A Versatile Method to Enhance the Operational Current of Air-Stable Organic Gas Sensor for Monitoring of Breath Ammonia in Hemodialysis Patients

Poly(3-hexylthiophene) as a versatile semiconducting polymer for cutting-edge bioelectronics

Semiconducting polymers (SPs), widely used in organic optoelectronics, are gaining interest in bioelectronics owing to their intrinsic optical properties, conductivity, biocompatibility, flexibility, and chemical tunability. Among them, poly(3-hexylthiophene) (P3HT) has attracted great attention as a versatile SP, being both optically active and conductive, for the fabrication of smart materials (e.g., films and nanoparticles), allowing the modulation of their performance and final biomedical applications. This review article provides an overview of the design of different kinds of P3HT-based materials, from chemical properties to structural engineering, to be used as key opto-electronic components in the development of opto-transducers for the modulation of cell fate, as well as biosensors such as organic electrochemical transistors (OECTs) and organic field effect transistors (OEFTs). Finally, their foremost applications in the biomedical field ranging from tissue engineering to biosensing will be discussed, including the future perspectives of P3HT derivatives towards cutting-edge applications for bioelectronics, in which optoceutics plays a key role.

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.

Wearable face mask-attached disposable printed sensor arrays for point-of-need monitoring of alkaline gases in breath

Blood sampling, despite its historical significance in clinical diagnostics, poses challenges, such as invasiveness, infection risks, and limited temporal fidelity for continuous monitoring. In contrast, exhaled breath offers a noninvasive, pain-free, and continuous sampling method, carrying biochemical information through volatile compounds like ammonia (NH3). NH3 in exhaled breath, influenced by kidney function, emerges as a promising biomarker for renal health assessment, particularly in resource-limited settings lacking extensive healthcare infrastructure. Current analytical methods for breath NH3, though effective, often face practical limitations. In this work, we introduce a low-cost, internet-connected, paper-based wearable device for measuring exhaled NH3, designed for early detection of kidney dysfunction at the point of need. The device, which attaches to disposable face masks, utilizes an array of disposable paper-based sensors to detect NH3 with the readout being changes in electrical impedance that correlate with the concentration of NH3. The sensor array is housed in a biodegradable plastic enclosure to mitigate high relative humidity issues in breath analysis. We validated our technology using a laboratory setup and human subjects who consumed ammonium chloride-containing candy to simulate elevated breath NH3. Our wearable sensor offers a promising solution for rapid, point-of-need kidney dysfunction screening, particularly valuable in resource-limited settings. This approach has potential applications beyond kidney health monitoring, including chemical industry safety and environmental sensing, paving the way for accessible, continuous health monitoring.

Humidity activated ultra-selective room temperature gas sensor based on W doped MoS2/RGO composites for trace level ammonia detection

The lack of highly efficient, cost effective and stable ammonia gas sensors functionable at room temperature even in extreme humid environments poses significant challenge for the future generation gas sensors. The prime factors that impede the development of such next generation gas sensors are the strong interference of humidity and sluggish selectivity. Herein, we fabricated tungsten doped molybdenum disulphide/reduced graphene oxide composite by an in-situ hydrothermal method to exploit the adsorption, dissolution (solubility), ionization and transmission process of ammonia and thereby to effectuate its trace level detection even in indispensable humid environments. The protype based on 5 at.% Tungsten doped MoS2/RGO (W5) gas sensor exhibited 3.8-fold increment in its response to 50 ppm of ammonia when the relative humidity varied from 20 % to 70 % with ultra-high selectivity at room temperature. The as prepared gas sensor revealed a practical detection limit down to 1 ppm with a substantial response and rapid recovery time. Furthermore, W5 gas sensor exhibited a 42-fold increment in response to 50 ppm of ammonia relative to its pristine (MoS2/RGO) MG composite with a RH of 70 %. The proton hopping mechanism accountable for such an enormous enhancement in ammonia sensing and its potential for breath sensor are briefly annotated.

