High-Performance Wearable Sensor Inspired by the Neuron Conduction Mechanism through Gold-Induced Sulfur Vacancies

Sulfur vacancy-rich bismuth sulfide nanowire derived from CAU-17 for radioactive iodine capture in complex environments: Performance and intrinsic mechanisms

Effective capture and immobilization of volatile radioiodine from the off-gas of post-treatment plants is crucial for nuclear safety and public health, considering its long half-life, high toxicity, and environmental mobility. Herein, sulfur vacancy-rich Vs-Bi2S3@C nanocomposites were systematically synthesized via a one-step solvothermal vulcanization of CAU-17 precursor. Batch adsorption experiments demonstrated that the as-synthesized materials exhibited superior iodine adsorption capacity (1505.8 mg g-1 at 200 °C), fast equilibrium time (60 min), and high chemisorption ratio (91.7%), which might benefit from the nanowire structure and abundant sulfur vacancies of Bi2S3. Furthermore, Vs-Bi2S3@C composites exhibited excellent iodine capture performance in complex environments (high temperatures, high humidity and radiation exposure). Mechanistic investigations revealed that the I2 capture by fabricated materials primarily involved the chemical adsorption between Bi2S3 and I2 to form BiI3, and the interaction of I2 with electrons provided by sulfur vacancies to form polyiodide anions (I3-). The post-adsorbed iodine samples were successfully immobilized into commercial glass fractions in a stable form (BixOyI), exhibiting a normalized iodine leaching rate of 3.81 × 10-5 g m-2 d-1. Overall, our work offers a novel strategy for the design of adsorbent materials tailed for efficient capture and immobilization of volatile radioiodine.

Enhanced NO2 Sensitivity of Vertically Stacked van der Waals Heterostructure Gas Sensor and Its Remarkable Electric and Mechanical Tunability

Nanodevices based on van der Waals heterostructures have been predicted, and shown, to have unprecedented operational principles and functionalities that hold promise for highly sensitive and selective gas sensors with rapid response times and minimal power consumption. In this study, we fabricated gas sensors based on vertical MoS2/WS2 van der Waals heterostructures and investigated their gas sensing capabilities. Compared with individual MoS2 or WS2 gas sensors, the MoS2/WS2 van der Waals heterostructure gas sensors are shown to have enhanced sensitivity, faster response times, rapid recovery, and a notable selectivity, especially toward NO2. In combination with a theoretical model, we show that it is important to take into account created trapped states (flat bands) induced by the adsorption of gas molecules, which capture charges and alter the inherent built-in potential of van der Waals heterostructure gas sensors. Additionally, we note that the performance of these MoS2/WS2 heterostructure gas sensors could be further enhanced using electrical gating and mechanical strain. Our findings highlight the importance of understanding the effects of altered built-in potentials arising from gas molecule adsorption induced flat bands, thus offering a way to enhance the gas sensing performance of van der Waals heterostructure gas sensors.

ZnO-Au@ZIF-8 core-shell nanorod arrays for ppb-level NO2 detection

ZnO-Au@ZIF-8 core-shell heterostructures were prepared by ZIF-8 encapsulation of sacrificial ZnO-Au nanorods. Because of the catalytic activity of the Au nanoparticles and the sieving effects of the ZIF-8, the ZnO-Au@ZIF-8 heterostructures showed an outstanding response of 1.8 to 5 ppb NO2, and exhibited higher selectivity, stability, anti-humidity and fast response and recovery properties. The combination of the gas-selective catalytic activity of noble metals with the MOF filter used in this work can be easily extended to synthesize other types of MOS@MOF sensors, opening a new avenue for the detection of hazardous gases.

Biomimetic Wearable Sensors: Emerging Combination of Intelligence and Electronics

Owing to the advancement of interdisciplinary concepts, for example, wearable electronics, bioelectronics, and intelligent sensing, during the microelectronics industrial revolution, nowadays, extensively mature wearable sensing devices have become new favorites in the noninvasive human healthcare industry. The combination of wearable sensing devices with bionics is driving frontier developments in various fields, such as personalized medical monitoring and flexible electronics, due to the superior biocompatibilities and diverse sensing mechanisms. It is noticed that the integration of desired functions into wearable device materials can be realized by grafting biomimetic intelligence. Therefore, herein, the mechanism by which biomimetic materials satisfy and further enhance system functionality is reviewed. Next, wearable artificial sensory systems that integrate biomimetic sensing into portable sensing devices are introduced, which have received significant attention from the industry owing to their novel sensing approaches and portabilities. To address the limitations encountered by important signal and data units in biomimetic wearable sensing systems, two paths forward are identified and current challenges and opportunities are presented in this field. In summary, this review provides a further comprehensive understanding of the development of biomimetic wearable sensing devices from both breadth and depth perspectives, offering valuable guidance for future research and application expansion of these devices.

