 °C. High stability and repeatability of these sensors indicate the efficiency of p-type oxide based gas sensors for selective detection of VOCs. A high-performance nanodevice was fabricated in a FIB-SEM system using a single CuO NW, demonstrating an ethanol response of 202 and rapid response and recovery of ~198 ms at room temperature. The involved gas sensing mechanism of CuO NW networks has been described. We consider that the presented results will be of a great interest for the development of higher-performance p-type semiconductor based sensors and bottom-up nanotechnologies.
Article
In this work, a new three-dimensional (3D) printing system based on liquid deposition modeling (LDM) is developed for the fabrication of conductive 3D nanocomposite-based microstructures with arbitrary shapes. This technology consists in the additive multilayer deposition of polymeric nanocomposite liquid dispersions based on poly(lactic acid) (PLA) and multi-walled carbon nanotubes (MWCNTs) by means of a home-modified low-cost commercial benchtop 3D printer. Electrical and rheological measurements on the nanocomposite at increasing MWCNT and PLA concentrations are used to find the optimal processing conditions and the printability windows for these systems. In addition, examples of conductive 3D microstructures directly formed upon 3D printing of such PLA/MWCNT-based nanocomposite dispersions are presented. The results of our study open the way to the direct deposition of intrinsically conductive polymer-based 3D microstructures by means of a low-cost LDM 3D printing technique.
Article
We describe the preparation and characterization of photo- and mechanochromic 3D printed structures using a commercial fused filament fabrication printer. Three spiropyran-containing poly(ɛ-caprolactone) (PCL) polymers were each filamentized and used to print single- and multi-component tensile testing specimens that would be difficult, if not impossible, to prepare using traditional manufacturing techniques. It was determined that the filament production and printing process did not degrade the spiropyran units or polymer chains, and that the mechanical properties of the specimens prepared with the custom filament were in good agreement with those from commercial PCL filament. In addition to printing photochromic and dual photo- and mechanochromic PCL materials, we also prepare PCL containing a spiropyran unit that is selectively activated by mechanical impetus. Multi-component specimens containing two different responsive spiropyrans enabled selective activation of different regions within the specimen depending on the stimulus applied to the material. By taking advantage of the unique capabilities of 3D printing, we also demonstrate rapid modification of a prototype force sensor that enables the assessment of peak load by simple visual assessment of mechanochromism.
Article
Metal oxides such as ZnO have been used as hydrogen sensors for a number of years. Through doping. the gas response of zinc oxide to hydrogen has been improved. Cadmium-doped ZnO nanowires (NWs) with high aspect ratio have been grown by electrodeposition. Single doped ZnO NWs have been isolated and contacted to form a nanodevice. Such nanosystem demonstrates an enhanced gas response and selectivity for the detection of hydrogen at room temperature compared to previously reported H-2 nanosensors based on pure single-ZnO NWs or multiple NWs. A dependence of the gas response of a single Cd-ZnO nanowire on the NW diameter and Cd content was observed. It is shown that cadmium-doping in single-crystal zinc oxide NWs can be used to optimize their response to gases without the requirement of external heaters. The sensing mechanisms responsible for such improved response to hydrogen are discussed.
Article
Vertically ordered nanotube array is a desirable configuration to improve gas sensing properties of the hematite which is the most abundant and cheapest metal oxide semiconductor on earth but has low and sluggish chemiresistive responses. We have synthesized a vertically aligned, highly ordered hematite nanotube array directly on a patterned SiO2/Si substrate and then it used as a gas sensor without additional processing. The nanotube array sensor shows unprecedentedly ultrahigh and selective responses to acetone with detection limits down to a few parts per billion and response time shorter than 3 s.
