Fabrication of Low-Cost Miniaturized Gas Cells via SLA 3D-Printing for UV-Based Gas Sensors.

This paper reports recent development and application of optical fiber gas sensors using absorption spectroscopy, including open-path gas sensors using fiber coupled micro-optic cells and photonic bandgap (PBG) fibers. A fiber-optic sensor system capable of detecting dissolved fault gases in oil-insulated equipment in power industry is presented. The gases include methane (CH 4 ), acetylene (C 2 H 2 ) and ethylene (C 2 H 4 ). In addition, the development of gas sensor using PBG fiber will be reported. Keywords: optical fiber gas sensor, dissolved gas measurement, photonic bandgap fiber. 1. INTRODUCTION Absorption based optical spectroscopy [1] is widely used in conventional gas analysis. As the rapid development of optical fiber technology, the optical fiber sensors based on these techniques have attracted significant attention because of their importance in applications such as environmental monitoring, biomedical sensing, and industrial process control. The advantages of fiber sensors include their remote detection capability, safety in hazardous environments and immunity to electromagnetic fields. A number of important gases which possess overtone or combination absorption lines in the low-loss transmission window of silica fibers may be detected with fiber optic systems. Early fiber optic gas sensors made use of open path, bulk gas cells and LED sources with optical fibers for light transmission to and from the cell where light absorption took place whic h resulting in relative low detection se nsitivity. Sensitivity and selectivity can be significantly enhanced by use of single frequency laser sources such as distributed feedba ck (DFB) lasers and external cavity diode (ECD) lasers [2-5]. The laser sources have very high spectral power densities within a spectral width less than that of a single absorpti on line in the absorption spectrum. Selectivity can be assured by tuning the laser wavelength to an absorption line of the gas being measured through the us e of a reference gas cell [3,5]. The use of the high spectral density DFB/ECD lasers allowed the demonstration of high se nsitivity gas detection with relatively simple micro-optic gas cells [6-8]. For such kind of gas sensors, there is a variety of applications in industry. Recently, we have developed a fiber optic multi-gas detection system for monitoring the dissolved fault gases in oil-filled power equipment. In power systems, there is a number of oil-insulated power equipment such as power transformers which are im portant and valuable assets. Suitable and frequent maintenance is a prerequisite to ensure the reliability. However, in order to save the maintenance .

A novel double spot-ring plane-concave multipass cell (DSPC-MPC) gas sensor was proposed for simultaneous detection of trace gases, which has lower cost and higher mirror utilization than the traditional multipass cell with 129 m, 107 m, 85 m, 63 m and 40 m effective optical path lengths adjustable. The performance of the DSPC-MPC gas sensor was evaluated by measuring CO and CH4 using two narrow linewidth distributed feedback lasers with center wavelengths of 1567 nm and 1653 nm, respectively. An adjustable digital PID laser frequency stabilization system based on LabVIEW platform was developed to continuously stabilize the laser frequency within ∼±30.3 MHz. The Allan deviation results showed that the minimum detection limits for CO and CH4 were 0.07 ppmv and 0.008 ppmv at integration times of 711 s and 245 s, respectively. The proposed concept of DSPC-MPC provides more ideas for the realization of gas detection under different absorption path lengths and the development of multi-component gas sensing systems.

Gas sensors are key elements in many applications that affect the quality of our natural life as well as the efficiency of industrial production. In many of these applications, multiple gases must be monitored simultaneously over a long period of time with minimal maintenance and in different locations. For such features to exist, optical techniques are the best candidates. For these reasons, spectroscopic gas sensors have gained both academic and industrial interest in the last few years. Optical spectroscopic sensors are not in direct contact with the measured gases, and they are usually able to detect and quantify a wide range of gases simultaneously, depending on their spectral range. A Fourier transform infrared (FTIR) spectrometer is a good example of a device that can satisfy most of these required features. However, a FTIR spectrometer is usually a desktop instrument with high cost and weight; it also needs calibration and readjustment. The recent development in this domain using new technologies, such as the microelectromechanical systems (MEMS) technology, can overcome such obstacles as demonstrated in the literature in the last two decades. This technology provides the necessary compactness and low production cost. This Spotlight is focused on using a MEMS FTIR spectrometer as a core building block in optical gas sensing. The micro-optical bench technology used for this development is discussed, followed by presenting the basics of the sensing technique. Then an overview of the system components and their state of the art is given including the light source, the miniaturized interferometer and gas cell, the optical connectivity, and the detection for both the near-infrared (NIR) and the mid-infrared (MIR) spectral ranges. A comparison is carried out showing the pros and cons of each range accounting for the absorption cross sections of the gases and the noise performance of the system components. Next, the impact of the limitation in the signal-to-noise ratio (SNR) and spectral resolution due to miniaturization on the gas sensor performance is discussed. Then, an experimental setup to evaluate the sensor performance and extract its sensitivity is explained and the experimental results for detecting acetylene (C2H2) and carbon dioxide (CO2) gases are presented as examples. Finally, this Spotlight is concluded by a discussion on the foreseen challenges and a summary of the work done in this direction.