Ultrathin Serpentine Insulation Layer Architecture for Ultralow Power Gas Sensor

Toxic gases have surreptitiously influenced the health and environment of contemporary society with their odorless/colorless characteristics. As a result, a pressing need for reliable and portable gas-sensing devices has continuously increased. However, with their negligence to efficiently microstructure their bulky supportive layer on which the sensing and heating materials are located, previous semiconductor metal-oxide gas sensors have been unable to fully enhance their power efficiency, a critical factor in power-stringent portable devices. Herein, an ultrathin insulation layer with a unique serpentine architecture is proposed for the development of a power-efficient gas sensor, consuming only 2.3 mW with an operating temperature of 300 °C (≈6% of the leading commercial product). Utilizing a mechanically robust serpentine design, this work presents a fully suspended standalone device with a supportive layer thickness of only ≈50 nm. The developed gas sensor shows excellent mechanical durability, operating over 10 000 on/off cycles and ≈2 years of life expectancy under continuous operation. The gas sensor detected carbon monoxide concentrations from 30 to 1 ppm with an average response time of ≈15 s and distinguishable sensitivity to 1 ppm (ΔR/R0 = 5%). The mass-producible fabrication and heating efficiency presented here provide an exemplary platform for diverse power-efficient-related devices.

Influence of dopant concentration on the ammonia sensing performance of citric acid-doped polyvinyl acetate nanofibers

The chemical modification of polymer nanofiber-based ammonia sensors by introducing dopants into the active layers has been proven as one of the low-cost routes to enhance their sensing performance. Herein, we investigate the influence of different citric acid (CA) concentrations on electrospun polyvinyl acetate (PVAc) nanofibers coated on quartz crystal microbalance (QCM) transducers as gravimetric ammonia sensors. The developed CA-doped PVAc nanofiber sensors are tested against various concentrations of ammonia vapors, in which their key sensing performance parameters (i.e., sensitivity, limit of detection (LOD), limit of quantification (LOQ), and repeatability) are studied in detail. The sensitivity and LOD values of 1.34 Hz ppm^-1 and 1 ppm, respectively, can be obtained during ammonia exposure assessment. Adding CA dopants with a higher concentration not only increases the sensor sensitivity linearly, but also prolongs both response and recovery times. This finding allows us to better understand the dopant concentration effect, which subsequently can result in an appropriate strategy for manufacturing high-performance portable nanofiber-based sensing devices.

Study on Ammonia Content and Distribution in the Microenvironment Based on Covalent Organic Framework Nanochannels

A crack-free micrometer-sized compact structure of 1,3,5-tris(4-aminophenyl)benzene-terephthaldehyde-covalent organic frameworks (TAPB-PDA-COFs) was constructed in situ at the tip of a theta micropipette (TMP). The COF-covered theta micropipette (CTP) then created a stable liquid-gas interface inside COF nanochannels, which was utilized to electrochemically analyze the content and distribution of ammonia gas in the microenvironments. The TMP-based electrochemical ammonia sensor (TEAS) shows a high sensing response, with current increasing linearly from 0 to 50,000 ppm ammonia, owing to the absorption of ammonia gas in the solvent meniscus that connects both barrels of the TEAS. The TEAS also exhibits a short response and recovery time of 5 ± 2 s and 6 ± 2 s, respectively. This response of the ammonia sensor is remarkably stable and repeatable, with a relative standard deviation of 6% for 500 ppm ammonia gas dispensing with humidity control. Due to its fast, reproducible, and stable response to ammonia gas, the TEAS was also utilized as a scanning electrochemical microscopy (SECM) probe for imaging the distribution of ammonia gas in a microspace. This study unlocks new possibilities for using a TMP in designing microscale probes for gas sensing and imaging.