Article
Mixtures of WO3 and Cr2O3 in varying weight ratios as well as adjacent alignment of these two powders were both examined as possible designs for NO-selective sensor. Studies focused on resistance measurements toward NO and CO at 300 °C were carried out. Using the sensor design with the adjacent alignment of n-type WO3 and p-type Cr2O3 resulted in optimal performance. This sensor design exploits the different majority carriers in these two semiconducting oxides for selective NO gas sensing. The advantage of such a sensor system is that the device can be sensitive to NO at low ppb level (18 ppb detection limit) and discriminate against CO at concentrations a thousand-fold higher (20 ppm). The sensing mechanism was investigated by in situ diffuse reflectance infrared studies. Characterization of the adjacent p–n interface was done by scanning electron microscopy (SEM) and Raman imaging study. Practical application of this device is demonstrated by measuring NO in human breath samples.
Article
Since the ancient discovery of the 'sweet odor' in human breath gas, pursuits of the breath analysis-based disease diagnostics have never stopped. Actually, the 'smell' of the breath, as one of three key disease diagnostic techniques, has been used in Eastern-Medicine for more than three thousand years. With advancement of measuring technologies in sensitivity and selectivity, more specific breath gas species have been identified and established as a biomarker of a particular disease. Acetone is one of the breath gases and its concentration in exhaled breath can now be determined with high accuracy using various techniques and methods. With the worldwide prevalence of diabetes that is typically diagnosed through blood testing, human desire to achieve non-blood based diabetic diagnostics and monitoring has never been quenched. Questions, such as is breath acetone a biomarker of diabetes and how is the breath acetone related to the blood glucose (BG) level (the golden criterion currently used in clinic for diabetes diagnostic, monitoring, and management), remain to be answered. A majority of current research efforts in breath acetone measurements and its technology developments focus on addressing the first question. The effort to tackle the second question has begun recently. The earliest breath acetone measurement in clearly defined diabetic patients was reported more than 60 years ago. For more than a half-century, as reviewed in this paper, there have been more than 41 independent studies of breath acetone using various techniques and methods, and more than 3211 human subjects, including 1581 healthy people, 242 Type 1 diabetic patients, 384 Type 2 diabetic patients, 174 unspecified diabetic patients, and 830 non-diabetic patients or healthy subjects who are under various physiological conditions, have been used in the studies. The results of the breath acetone measurements collected in this review support that many conditions might cause changes to breath acetone concentrations; however, the results from the six independent studies using clearly-defined Type 1 and Type 2 diabetic patients unanimously support that an elevated mean breath acetone concentration exists in Type 1 diabetes. Note that there is some overlap between the ranges of breath acetone concentration in individual T1D patients and healthy subjects; this reminds one to be careful when using an acetone breath test on T1D diagnostics. Comparatively, it is too early to draw a general conclusion on the relationship between a breath acetone level and a BG level from the very limited data in the literature.
Article
Internal oxidized copper was tested by isothermal mechanical spectroscopy in a medium temperature range (300 600 K). Experimental results show the existence of a non-thermally activated effect at low temperature and of a relaxation peak at higher temperatures. The material microstructure was studied by combination of Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectrometry (EELS). The TEM study allowed us to investigate the distribution of fine spherical particles and the presence of particular network dislocations inside the grains. The EELS method was used to identify the nature of these fine particles as Cu{2}O. The internal friction has revealed a non thermally activated maximum occurring at 0.1 Hz for temperatures ranging from 290 K to 394 K, and a relaxation peak obtained after annealing at 573 K. This peak is stable after successive annealings at 723 K and 873 K. Comparison of the microstructure observations, their evolution with annealing and the evolution of the relaxation effect with annealing temperature enables us to interpret the phenomena described in this work: on the one hand, the microstructural characterisation using TEM and EELS allows us to assign the first effect to the result of a transformation of metastable Cu{2}O particles to CuO under the cyclic stress; on the other hand, the relaxation peak that does not change after high temperature annealing is linked with a particular stable dislocation network observed in many grains.