2D/2D Dy2O3 Nanosheet/MoO3 Nanoflake Heterostructures for Humidity-Independent and Sensitive Ammonia Detection

Chemiresistive ammonia gas (NH3) sensors have been playing a significant role in the fields of environmental protection, food safety monitoring, and air quality evaluation. Nevertheless, balancing the high sensitivity and humidity tolerance remains challenging. Herein, the two-dimensional (2D) heterostructures of molybdenum trioxide (MoO3) nanoflakes decorated with dysprosium oxide (Dy2O3) nanosheets (termed Dy2O3/MoO3) were synthesized via a facile probe-sonication method. With respect to pristine MoO3 counterparts, the optimal Dy2O3/MoO3 sensors possessed a 4.49-fold larger response at a lower temperature (30.52@328.2 °C vs 6.8@369.7 °C toward 10 ppm of NH3), shorter response/recovery times (11.6/2.9 s vs 26.9/43.4 s), 52.6-fold higher sensitivity (17.35/ppm vs 0.33/ppm), and a lower theoretical detection limit (1.02 vs 32.82 ppb). Besides the nice reversibility, wide detection range (0.45-100 ppm) and robust long-term stability, inspiringly, the Dy2O3/MoO3 sensors showed a nearly humidity-independent response. These impressive improvements in the NH3-sensing performance were attributed to numerous heterojunctions to strengthen the carrier concentration modulation and the compensation/protection effect of Dy2O3 to mitigate the humidity effect. Moreover, the Dy2O3/MoO3 sensors showed preliminary application potential in monitoring pork freshness. This work provides a universal methodology for constructing NH3 gas sensors with high sensitivity and good humidity resistance and probably extends the application scenarios of MoO3-based sensors in the Internet of Things in the future.

Four levels of in-sensor computing in bionic olfaction: from discrete components to multi-modal integrations

Sensing and computing are two important ways in which humans attempt to perceive and understand the analog world through digital devices. Analog-to-digital converters (ADCs) discretize analog signals while the data bus transmits digital data between the components of a computer. With the increase in sensor nodes and the application of deep neural networks, the energy and time consumption limit the increment of data throughput. In-sensor computing is a computing paradigm that integrates sensing, storage, and processing in one device without ADCs and data transfer. According to the integration degree, herein, we summarize four levels of in-sensor computing in the field of artificial olfactory. In the first level, we show that different functions are conducted by using discrete components. Next, the data conversion and transfer are exempt within the in-memory computing architecture with necessary data encoding. Subsequently, in-sensor computing is integrated into a single device. Finally, multi-modal in-sensor computing is proposed to improve the quality and reliability of the classification results. At the end of this minireview, we provide an outlook on the use of metal nanoparticle devices to achieve such in-sensor computing for bionic olfaction.

Synergy of S-vacancy and heterostructure in BiOCl/Bi2S3-x boosting room-temperature NO2 sensing

The special physicochemical properties of Bi₂S₃ nanomaterial endow it to be exceptional NO₂ sensing properties. However, sensors based on pure Bi₂S₃ cannot detect trace NO₂ at room temperature effectively due to the scanty active sites and poor charge transfer efficiency. Herein, vacancy defect and heterostructure engineering are rationally integrated to explore BiOCl/Bi₂S_3-x heterostructure with rich S vacancies to enhance NO₂ sensing performance. The optimized sensor based on S-vacancy-rich BiOCl/Bi₂S_3-x heterostructure exhibited a high response value (R_g/R_a = 29.1) to 1 ppm NO₂ at room temperature, which was about 17 times compared to the pristine Bi₂S₃. Meanwhile, the BiOCl/Bi₂S_3-x sensor also exhibited a short response time (36 s) towards 1 ppm NO₂ and a low theoretical detection limit (2 ppb). The superior response value of S-vacancy-rich BiOCl/Bi₂S_3-x heterostructures was ascribed to the improved electron migration at the heterointerface and the additional exposed active sites caused by the S vacancies in Bi₂S_3-x. Additionally, the sensors based on S-vacancy-rich BiOCl/Bi₂S_3-x heterostructures showed good long-term stability, outstanding selectivity, and good flexibility. This study offers an effective method for synergistically engineering defect and heterostructure to enhance gas sensing properties at room temperature.