Self-Powered Respiration Monitoring Enabled By a Triboelectric Nanogenerator

In mammals, physiological respiration involves respiratory cycles of inhaled and exhaled breaths, which has traditionally been an underutilized resource potentially encompassing a wealth of physiologically relevant information as well as clues to potential diseases. Recently, triboelectric nanogenerators (TENGs) have been widely adopted for self-powered respiration monitoring owing to their compelling features, such as decent biocompatibility, wearing comfort, low-cost, and high sensitivity to respiration activities in the aspect of low frequency and slight amplitude body motions. Physiological respiration behaviors and exhaled chemical regents can be precisely and continuously monitored by TENG-based respiration sensors for personalized health care. This article presents an overview of TENG enabled self-powered respiration monitoring, with a focus on the working principle, sensing materials, functional structures, and related applications in both physical respiration motion detection and chemical breath analysis. Concepts and approaches for acquisition of physical information associated with respiratory rate and depth are covered in the first part. Then the sensing mechanism, theoretical modeling, and applications related to detection of chemicals released from breathing gases are systemically summarized. Finally, the opportunities and challenges of triboelectric effect enabled self-powered respiration monitoring are comprehensively discussed and criticized.

Solution-Processed Chloroaluminum Phthalocyanine (ClAlPc) Ammonia Gas Sensor with Vertical Organic Porous Diodes

In this research work, the gas sensing properties of halogenated chloroaluminum phthalocyanine (ClAlPc) thin films were studied at room temperature. We fabricated an air-stable ClAlPc gas sensor based on a vertical organic diode (VOD) with a porous top electrode by the solution process method. The surface morphology of the solution-processed ClAlPc thin film was examined by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The proposed ClAlPc-based VOD sensor can detect ammonia (NH3) gas at the ppb level (100~1000 ppb) at room temperature. Additionally, the ClAlPc sensor was highly selective towards NH3 gas compared to other interfering gases (NO2, ACE, NO, H2S, and CO). In addition, the device lifetime was tested by storing the device at ambient conditions. The effect of relative humidity (RH) on the ClAlPc NH3 gas sensor was also explored. The aim of this study is to extend these findings on halogenated phthalocyanine-based materials to practical electronic nose applications in the future.

Noninvasive Detection of Ammonia in the Breath of Hemodialysis Patients Using a Highly Sensitive Ammonia Sensor Based on a Polypyrrole/Sulfonated Graphene Nanocomposite

In this work, we fabricated fast-responsive and highly sensitive chemiresistive sensors based on nanocomposites of polypyrrole and graphitic materials such as graphene oxide (GO), reduced graphene oxide (RGO), and sulfonated graphene (SRGO) by an in situ chemical oxidative polymerization method. The synthesized nanocomposites were characterized using field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD). The effects of the operating temperature of different nanocomposites were investigated at four temperatures (28, 40, 50, and 60 °C), and the results were compared with that of the polypyrrole-based sensor. The experimental results for sensors indicate that the proposed PPy/SRGO sensor could be an appropriate choice for NH₃ detection at 28 °C in the range of 0.50 parts per billion (ppb) to 12 parts per million (ppm). The PPy/SRGO nanocomposite gas sensor exhibited fast responsivity, good repeatability, and high chemical selectivity to low-concentration ammonia against humidity, methanol, ethanol, acetone, formaldehyde, dibutylamine, dimethylamine, methylamine, carbon monoxide, and nitrogen oxide at 28 °C. We utilized the PPy/SRGO sensor for studying the variation of the ammonia concentration in hemodialysis (HD) patients' breath before and after dialysis and correlated it with the blood urea nitrogen (BUN) levels. The results of the PPy/SRGO sensor indicated that the breath ammonia concentration significantly decreased after dialysis in agreement with BUN. The results demonstrate the potential application of the PPy/SRGO sensor for noninvasive detection of ammonia in breath and make this type of sensor a promising tool for the diagnosis of renal and liver diseases.

Recent Advances in Ammonia Gas Sensors Based on Carbon Nanomaterials

This review paper is devoted to an extended analysis of ammonia gas sensors based on carbon nanomaterials. It provides a detailed comparison of various types of active materials used for the detection of ammonia, e.g., carbon nanotubes, carbon nanofibers, graphene, graphene oxide, and related materials. Different parameters that can affect the performance of chemiresistive gas sensors are discussed. The paper also gives a comparison of the sensing characteristics (response, response time, recovery time, operating temperature) of gas sensors based on carbon nanomaterials. The results of our tests on ammonia gas sensors using various techniques are analyzed. The problems related to the recovery of sensors using various approaches are also considered. Finally, the impact of relative humidity on the sensing behavior of carbon nanomaterials of various different natures was estimated.

