Pt/MoS2/Polyaniline Nanocomposite as a Highly Effective Room Temperature Flexible Gas Sensor for Ammonia Detection

Noninvasive Diagnosis of Early-Stage Chronic Kidney Disease and Monitoring of the Hemodialysis Process in Clinical Practice via Exhaled Breath Analysis Using an Ultrasensitive Flexible NH3 Sensor Assisted by Pattern Recognition

To achieve the early diagnosis of chronic kidney disease (CKD), noninvasive hemodialysis monitoring, and accurate determination of dialysis duration and adequacy, a noninvasive, point-of-care, user-friendly device should be developed. Here, a flexible, room temperature NH3 gas sensor sensitive to the key breath biomarkers of CKD─NH3 and creatinine─was fabricated. The sensor had detection limits of 100 ppb for NH3 and 1 ppm for creatinine. Clinically, a total of 96 exhaled breath samples, half from 39 CKD patients and the other half from 48 healthy controls were collected and analyzed. With the assistance of a pattern recognition algorithm , the early diagnosis of CKD was achieved by the sensor, with PCA being used due to sensor's cross-sensitivity to CKD biomarkers. Diagnostic models distinguishing CKD versus non-CKD and early-stage CKD versus advanced-stage CKD were constructed using the SVM algorithm, achieving an overall accuracy of 0.93 and 0.94, with area under the curve (AUC) values of 0.97 and 0.99 for all subjects in receiver operating characteristic (ROC) analysis, respectively. The hemodialysis processes of patients were monitored in real-time, with the sensor response values exhibiting ideal exponential decay over time. The sensor response values showed a strong positive correlation with serum creatinine levels (r = 0.85) and a moderate positive correlation with blood urea nitrogen levels (r = 0.62), both of which are key clinical diagnostic indicators for CKD. These are good results, as 54% of CKD samples are from early-stage CKD patients. These results suggest that the sensor could serve as a noninvasive alternative to traditional blood tests for renal function evaluation and CKD diagnosis. Overall, this sensor demonstrates great potential in clinical practice for early diagnosis of CKD, monitoring the daily health status of CKD patients, optimizing the dialysis schedule, and monitoring the dialysis process in real-time.

Ultrasensitive ammonia sensor with excellent humidity resistance based on PANI/SnS2 heterojunction

The analysis of human exhaled gas is crucial for early and noninvasive diagnosis. However, the complex composition and high-humidity of exhaled gas pose significant challenges to the application of gas sensors. This research focuses on the development of a chemiresistive ammonia sensor based on the polyaniline/tin disulfide (PANI/SnS2) heterojunction, which is fabricated by hydrothermal and in-situ polymerization techniques. The sensor demonstrates significantly enhanced gas sensing capabilities manifested by increased responsiveness, improved selectivity, and stability for detecting 0.5-100 ppm ammonia at ambient temperature. Notably, the sensor exhibits a marked enhancement in response at high humidity levels. When exposed to 30 ppm of ammonia, the sensor's response value increases by 167 % at a relative humidity (RH) of 80 %, compared to 128 % at 50 % RH. This significant improvement can be attributed to the unique interaction between water molecules and the sensor material, which enhances the overall charge transfer processes at the PANI/SnS2 interface. Furthermore, in-situ techniques as well as theoretical calculations are utilized to gain insight into the sensitization mechanism. The proposed PANI/SnS2 heterojunction sensor shows great promise for applications in high-humidity environment at ambient temperature.

Next-Generation Chemiresistive Wearable Breath Sensors for Non-Invasive Healthcare Monitoring: Advances in Composite and Hybrid Materials

Recently wearable breath sensors have received significant attention in personalized healthcare systems by offering new methods for remote, non-invasive, and continuous monitoring of various health indicators from breath samples without disrupting daily routines. The rising demand for rapid, personalized diagnostics has sparked concerns over electronic waste from short-lived silicon-based devices. To address this issue, the development of flexible and wearable sensors for breath sensing applications is a promising approach. Research highlights the development of different flexible, wearable sensors operating with different operating principles, such as chemiresistive sensors to detect specific target analytes due to their simple design, high sensitivity, selectivity, and reliability. Further, focusing on the non-invasive detection of biomarkers through exhaled breath, chemiresistive wearable sensors offer a comprehensive and environmentally friendly solution. This article presents a comprehensive discussion of the recent advancement in chemiresistive wearable breath sensors for the non-invasive detection of breath biomarkers. The article further emphasizes the intricate development and functioning of the sensor, including the selection criteria for both the flexible substrate and advanced functional materials, including their sensing mechanisms. The review then explores the potential applications of wearable gas sensing systems with specific disease detection, with modern challenges associated with non-invasive breath sensors.