The MEMS gas sensor is one of the most promising gas sensors nowadays due to its advantage of small size, low power consumption, and easy integration. It has been widely applied in energy components, portable devices, smart living, etc. The performance of the gas sensor is largely determined by the sensing materials, as well as the fabrication methods. In this review, recent research progress on H2, CO, NO2, H2S, and NH3 MEMS sensors is surveyed, and sensing materials such as metal oxide semiconductors, organic materials, and carbon materials, modification methods like construction of heterostructures, doping, and surface modification of noble metals, and fabrication methods including chemical vapor deposition (CVD), sputtering deposition (SD), etc., are summarized. The effect of materials and technology on the performance of the MEMS gas sensors are compared.

BackgroundTemporary implant-retained restorations are required to support function and esthetics of the masticatory system until the final restoration is completed and delivered. Acrylic resins are commonly used in prosthetic dentistry and lately they have been used in three-dimensional (3D) printing technology. Since this technology it is fairly new, the number of studies on their susceptibility to microbial adhesion is low. Restorations placed even for a short period of time may become the reservoir for microorganisms that may affect the peri-implant tissues and trigger inflammation endangering further procedures. The aim of the study was to test the biofilm formation on acrylamide resins used to fabricate temporary restorations in 3D printing technology and to assess if the post-processing impacts microbial adhesion.MethodsDisk-shaped samples were manufactured using the 3D printing technique from three commercially available UV-curable resins consisting of acrylate and methacrylate oligomers with various time and inhibitors of polymerization (NextDent MFH bleach, NextDent 3D Plus, MazicD Temp). The tested samples were raw, polished and glazed. The ability to create biofilm by oral streptococci (S. mutans, S. sanguinis, S. oralis, S. mitis) was tested, as well as species with higher pathogenic potential: Staphylococcus aureus, Staphylococcus epidermidis and Candida albicans. The roughness of the materials was measured by an atomic force microscope. Biofilm formation was assessed after 72 h of incubation by crystal violet staining with absorbance measurement, quantification of viable microorganisms, and imaging with a scanning electron microscope (SEM).ResultsEach tested species formed the biofilm on the samples of all three resins. Post-production processing resulted in reduced roughness parameters and biofilm abundance. Polishing and glazing reduced roughness parameters significantly in the NextDent resin group, while glazing alone caused significant surface smoothing in Mazic Temp. A thin layer of microbial biofilm covered glazed resin surfaces with a small number of microorganisms for all tested strains except S. oralis and S. epidermidis, while raw and polished surfaces were covered with a dense biofilm, rich in microorganisms.ConclusionsUV-curing acrylic resins used for fabricating temporary restorations in the 3D technology are the interim solution, but are susceptible to adhesion and biofilm formation by oral streptococci, staphylococci and Candida. Post-processing and particularly glazing process significantly reduce bacterial biofilm formation and the risk of failure of final restoration.