Field Effect Transistor Gas Sensors Based on Mechanically Exfoliated Van der Waals Materials

The high surface-to-volume ratio and flatness of mechanically exfoliated van der Waals (vdW) layered materials make them an ideal platform to investigate the Langmuir absorption model. In this work, we fabricated field effect transistor gas sensors, based on a variety of mechanically exfoliated vdW materials, and investigated their electrical field-dependent gas sensing properties. The good agreement between the experimentally extracted intrinsic parameters, such as equilibrium constant and adsorption energy, and theoretically predicted values suggests validity of the Langmuir absorption model for vdW materials. Moreover, we show that the device sensing behavior depends crucially on the availability of carriers, and giant sensitivities and strong selectivity can be achieved at the sensitivity singularity. Finally, we demonstrate that such features provide a fingerprint for different gases to quickly detect and differentiate between low concentrations of mixed hazardous gases using sensor arrays.

Storage Stability of 6FDA-DMB Polyamic Acid Solution Detected by Gel Permeation Chromatography Coupled with Multiple Detectors

Polyamic acid (PAA) is the precursor of polyimide (PI), and its solution’s properties have a direct influence on the final performances of PI resins, films, or fibers. The viscosity loss of a PAA solution over time is notorious. A stability evaluation and revelation of the degradation mechanism of PAA in a solution based on variations of molecular parameters other than viscosity with storage time is necessary. In this study, a PAA solution was prepared through the polycondensation of 4,4′-(hexafluoroisopropene) diphthalic anhydride (6FDA) and 4,4′-diamino-2,2′-dimethylbiphenyl (DMB) in DMAc. The stability of a PAA solution stored at different temperatures (−18, −12, 4, and 25 °C) and different concentrations (12 wt% and 0.15 wt%) was systematically investigated by measuring the molecular parameters, including Mw, Mn, Mw/Mn, Rg, and [η], using gel permeation chromatography coupled with multiple detectors (GPC-RI-MALLS-VIS) in a mobile phase 0.02 M LiBr/0.20 M HAc/DMF. The stability of PAA in a concentrated solution decreased, as shown by the reduction ratio of Mw from 0%, 7.2%, and 34.7% to 83.8% and that of Mn from 0%, 4.7%, and 30.0% to 82.4% with an increase of temperature from −18, −12, and 4 to 25 °C, respectively, after storage for 139 days. The hydrolysis of PAA in a concentrated solution was accelerated at high temperatures. Notably, at 25 °C, the diluted solution was much less stable than the concentrated one and exhibited an almost linear degradation rate within 10 h. The Mw and Mn decreased rapidly by 52.8% and 48.7%, respectively, within 10 h. Such faster degradation was caused by a greater water ratio and less entanglement of chains in the diluted solution. The degradation of (6FDA-DMB) PAA in this study did not follow the chain length equilibration mechanism reported in literature, given that both Mw and Mn declined simultaneously during storage.

Two-dimensional black phosphorus/tin oxide heterojunctions for high-performance chemiresistive H2S sensing

Hydrogen sulfide (H₂S) emission from industrial fields and bacteria decomposing of sulfur-containing organic matter poses a significant impact on human health and atmospheric environment, thus necessitating the development of a H₂S sensor with high sensitivity and exclusive selectivity especially at a very low dose. Chemiresistive sensors based on traditional metal oxides were readily limited by the elevated operating temperature and severe cross-sensitivity. To overcome these obstacles, we prepared two dimensional (2D) tin oxide (SnO₂) nanosheets decorated with thin black phosphorus (BP) as the sensing layer of MEMS H₂S sensors. Compared with pure SnO₂ counterparts, BP-SnO₂ sensors demonstrated lower optimal working temperature (130 °C vs. 160 °C), higher response (8.1 vs. 4.6) and faster response/recovery speeds (39.8 s/47.4 s vs. 79 s/140 s) toward 5 ppm H₂S as well as larger sensitivity (1.3/ppm vs. 0.342/ppm). In addition, favorable repeatability, long-term stability, selectivity and humidity tolerance were exhibited. Thin BP not only served as an excellent conductivity platform within the composites, but enriched the adsorption sites by constructing p-n heterojunctions and introducing more oxygen vacancy, thus separately accelerating and strengthening the gas-solid interaction. This study showcased the application superiorities of BP nanosheets in the field of gas sensing, simultaneously providing a new strategy for trace H₂S sensing via the 2D heterojunctions.