Nanomaterial Innovations and Machine Learning in Gas Sensing Technologies for Real-Time Health Diagnostics

Breath sensors represent a frontier in noninvasive diagnostics, leveraging the detection of volatile organic compounds (VOCs) in exhaled breath for real-time health monitoring. This review highlights recent advancements in breath-sensing technologies, with a focus on the innovative materials driving their enhanced sensitivity and selectivity. Polymers, carbon-based materials like graphene and carbon nanotubes, and metal oxides such as ZnO and SnO2 have demonstrated significant potential in detecting biomarkers related to diseases including diabetes, liver/kidney dysfunction, asthma, and gut health. The structural and operational principles of these materials are examined, revealing how their unique properties contribute to the detection of key respiratory gases like acetone, ammonia (NH3), hydrogen sulfide, and nitric oxide. The complexity of breath samples is addressed through the integration of machine learning (ML) algorithms, including convolutional neural networks (CNNs) and support vector machines (SVMs), which optimize data interpretation and diagnostic accuracy. In addition to sensing VOCs, these devices are capable of monitoring parameters such as airflow, temperature, and humidity, essential for comprehensive breath analysis. This review also explores the expanding role of artificial intelligence (AI) in transforming wearable breath sensors into sophisticated tools for personalized health diagnostics, enabling real-time disease detection and monitoring. Together, advances in sensor materials and ML-based analytics present a promising platform for the future of individualized, noninvasive healthcare.

Insights into Selective Sensitivity of In2O3-CuO Heterojunction Nanocrystals to CH4 over CO and H2: Experiments and First-Principles Calculations

Metal oxide semiconductor gas sensors have demonstrated exceptional potential in gas detection due to their high sensitivity, rapid response time, and impressive selectivity for identifying various sorts of gases. However, selectively distinguishing CH4 from those of CO and H2 remains a significant challenge. This difficulty primarily stems from the weakly reducing nature of CH4, which results in a low adsorption response and makes it prone to interference from stronger reducing gases in the surroundings. Herein, we synthesized In2O3-xCuO nanocomposites using a hydrothermal method to explore their gas sensing properties toward CH4, CO, and H2. Characterization tests confirmed the successful preparation of In2O3-xCuO nanocomposites with different In:Cu molar ratios and the formation of a p-n heterojunction. The gas sensing test results indicated that the In2O3-2.1CuO nanocomposites calcined at 500 °C and measured at 350 °C displayed a p-type response for CH4 and an n-type response for CO and H2, allowing for accurate differentiation of CH4 from CO and H2. Moreover, the In2O3-2.1CuO sensor also showed excellent stability and reproducibility across all three gases. First-principles calculations revealed distinct changes in the electronic structure of the In2O3-CuO heterojunction upon adsorption of CH4, CO, and H2, a finding that aligns with empirical evidence. The gas selectivity mechanism was effectively explained by variations in the energy band gap, driven by electrical behavior during the adsorption process. This work suggests a promising approach for developing selective gas sensors capable of detecting weakly reducing gases.

Porous and Homogeneous Nanoheterojunction-Accumulating PdO@ZnO Structure for Exhaled Breath Ammonia Sensing

The functional gas sensor device plays a pivotal role in intelligent medical treatment, among which metal oxide semiconductors are widely studied because of their inexpensiveness and ease of fabrication. However, the metal oxide sensors present a significant challenge in detecting NH3 at ppm levels within complex exhaled gases. Herein, the ZnO/PdO-x series were prepared by in situ loading palladium particles and calcining using nano-ZIF-8 as a precursor, which not only provided more transport path for ammonia adsorption but also achieved homogeneous nanoheterojunction accumulation structure. The tailor-made ZnO/PdO-2 sensor exhibits the optimum gas sensitivity, with a response value of 5.56 for 100 ppm of NH3 at 160 °C and a lower detection limit of 0.75 ppm. Particularly, it has a clear quantitative response to the actual exhaled gas of liver and kidney patients. By elucidating the intrinsic link between the in situ loading of MOF templates and the sensing mechanism, it is expected to broaden the rational design of metal-oxide sensors and thus provide an effective method for clinical detection.