Reagent-less and sub-minute quantification of sulfite in food samples using substrate-integrated hollow waveguide gas sensors coupled to deep-UV LED

Ga2O3 has emerged as a promising ultrawide bandgap semiconductor for numerous device applications owing to its excellent material properties. In this paper, we present a comprehensive review on major advances achieved over the past thirty years in the field of Ga2O3-based gas sensors. We begin with a brief introduction of the polymorphs and basic electric properties of Ga2O3. Next, we provide an overview of the typical preparation methods for the fabrication of Ga2O3-sensing material developed so far. Then, we will concentrate our discussion on the state-of-the-art Ga2O3-based gas sensor devices and put an emphasis on seven sophisticated strategies to improve their gas-sensing performance in terms of material engineering and device optimization. Finally, we give some concluding remarks and put forward some suggestions, including (i) construction of hybrid structures with two-dimensional materials and organic polymers, (ii) combination with density functional theoretical calculations and machine learning, and (iii) development of optical sensors using the characteristic optical spectra for the future development of novel Ga2O3-based gas sensors.

The significant air pollution caused mainly by exhaust and factory emissions has become a considerable hazard to human survival and development [1]. Nitrogen oxides (NOx) are a family of poisonous and highly reactive gases which forming at fuel high temperatures burn [2]. As an industrial source, such as power plants, industrial boilers, cement kilns, and turbines, NOx pollution is emitted by automobiles, trucks and various non-road vehicles (e.g., construction equipment, boats, etc.) [3]. Hazardous compounds such as NOx with negative environmental and human health consequences, must be controlled to avoid ecological disasters [4]. Metal-oxide-semiconductors (MOSs) as a class of chemoresistive sensors have attracted great attention in environmental monitoring, automotive emission monitoring and food safety testing, due to their low production cost, high sensitivity, simplicity of use and their ability to detect various gases [5].Due to its inherent advantages in charge carrier mobility, chemical activity, and redox potential, TiO2 (n-type) is a widely used and extensively researched MOSs. At the same time, CuO is also known to be an active transition-metal based semiconductor (p-type) having a lower electrical resistance value as well as a narrow band gap. A promising strategy for improving the gas sensitivity at room temperature (RT) is to apply p-n heterostructures to modulate resistance more strongly. The active surface area and nanoarchitecture affect the gas sensors' sensitivity. The provision of porous MOSs nanostructures to improve the diffusion channel and increase the adsorption of target gas molecules is the most promising means of achieving enhanced sensitivity [6-7]. The mentioned structures may be created using the glancing angle deposition (GLAD) reactive magnetron sputtering method. The TiO2/CuO heterostructure gas sensors were synthesized by reactive magnetron sputtering using the GLAD. The application CuO layer improves the gas sensor device's sensitivity due to electron-hole pair recombination and a reduction in the concentration of charge carriers in the TiO2 and CuO layers. The identical circumstances of 10 ppm and RT were used for each gas selectivity test. It demonstrates the potential of using heterostructured CuO/TiO2 nanorods as N2O gas sensors. Dynamic gas response analysis shows that the response time is only 47s, whereas the recovery time is 80s. The dynamic gas sensing measurements at various N2O gas concentrations exhibit excellent linearity at 50 ppb to 5 ppm range. The sensor's gas response was 2% at a very low N2O concentration (50 ppb) and 9.8% at 5 ppm. Thus, the research findings indicate that the p-n heterostructured CuO/TiO2 nanorods synthesized by reactive magnetron sputtering using the glancing angle deposition show fast response and recovery times in ultra-low N2O gas concentration in RT. It can be used as excellent N2O gas sensors for quickly monitoring air pollution. Acknowledgements. This research has been funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP13067814) and Nazarbayev University under the Collaborative Research Program (Grant No. 021220CRP0122). References Zhu, L., Zeng, W. Room-temperature gas sensing of ZnO-based gas sensor: A review // Sensors and Actuators A: Physical. – 2017. №267. –P. 242-261. https://doi.org/10.1016/j.sna.2017.10.021.Bhati, V., Hojamberdiev, M., & Kumar, M. The enhanced sensing performance of ZnO nanostructures-based gas sensors: A review // Energy Reports – 2019. №6. P. – 46-62. https://doi.org/10.1016/j.egyr.2019.08.070.Daryakenari, A., Apostoluk, A., & Delaunay, J. Effect of Pt decoration on the gas response of ZnO nanoparticles // Physica Status Solidi (C). – 2012. №10(10). P. – 1297-1300. https://doi.org/10.1002/pssc.201200937H.B. Kim, S.P. Eckel, J.H. Kim, F.D. Gilliland, Exhaled NO: determinants and clinical application in children with allergic airway disease Allergy Asthma Immunol Res, 8 (2016), pp. 12-21Dae-Sik Lee, Jun-Woo Lim, Sang-Mun Lee, Jeung-Soo Huh, Duk-Dong Lee, Fabrication and characterization of micro-gas sensor for nitrogen oxides gas detection, Sensors and Actuators B: Chemical, Volume 64, Issues 1–3, 10 June 2000, Pages 31-36M. Chen, Z. Wang, D. Han, F. Gu, G. Guo, Porous ZnO Polygonal Nanoflakes: Synthesis, Use in High-Sensitivity NO 2 Gas Sensor, and Proposed Mechanism of Gas Sensing, J. Phys. Chem. C. 115 (2011) 12763–12773. https://doi.org/10.1021/jp201816d.L. Van Duy, N. Van Duy, C.M. Hung, N.D. Hoa, N.Q. Dich, Urea mediated synthesis and acetone-sensing properties of ultrathin porous ZnO nanoplates, Mater. Today Commun. 25 (2020) 101445. https://doi.org/10.1016/j.mtcomm.2020.101445.

