Compact Yttria-Stabilized Zirconia Based Total NOx Sensor with a Dual Functional Co3O4/NiO Sensing Electrode

Mixed Potential Type Isoprene Sensor for the Application in Real-Time Monitoring of Biomarker Gases

Monitoring of isoprene in exhaled breath is expected to provide a noninvasive and painless method for dynamic monitoring of physiological and metabolic states during exercise. However, for real-time and portable detection of isoprene, gas sensors have become the best choice for gas detection technology, which are crucial to achieving the goal of anytime, anywhere, human-centered healthcare in the future. Here, we first report a mixed potential type isoprene sensor based on a Gd2Zr2O7 solid electrolyte and a CdSb2O6 sensing electrode, which enables sensitive detection for isoprene with sensitivities of -21.2 mV/ppm and -65.8 mV/decade in the range of 0.05-1 and 1-100 ppm. The sensing behavior of the sensor follows the mixed potential sensing mechanism and was further verified by the electrochemical polarization curves. The significant differentiation between the sensor response to exhaled breath of healthy individuals and simulated breath containing different concentrations of isoprene demonstrates the potential of the sensor for the detection of isoprene in exhaled breath. Simultaneously, monitoring of isoprene during exercise signifies the feasibility of the sensor in dynamic monitoring of physiological indicators, which is not only of great significance for optimizing training and guiding therapeutic exercise intervention in sporting scenarios but also expected to help further reveal the interaction between exercise, muscle, and organ metabolism in medicine.

Opportunities of Electronic and Optical Sensors in Autonomous Medical Plasma Technologies

Low temperature plasma technology is proving to be at the frontier of emerging medical technologies with real potential to overcome escalating healthcare challenges including antimicrobial and anticancer resistance. However, significant improvements in efficacy, safety, and reproducibility of plasma treatments need to be addressed to realize the full clinical potential of the technology. To improve plasma treatments recent research has focused on integrating automated feedback control systems into medical plasma technologies to maintain optimal performance and safety. However, more advanced diagnostic systems are still needed to provide data into feedback control systems with sufficient levels of sensitivity, accuracy, and reproducibility. These diagnostic systems need to be compatible with the biological target and to also not perturb the plasma treatment. This paper reviews the state-of-the-art electronic and optical sensors that might be suitable to address this unmet technological need, and the steps needed to integrate these sensors into autonomous plasma systems. Realizing this technological gap could facilitate the development of next-generation medical plasma technologies with strong potential to yield superior healthcare outcomes.

Macroporous SnO2/MoS2 inverse opal hierarchitecture for highly efficient trace NO2 gas sensing

The innovation of NO₂ gas sensors is highly desirable in environmental monitoring and human safety. Herein, a macroporous SnO₂/MoS₂ inverse opal hierarchitecture has been constructed with substantial interface charge transfer, which realizes the efficient and stable detection of NO₂ with an enhanced response, fast kinetics, and high selectivity at low temperatures.

Promoted Carbon Monoxide Sensing Performance of a Bi2Mn4O10-Based Mixed-Potential Sensor by Regulating Oxygen Vacancies

The YSZ-based mixed-potential sensor has exhibited promising application prospects for in situ carbon monoxide (CO) monitoring owing to its excellent thermal stability. However, the way to further enhance the sensitivity and selectivity of the sensor remains challenging due to the limitation of the sensing material. In the present work, we proposed a strategy of introducing moderate oxygen vacancies in the transition metal oxide sensing material to enhance CO sensing performance. More importantly, the oxygen vacancies of the sensing electrode were regulated by adjusting the volatilization of the Bi element at different sintering temperatures. Meanwhile, the stable mullite structure and variable valency of Mn were also exploited to maintain the phase structure stability and charge balance brought by the loss of Bi. The relationship between CO sensing properties and the proportion of both Mn³⁺/Mn⁴⁺ and oxygen vacancies was elucidated from XPS and EIS measurements. By contrast, the 800 °C-sintered Bi₂Mn₄O₁₀ possesses the highest oxygen vacancy content and thus exhibits preferable sensing performance including a lower detecting limit (10 ppm), swifter response/recovery processes, and enhanced CO sensitivity (-70.47 mV/decade operated at 450 °C) with satisfactory selectivity and stability, indicating a promising prospect for CO monitoring under exhaust environments.

Cascading Photoelectric Detecting and Chemiresistive Gas-Sensing Properties of Pb5 S2 I6 Nanowire Mesh for Multi-Factor Accurate Fire Alarm

Accurate fire warning is very important for people's life and property safety. The most commonly used fire alarm is based on the detection of a single factor of gases, smoke particles, or temperature, which easily causes false alarm due to complex environmental conditions. A facile multi-factor route for fabricating an accurate analog fire alarm using a Pb₅ S₂ I₆ nanowire mesh based on its photoelectric and gas-sensing dual function is presented. The Pb₅ S₂ I₆ nanowire mesh presents excellent photoelectric detection capabilities and is sensitive to ppm-level NO₂ at room temperature. Under the "two-step verification" circuit of light and gas factors, the bimodal simulation fire alarm based on this Pb₅ S₂ I₆ nanowire mesh can resist the interference of complex environmental factors and effectively reduce the false alarm rate.