Ultrahigh humidity-resistance ppb-level formaldehyde sensing at room temperature induced by fluorinated dipole based "umbrella" and "bridge"

Formaldehyde (HCHO) is a major indoor pollutant that is extremely harmful to human health even at ppb-level. Meanwhile, ppb-level HCHO is also a potential disease marker in the exhalation of patients with respiratory diseases. Higher humidity resistance and lower practical limit of detection (pLOD) both have to be pursued for practical HCHO sensors. In this work, by assembling indium oxide (In2O3) and fluorinated dipole modified reduced graphene oxide (rGO), we prepared a high-performance room temperature HCHO sensor (In2O3 @ATQ-rGO). Excellent sensing properties toward HCHO under visible illumination have been achieved, including ultra-low pLOD of 3 ppb and high humidity-resistance. By control experiments and density functional theory calculation, it is indicated that the introduced fluorinated dipoles act as not only an "umbrella" to improve the humidity resistance of the composite, but also a "bridge" to accelerate the electron transport, improving the sensitivity of the material. The significant practicality and reliability of the obtained sensors were verified by in-situ simulation experiments using a 3 m3 test chamber with a humidity control system and by detection of the simulated lung disease patient's exhalation. This work provides an effective strategy of simultaneously achieving high humidity-resistance and low pLOD of room temperature formaldehyde sensing materials.

Wide-range and high-accuracy wireless sensor with self-humidity compensation for real-time ammonia monitoring

Real-time and accurate biomarker detection is highly desired in point-of-care diagnosis, food freshness monitoring, and hazardous leakage warning. However, achieving such an objective with existing technologies is still challenging. Herein, we demonstrate a wireless inductor-capacitor (LC) chemical sensor based on platinum-doped partially deprotonated-polypyrrole (Pt-PPy+ and PPy0) for real-time and accurate ammonia (NH3) detection. With the chemically wide-range tunability of PPy in conductivity to modulate the impedance, the LC sensor exhibits an up-to-180% improvement in return loss (S11). The Pt-PPy+ and PPy0 shows the p-type semiconductor nature with greatly-manifested adsorption-charge transfer dynamics toward NH3, leading to an unprecedented NH3 sensing range. The S11 and frequency of the Pt-PPy+ and PPy0-based sensor exhibit discriminative response behaviors to humidity and NH3, enabling the without-external-calibration compensation and accurate NH3 detection. A portable system combining the proposed wireless chemical sensor and a handheld instrument is validated, which aids in rationalizing strategies for individuals toward various scenarios.

Enhanced Triethylamine Detection at Room Temperature Using a Layered MoS2 Nanosheet-Coated PPy Nanorod: A Comprehensive Study

The rapid and reliable detection of triethylamine (TEA), a toxic, explosive, volatile organic compound at room temperature, is highly significant for food safety, environmental, and human health monitoring. This manuscript reports a layered molybdenum disulfide (MoS2) nanosheet-coated polypyrrole (PPy) nanorod-based heterostructure sensor (MsPy) which offers superior sensing properties toward TEA at room temperature (25 °C). Herein, different MsPy nanocomposites were synthesized, followed by a controlled sulfidation reaction through dissolution, diffusion, and regrowth mechanisms. Optimizing the ratio of the precursor of molybdenum trioxide (MoO3/PPy) is crucial for achieving effective deposition of a layered MoS2 nanosheet on the PPy surface. The as-prepared MoS2 nanosheet-coated PPy sensor (MsPy_40) enables one to selectively detect trace TEA vapor at 25 °C with a detection lower limit of 0.5 ppm. The MsPy_40 sensor exhibits 17 times higher response than the pristine MoS2 nanosheet to 50 ppm TEA, with rapid response (∼3.9 s) and recovery (∼19.6 s), along with better stability, good selectivity, and remarkable repeatability. The significantly enhanced sensing performance is attributed to the unique surface morphology of the layered MoS2 nanosheet-coated PPy nanorod and the formation of a p-n heterojunction between PPy and MoS2.

Resistive gas sensors for the detection of NH3gas based on 2D WS2, WSe2, MoS2, and MoSe2: a review

Transition metal dichalcogenides (TMDs) with a two-dimensional (2D) structure and semiconducting features are highly favorable for the production of NH3gas sensors. Among the TMD family, WS2, WSe2, MoS2, and MoSe2exhibit high conductivity and a high surface area, along with high availability, reasons for which they are favored in gas-sensing studies. In this review, we have discussed the structure, synthesis, and NH3sensing characteristics of pristine, decorated, doped, and composite-based WS2, WSe2, MoS2, and MoSe2gas sensors. Both experimental and theoretical studies are considered. Furthermore, both room temperature and higher temperature gas sensors are discussed. We also emphasized the gas-sensing mechanism. Thus, this review provides a reference for researchers working in the field of 2D TMD gas sensors.

