Wearable Gas Sensor Based on Reticular Antimony-Doped SnO2/PANI Nanocomposite Realizing Intelligent Detection of Ammonia within a Wide Range of Humidity

Wearable, Breathable, and Wireless Gas Sensor Enables Highly Selective Exhaled Ammonia Detection and Real-Time Noninvasive Illness Diagnosis

Wearable gas sensors capable of real-time analysis of exhaled breath have been identified as ideal devices for noninvasive illness diagnosis. However, due to their inherent rigidity and brittleness, as well as high cross-sensitivity, conventional semiconductor gas sensors face significant challenges in achieving high flexibility, robustness, and selective exhaled breath analysis. Herein, we propose a wearable gas sensor by anchoring a SnS2 nanosheets/polyaniline (PANI) sensing layer in situ onto a permeable and flexible yttria-stabilized zirconia (YSZ) nanofiber substrate for the analysis of exhaled NH3. The cross-linked meshes of the YSZ network and the abundant voids between SnS2 nanosheets effectively release the stress concentration in YSZ/SnS2/PANI films, enabling the sensor to withstand severe folding/bending deformation. The organic PANI sheath endows the YSZ/SnS2/PANI-based gas sensor with enhanced toughness (0.66 kJ·m-3), stable electrical connection, and excellent robustness. The unique protonation/deprotonation sensing mechanism, coupled with the heterojunction effect of the sensing layer, ensures outstanding selectivity (sensor immunity coefficient ≈ 69%) and a high response to NH3. To support wearable applications, the sensing signals from the wearable sensor are transmitted wirelessly via Bluetooth and displayed on a smartphone. This work greatly advances the application of a wearable semiconductor sensor in personal disease diagnosis.

Recent Advances in Functionalizing Metal Oxide Semiconductors for Highly Sensitive Gas Sensors

Metal oxide semiconductors (MOSs) have emerged as pivotal materials for gas sensing technologies due to their inherent advantages, including cost-effectiveness, simplicity in synthesis, and easy fabrication of sensing nanodevices. These characteristics have made MOSs widely applicable in industrial, environmental, and biological monitoring. While MOSs offer intrinsic gas-sensing properties, their limited active site density and function diversity restrict sensitivity and selectivity, especially in complex gaseous environments. To overcome these limitations, extensive research efforts have been devoted to functionalizing MOSs through strategies such as heterojunction construction, noble metal nanoparticle loading (e.g., Au, Pt, Ag, Pd), and heteroatom doping (e.g., Si, Cr). Furthermore, composite materials have emerged as an effective approach to enhance MOSs-based gas sensors by integrating carbon-based materials or polymers to leverage synergistic interactions. These modifications expand the applicability of MOSs sensors for detecting volatile organic compounds, toxic gases, and flammable gases. This review systematically examines the synthesis strategies and performance enhancements achieved through MOSs functionalization and composite material integration, emphasizing structure-property relationships, interfacial charge transfer dynamics, and adsorption mechanisms. Finally, the challenges and future directions for the rational design of next-generation MOSs-based gas sensors are outlined, providing critical insights for advancing intelligent gas sensing technologies.

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.

Organic Indium Halides with Near-Unity Photoluminescence Quantum Yields for Highly Efficient Luminescent Inks and White Light Emitting Diodes

Zero-dimensional (0D) organic indium halides have been emerged as promising broadband light emitters with wide application prospects, but most of the present halides suffer from low photoluminescence quantum yield (PLQY), and a high-power excitation light source is needed to obtain desirable performance. In this work, we elaborately select appropriate organic cations as crystal structural engineering and obtained a series of highly efficient 0D indium bromides. Under UV light excitation, these 0D indium halides display broadband yellow light emissions (550-600 nm) with near-unity PLQYs, which represents one of the highest values in all the previously reported indium halides. Benefiting from successful nanoscale engineering, highly luminescent inks based on these 0D indium halides are facilely prepared by dispersing nanocrystals into various organic solvents. The luminescent ink can be utilized to print various anticounterfeiting patterns, which displays photoreversible switching with visible/invisible transformation under the alternating irradiation of UV and visible light. Furthermore, white light emitting diodes can be fabricated with high color rendering index above 90 by using these 0D halides as down-conversion phosphors. This work not only promotes the development of indium halides but also significantly broadens the application in solid-state illumination and anticounterfeiting, etc.