Introduction Gas sensors with high flexibility and favorable extensibility have increasingly attractive prospects. Conventional rigid ceramics or semiconductor-based gas sensors have restricted flexibility and ductility, limiting their use in flexible devices and wearable electronics. Flexible gas sensors possess broad application prospects in the fields of wearable electronics, artificial intelligence, medical health, etc. Two-dimensional (2D) layered nanomaterials have attracted attention due to unique properties, which possess tunable band gaps and excellent mobility inherently. For example, graphene is usually utilized as gas sensing material due to high specific surface area and high carrier mobility [1]. However, the properties of pristine graphene nanoplatelets (GNPs) are influenced by significant adsorption of oxygen in an air environment, leading to instability and carrier mobility recession, limiting the practical application of GNPs gas sensors in atmosphere. The combination of quantum dots or nanobelts and 2D materials could build sensitized nanocomposites, which improves sensing performance of gas sensors. Flexible and ultrafast-response nitrogen dioxide (NO2) gas sensors based on cotton fibre that applies the mechanism of coupling and hydrogen bonding interaction were prepared by facile layered dip-coating methods. The gas sensors were fabricated utilizing cotton fibre as flexible substrate and bismuth sulfide (Bi2S3) nanobelts-sensitized GNPs nanocomposites as sensing layer. The flexible gas sensing fibre demonstrated ultrafast and recoverable response (67 s/45 s for 500 ppb gas), good reproducibility and mechanical robustness. The favorable sensing performance and high flexibility of fibre gas sensors will open potential prospects in intelligent sensing system and wearable electronics. Experimental Preparation of coupling reagent modified cotton fibre: The cleansed fibre substrate was first modified by 3-aminopropyl) triethoxysilane (APTES: coupling reagent) via dipping in APTES ethanol solution, and then rinsed with deionized water and dried in drying oven (100 ℃, 15 min). The organic functional group in coupling agent can be combined with the fiber substrate, meanwhile the silanoxy group in coupling agent is reactive with inorganic substances. When coupling agent is positioned between fiber substrate and gas sensing layer, bonding structure of cotton fibre-coupling agent-sensing layer can be formed. Synthesis of Bi2S3 nanobelts-sensitized graphene nanoplatelets nanocomposites: Solvothermal method was used for Bi2S3 nanobelts synthesis reported in literatures [2]. And GNPs/Sodium laurylsulfonate (SDL) ethanol solution (solution A) and Bi2S3/polyethylene glycol (PEG) ethanol solution (solution B) were prepared for next synthesis. Finally, solution A were injected into solution B under magnetic stirring for six hours to prepare Bi2S3/GNPs nanocomposites. Flexible gas sensor fabrication: The modified fibre was dipped in Bi2S3/GNPs solution for 30 min through dip-coating method, then treated with Pb(NO3)2 for surface ligand exchange to remove insulating organic ligands capping on Bi2S3 surface, lastly annealed in drying oven (60 ℃, 30 min). Results and Conclusions The stereoscopic illustration of electronic fibre gas sensor is shown in figure 1 (a). After two steps dip-coating processes, modified layer and outer Bi2S3/GNPs nanocomposites layer were successively coated on the surface of cotton fibre. Figure 1 (b) shows cross-section structure of fiber-based gas sensors, illustrating bonding structure of fibre-coupling agent-sensing layer. As for Bi2S3/GNPs nanocomposites layer, the intermolecular hydrogen bond [3] between sulfonic groups (-SO3H) of SDL and hydroxyl groups (-OH) of PEG could contribute to the interfacial adhesion between substrate and sensing layer (figure 1 (c)). For one thing, cotton fiber has advantages of large specific surface area and rich skeletal structure, which helps the combination of fiber skeleton and sensing materials. For another, Bi2S3-sensitized GNPs nanocomposites constructed an excellent receptor-transducer gas-sensing layer. Considering the dual-mode characteristics of fast carrier transfer on graphene and strong adsorption of gas molecules in Bi2S3 nanobelts, fiber-based gas sensors demonstrated ultrafast and recoverable response (67 s/45 s for 500 ppb gas), good reproducibility and mechanical robustness (figure 1(f-g)). The device showed excellent reversibility and negligible baseline drift following cycling responses (figure 1(g)). Compared with recently reported fibre-based gas sensors (Figure 1(h)), fibre-based gas sensors showed significantly enhanced response and recovery time. This work indicates that the flexible gas sensing fibre could be used to establish wearable electronics and real-time atmosphere information monitoring system.