Article
We observed two long-range-ordering structures of oxygen vacancies, one in every tenth plane of (33̅0) and another in every fourth plane of (11̅2) in α-Fe2O3 nanowires and nanobelts synthesized under the same conditions. Interestingly, both types of oxygen-vacancy structures found in different nanowires have an equivalent ordering distance of 1.45 or 1.47 nm and were parallel to the growth direction of the nanowires and nanobelts. Lattice mismatch induced strain at the growth temperatures seems to justify the observed vacancy-ordering distance and may explain the reason for occurrence of such oxygen-vacancy ordering in various metal oxide nanowires grown from using both foils and catalyst clusters.
Article
Tin dioxide is a widely used sensitive material for gas sensors. Many research and development groups in academia and industry are contributing to the increase of (basic) knowledge/(applied) know-how. However, from a systematic point of view the knowledge gaining process seems not to be coherent. One reason is the lack of a general applicable model which combines the basic principles with measurable sensor parameters.The approach in the presented work is to provide a frame model that deals with all contributions involved in conduction within a real world sensor. For doing so, one starts with identifying the different building blocks of a sensor. Afterwards their main inputs are analyzed in combination with the gas reaction involved in sensing. At the end, the contributions are summarized together with their interactions.The work presented here is one step towards a general applicable model for real world gas sensors.
Article
Although it has been known for centuries that there are compounds in exhaled breath that are altered in disease, it is only in the last few decades that it has been possible to measure them with sufficient accuracy and precision to make them clinically useful. The clinical utility of breath analysis has also been limited by the practical difficulties of collecting representative breath samples, free from contaminants. More recent methods of breath analysis have allowed real-time analysis of breath, eliminating the need for sample collection, and therefore potentially allowing the rapid feedback of results to patient and clinician. One possible future application of breath analysis may be the monitoring of metabolic control in patients with diabetes mellitus. This perspective article provides an overview of the studies of breath analysis in diabetes, focusing on the breath metabolites; acetone, isoprene and also methyl nitrate that have previously been reported to be altered in diabetes, highlighting the factors that may potentially confound their interpretation. Specific attention is given to selected ion flow tube mass spectrometry (SIFT-MS) and proton transfer reaction mass spectrometry (PTR-MS), because they are techniques that have been developed specifically for the absolute quantification of breath metabolites in real time, although reference is made to some of the alternative techniques, including sensors and optical devices. Whilst breath analysis, using SIFT-MS, PTR-MS and other sensitive techniques, can potentially be used for the non-invasive monitoring of metabolic conditions that may include diabetes mellitus, further work is required in terms of the clinical and analytical validation. Furthermore, it is unclear at present what breath metabolites should be monitored and what factors may confound their interpretation. Although a non-invasive method of monitoring glycaemic control is clearly desirable, it will be important to demonstrate its analytical comparability with the well-established and validated methods for blood glucose measurement.
Article
The Diabetes Fear of Injecting and Self-Testing Questionnaire (D-FISQ) has been validated in the adult population (1–4), but there is no reliable tool to assess needle fear in the pediatric population with type 1 diabetes. Our objectives were to demonstrate the reliability of the D-FISQ in the pediatric type 1 diabetic population, to evaluate the prevalence of needle fear, and to determine the ability of medical care providers to identify needle fear. Patients aged 2–21 years with type 1 diabetes were eligible to participate if they had a diabetes duration of >1 month, took insulin by injection, and were English speaking. Exclusion criteria included being a ward of the state, using continuous subcutaneous insulin infusion therapy, and not having a parent/legal guardian present. Potential subjects were approached by study personnel at regularly scheduled clinic visits, and consent was obtained. The study was approved by the institutional review board. The D-FISQ was administered to each subject and his/her parent or guardian. The D-FISQ is a 30-item self-report questionnaire consisting of two subscales that measure fear of self-injecting (FSI) and fear of self-testing (FST), the latter measuring fear of blood glucose testing (1). The D-FISQ was administered to each parent and each child as follows. If the child self-administered his/her own injections and/or …