Flexible All-Inorganic Room-Temperature Chemiresistors Based on Fibrous Ceramic Substrate and Visible-Light-Powered Semiconductor Sensing Layer

As the most extensively used gas-sensing devices, inorganic semiconductor chemiresistors are facing great challenges in realizing mechanical flexibility and room-temperature gas detection for developing next-generation wearable sensing devices. Herein, for the first time, flexible all-inorganic yttria-stabilized zirconia (YSZ)/In2 O3 /graphitic carbon nitride (g-C3 N4 ) (ZIC) gas sensor is designed by employing YSZ nanofibers as substrate, and ultrathin In2 O3 /g-C3 N4 heterostructures as active sensing layer. The YSZ substrate possesses small nanofiber diameter (310 nm), ultrafine grain size (23.9 nm), and abundant dangling bonds, endowing it with striking mechanical flexibility and strong adhesion with In2 O3 /g-C3 N4 sensing layer. Meanwhile, the ultrathin thickness (≈7 nm) of In2 O3 /g-C3 N4 ensures that the inorganic sensing layer has tiny linear strain along with the deformation of flexible YSZ substrate, thereby enabling unusual bending capacity. To address the operating temperature issue, the gas sensor is operated by using a visible-light-powered strategy. Under visible-light illumination, the flexible ZIC sensor exhibits a perfectly reversible response/recovery dynamic process and ultralow detection limit of 50 ppb to toxic nitrogen dioxide at room temperature. This work not only provides an insight into the mechanical flexibility of inorganic materials, but also offers a valuable reference for developing other flexible inorganic-semiconductor-based room-temperature gas sensors.

Machine Learning-Assisted Development of Sensitive Electrode Materials for Mixed Potential-Type NO2 Gas Sensors

Yttrium-stabilized zirconia (YSZ)-based mixed potential-type NO_x sensors have broad application prospects in automotive exhaust gas detection. Great efforts continue to be made in developing high-performance sensitive electrode materials for mixed potential-type NO₂ gas sensors. However, only five kinds of new sensing electrode materials have been developed for this type of gas sensor in the last 3 years. In this work, four different tree-based machine learning models were trained to find potentially sensitive electrode materials for NO₂ detection. More than 400 materials were selected from 8000 materials by the above machine learning models. To further verify the reliability of the model, 13 of these materials containing unexploited elements were selected as sensitive electrode materials for making sensors and testing their gas-sensing performances. The experimental results showed that all 13 materials exhibited good gas-sensing performance for NO₂. More interestingly, an electrode material BPO₄, which does not contain any metal elements, was also screened out and showed good sensing properties to NO₂. In a short period of time, 13 new sensitive electrode materials for NO₂ detection were targeted and screened, which was difficult to achieve by a trial-and-error procedure.

Battery-Sensor Hybrid: A New Gas Sensing Paradigm with Complete Energy Self-Sufficiency

Fully autonomous operation has long been an ultimate goal in environmental sensing. Although self-powered gas sensors based on energy harvesting have been widely reported to provide power for autonomous operation, these sensors rely on external sources of harvestable energy, thus are not completely self-sufficient. Herein, a battery-sensor hybrid device that can simultaneously function as both a power source and a gas sensor is presented. The battery-sensor consists of a cathode that reduces NO₂ to NO₂^- via a catalyst with Fe-N_x species distributed on highly graphitic porous nitrogen-doped carbon. On the basis of the efficient and selective electrocatalytic activity of the catalyst, the battery-sensor is capable of sensing NO₂ and does so without any external power, overcoming the long-standing grand challenge to achieve complete energy self-sufficiency. Furthermore, through controlling the working current the sensing range can be significantly expanded and electronically tuned, which is not only unprecedented for gas sensors but also of remarkable commercial practicality. The proposed battery-sensor hybrid architecture represents a new paradigm toward sensors with complete energy self-sufficiency.

Fast detection of NO2 by porous SnO2 nanotoast sensor at low temperature

In order to challenge high working temperature, low response and low selectivity of present NO₂ sensor, porous SnO₂ nanotoasts with a large surface area (79.94 m²/g) were synthesized. Thick film sensors fabricated by the SnO₂ nanotoasts exhibited a high response to NO₂ gas operating at room temperature. Excellent performance for NO₂ sensing gas at 50 °C, included the high response of 105.2 (10 ppm), low detection limitation of 0.1 ppm, fast response within 10 s, and wide range of 0.1-10 ppm (R² = 0.9931). These sensors also demonstrated perfect selectivity, moisture resistance and 90 days of long-term stability. SnO₂ nanotoasts sensor has excellent detection ability in actual detection. The superior response of porous SnO₂ nanotoasts towards NO₂ was attributed to the special porous structure with large specific surface area and oxygen vacancies in sensing material, which helped adsorption of the target gas molecules onto the sensing surfaces and transfer of the charge.