In this paper, the authors present a physical model developed to simulate accurate external ventricular drain (EVD) placement with realistic haptic and visual feedbacks to serve as a platform for complete procedural training. Insertion of an EVD via ventriculostomy is a common neurosurgical procedure used to monitor intracranial pressures and/or drain CSF. Currently, realistic training tools are scarce and mainly limited to virtual reality simulation systems. The use of 3D printing technology enables the development of realistic anatomical structures and customized design for physical simulators. In this study, the authors used the advantages of 3D printing to directly build the model geometry from stealth head CT scans and build a phantom brain mold based on 3D scans of a plastinated human brain. The resultant simulator provides realistic haptic feedback during a procedure, with visualization of catheter trajectory and fluid drainage. A multiinstitutional survey was also used to prove content validity of the simulator. With minor refinement, this simulator is expected to be a cost-effective tool for training neurosurgical residents in EVD placement.

This project aims to develop a 3D printed robotic arm that uses an Arduino microcontroller and a gas sensor to remove blockages in drainage systems. The arm is designed to navigate through narrow pipes and use a combination of suction and manipulation to remove debris and blockages. The arm is controlled by an embedded system, which utilizes the Arduino microcontroller and gas sensor to detect the presence of blockages and trigger the necessary actions to remove them. The use of 3D printing technology allows for the creation of a lightweight, compact and customizable arm, while the gas sensor enables the system to detect blockages in real-time. This system has several advantages over the traditional methods of sewage blockage detection and clearance. This system reduces the need for human intervention and makes the system safer for workers. It is also more versatile and can be used in variety of environments.

The development of a compact iHWG-ICL gas sensor combining innovative substrate-integrated hollow waveguides (iHWG) with mid-infrared emitting type-II interband cascade lasers (ICL) is presented. Hence, tunable laser absorption spectroscopy (TLAS) with iHWGs in direct absorption mode is enabled. Using a room-temperature distributed feedback (DFB) ICL emitting at approximately 3.366 μm, quantitative sensing of methane was demonstrated. Wavelength scanning was obtained via current tuning for monitoring an isolated line in the v3 fundamental band of CH4. The obtained spectra were compared to calculated spectra derived from the HITRAN2012 database. Furthermore, the performance of iHWGs simultaneously serving as miniaturized gas cell and as efficient optical waveguide at various absorption path lengths was tested and optimized. Calibration functions in the concentration range of 50 to 400 ppmv were established enabling limits of detection ranging from 6 to 28 ppmv. Hence, the combination of iHWGs with ICLs fac...

Performance improvement of MOCVD grown ZnGa2O4 based NO gas sensors using plasma surface treatment

Nanoparticles anchored strategy to develop 2D MoS2 and MoSe2 based room temperature chemiresistive gas sensors

Strain-Assisted Single Pt Sites on High-Curvature MoS ₂ Surface for Ultrasensitive H ₂ S Sensing