Construction of trace nitric oxide sensors at low temperature based on bulk embedded BiVO4 in SnO2 nanofibers with nano-heterointerfaces

Constructing heterostructures is an effective way to improve the carrier mobility for metal oxide sensing material, since heterojunctions are usually built only on the surface of the material, the carrier transport efficiency inside the material still needs to be improved. In this paper, BiVO4 nanocrystals (BVO NCs) with an average size of 1 nm generated by pulsed laser irradiation were embedded in situ at the particle boundaries (PBs) of SnO2 nanofibers to form an effective n-n heterojunctions inside the material. After embedding the BVO NCs in the SnO2 samples, the response value for 10 ppm NO was improved to 48.91, which was 2.5 times higher than that of pure SnO2 at near room temperature (50 °C). Meanwhile, the detection limit was lowered to 50 ppb with excellent long term stability. Detailed analysis and theoretical calculations demonstrated that the formation of abundant n-n heterojunctions not only promotes the electron-hole separation and the carrier mobility, but also reduces the conductivity and adsorption energy of the material, which significantly improves its sensing performance. This work demonstrates a new approach to modulate the gas-sensing performance of metal oxide semiconductors by generating heterostructure inside the bulk of the material.

Ppb-Level Ammonia Sensor for Exhaled Breath Diagnosis Based on UV-DOAS Combined with Spectral Reconstruction Fitting Neural Network

Ammonia (NH3) in exhaled breath (EB) has been a biomarker for kidney function, and accurate measurement of NH3 is essential for early screening of kidney disease. In this work, we report an optical sensor that combines ultraviolet differential optical absorption spectroscopy (UV-DOAS) and spectral reconstruction fitting neural network (SRFNN) for detecting NH3 in EB. UV-DOAS is introduced to eliminate interference from slow change absorption in the EB spectrum while spectral reconstruction fitting is proposed for the first time to map the original spectra onto the sine function spectra by the principle of least absolute deviations. The sine function spectra are then fitted by the least-squares method to eliminate noise signals and the interference of exhaled nitric oxide. Finally, the neural network is built to enable the detection of NH3 in EB at parts per billion (ppb) level. The laboratory results show that the detection range is 9.50-12425.82 ppb, the mean absolute percentage error (MAPE) is 0.83%, and the detection accuracy is 0.42%. Experimental results prove that the sensor can detect breath NH3 and identify EB in simulated patients and healthy people. Our sensor will serve as a new and effective system for detecting breath NH3 with high accuracy and stability in the medical field.

Ultra-Flexible, Breathable, and Robust PAN/MWCNTs/PANI Nanofiber Networks for High-Performance Wearable Gas Sensor Application

Wearable gas sensors have drawn great attention for potential applications in health monitoring, minienvironment detection, and advanced soft electronic noses. However, it still remains a great challenge to simultaneously achieve excellent flexibility, high sensitivity, robustness, and gas permeability, because of the inherent limitation of widely used traditional organic flexible substrates. Herein, an electrospinning polyacrylonitrile (PAN) nanofiber network was designed as a flexible substrate, on which an ultraflexible wearable gas sensor was prepared with in situ assembled polyaniline (PANI) and multiwalled carbon nanotubes (MWCNTs) as a sensitive layer. The unique nanofiber network and strong binding force between substrate and sensing materials endow the wearable gas sensor with excellent robustness, flexibility, and gas permeability. The wearable sensor can maintain stable NH3 sensing performance while sustaining extreme bending and stretching (50% of strain). The Young's modulus of wearable PAN/MWCNTs/PANI sensor is as low as 18.9 MPa, which is several orders of magnitude smaller than those of reported flexible sensors. The water vapor transmission rate of the sensor is 0.38 g/(cm2 24 h), which enables the wearing comfort of the sensor. Most importantly, due to the effective exposure of sensing sites as well as the heterostructure effect between MWCNTs and PANI, the sensor shows high sensitivity to NH3 at room temperature, and the theoretical limit of detection is as low as 300 ppb. This work provides a new avenue for the realization of reliable and high-performance wearable gas sensors.