Selective Detection of NH3 Gas by Ti3C2Tx Sensors with the PVDF-ZIF-67 Overlayer at Room Temperature

In the realm of NH3 gas-sensing applications, the electrically conductive nature of Ti3C2Tx MXene, adorned with surface terminations such as -O and -OH groups, renders it a compelling material. However, the inherent challenges of atmospheric instability and selectivity in the presence of gas mixtures have prompted the exploration of innovative solutions. This work introduces a strategic solution through the deposition of a mixed-matrix membrane (MMM) composed of poly(vinylidene fluoride) (PVDF) as the matrix and zeolitic imidazolate framework-67 (ZIF-67) as the filler. This composite membrane acts as a selective filter, permitting the passage of a specific gas, namely NH3. Leveraging the hydrophobic and chemically inert nature of PVDF, the MMM enhances the atmospheric stability of Ti3C2Tx by impeding water molecules from interacting with the MXene. Furthermore, ZIF-67 is selective to NH3 gas via acid-base interactions within the zeolite group and selective pore size. The Ti3C2Tx sensor embedded in the MMM filter exhibits a modest 1.3% change in the sensing response to 25 ppm of NH3 gas compared to the response without the filter. This result underscores the filter's effectiveness in conferring selectivity and diffusivity, particularly at 35% relative humidity (RH) and 25 °C. Crucially, the hydrophobic attributes of PVDF impart heightened stability to the Ti3C2Tx sensor even amidst varying RH conditions. These results not only demonstrate effective NH3 detection but also highlight the sensor's adaptability to diverse environmental conditions, offering promising prospects for practical applications.

Edge sulfur vacancies riched MoS2 nanosheets assist PEDOT:PSS flexible film ammonia sensing enhancement for wireless greenhouse vegetables monitoring

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a promising NH3 sensing material owing to its super high electrical conductivity, excellent environmental stability, and reversible doping/dedoping nature. However, the low sensitivity and sluggish recovery rate limit its further application in gas sensors. Herein, exfoliated layered MoS2 nanosheets with large-specific surface area and abundant edge sulfur (S) vacancies are utilized to assist PEDOT:PSS and achieve ideal improvement in NH3 sensing performance at room temperature (RT), including high response values, fast response/recovery ability, and excellent sensing stability in complex environment. MoS2 nanosheets are combined with PEDOT:PSS to construct p-n heterojunction, the S vacancies can improve carrier transfer rate and serve as conductive bridge, effective active sites for NH3 adsorption, this series of performance improvement strategies is the significance of this work. Meanwhile, the density-functional theory (DFT), current-voltage (I-V), and in-situ FITR are firstly employed to discuss the sensing mechanisms in detail. Furthermore, integrating MoS2/PEDOT:PSS flexible sensor into a designed printed circuit board to intelligent, visual, and wireless real-time monitoring the NH3 resistance information in a simulated greenhouse vegetables equipment through the smartphone APP has also been successfully implemented.

Zinc Oxide-Loaded Cellulose-Based Carbon Gas Sensor for Selective Detection of Ammonia

Cellulose-based carbon (CBC) is widely known for its porous structure and high specific surface area and is liable to adsorb gas molecules and macromolecular pollutants. However, the application of CBC in gas sensing has been little studied. In this paper, a ZnO/CBC heterojunction was formed by means of simple co-precipitation and high-temperature carbonization. As a new ammonia sensor, the prepared ZnO/CBC sensor can detect ammonia that the previous pure ZnO ammonia sensor cannot at room temperature. It has a great gas sensing response, stability, and selectivity to an ammonia concentration of 200 ppm. This study provides a new idea for the design and synthesis of biomass carbon-metal oxide composites.

Capping Ligand Engineering Enables Stable CsPbBr3 Perovskite Quantum Dots toward White-Light-Emitting Diodes

All-inorganic perovskite quantum dots (PeQDs) have sparked extensive research focus on white-light-emitting diodes (WLEDs), but stability and photoluminescence efficiency issues are still remain obstacles impeding their practical application. Here, we reported a facile one-step method to synthesize CsPbBr₃ PeQDs at room temperature using branched didodecyldimethylammonium fluoride (DDAF) and short-chain-length octanoic acid as capping ligands. The obtained CsPbBr₃ PeQDs have a near-unity photoluminescence quantum yield of 97% due to the effective passivation of DDAF. More importantly, they exhibit much improved stability against air, heat, and polar solvents, maintaining >70% of initial PL intensity. Making use of these excellent optoelectronic properties, WLEDs based on CsPbBr₃ PeQDs, CsPbBr_1.2I_1.8 PeQDs, and blue LEDs were fabricated, which show a color gamut of 122.7% of the National Television System Committee standard, a luminous efficacy of 17.1 lm/W, with a color temperature of 5890 K, and CIE coordinates of (0.32, 0.35). These results indicate that the CsPbBr₃ PeQDs have great practical potential in wide-color-gamut displays.