Highly Reliable Organic Field-Effect Transistors with Molecular Additives for a High-Performance Printed Gas Sensor

Organic semiconductors (OSCs) are promising sensing materials for printed flexible gas sensors. However, OSCs are unstable in the humid air, which limits the realization of gas sensors for multiple usages. In this paper, we report a facile and effective way to improve the air stability of an OSC film to realize multiple reversibly used printed gas sensors by adding molecular additives. The tetracyanoquinodimethane (TCNQ) or 4-aminobenzonitrile (ABN) additives effectively prevent adsorption of moisture from the air on the OSC layer, thereby providing a stable gas sensor operation. The organic field-effect transistor (OFET)-based indacenodithiophene-co-benzothiadiazole with TCNQ or ABN shows highly reliable ammonia (NH₃) gas sensing up to 10 ppm in air, with 23.14% sensitivity, and the gas sensor signal can recover up to 100%. In particular, the stability of gas detection is greatly improved by the additives, which can be performed in the air for 16 days. The result indicates that the elimination of moisture trapped in OSCs with molecule additives is critical in the improvement of device air/operational stabilities and the achievement of high-performance OFET-based gas sensors.

Breath Ammonia Is a Useful Biomarker Predicting Kidney Function in Chronic Kidney Disease Patients

Chronic kidney disease (CKD) is a public health problem and its prevalence has increased worldwide; patients are commonly unaware of the condition. The present study aimed to investigate whether exhaled breath ammonia via vertical-channel organic semiconductor (V-OSC) sensor measurement could be used for rapid CKD screening. We enrolled 121 CKD stage 1–5 patients, including 19 stage 1 patients, 26 stage 2 patients, 38 stage 3 patients, 21 stage 4 patients, and 17 stage 5 patients, from July 2019 to January 2020. Demographic and laboratory data were recorded. The exhaled ammonia was collected and rapidly measured by the V-OSC sensor to correlate with kidney function. Results showed no significant difference in age, sex, body weight, hemoglobin, albumin level, and comorbidities in different CKD stage patients. Correlation analysis demonstrated a good correlation between breath ammonia and blood urea nitrogen levels, serum creatinine levels, and estimated glomerular filtration rate (eGFR). Breath ammonia concentration was significantly elevated with increased CKD stage compared with the previous stage (CKD stage 1/2/3/4/5: 636 ± 94; 1020 ± 120; 1943 ± 326; 4421 ± 1042; 12781 ± 1807 ppb, p < 0.05). The receiver operating characteristic curve analysis showed an area under the curve (AUC) of 0.835 (p < 0.0001) for distinguishing CKD stage 1 from other CKD stages at 974 ppb (sensitivity, 69%; specificity, 95%). The AUC was 0.831 (p < 0.0001) for distinguishing between patients with/without eGFR < 60 mL/min/1.73 m² (cutoff 1187 ppb: sensitivity, 71%; specificity, 78%). At 886 ppb, the sensitivity increased to 80% but the specificity decreased to 69%. This value is suitable for kidney function screening. Breath ammonia detection with V-OSC is a real time, inexpensive, and easy to administer measurement device for screening CKD with reliable diagnostic accuracy.

Clinical, Operative, and Economic Outcomes of the Point-of-Care Blood Gases in the Nephrology Department of a Third-Level Hospital

CONTEXT.—

Point-of-care testing allows rapid analysis and short turnaround times. To the best of our knowledge, the present study assesses, for the first time, clinical, operative, and economic outcomes of point-of-care blood gas analysis in a nephrology department.

OBJECTIVE.—

To evaluate the impact after implementing blood gas analysis in the nephrology department, considering clinical (differences in blood gas analysis results, critical results), operative (turnaround time, elapsed time between consecutive blood gas analysis, preanalytical errors), and economic (total cost per process) outcomes.

DESIGN.—

A total amount of 3195 venous blood gas analyses from 688 patients of the nephrology department before and after point-of-care blood gas analyzer installation were included. Blood gas analysis results obtained by ABL90 FLEX PLUS were acquired from the laboratory information system. Statistical analyses were performed using SAS 9.3 software.

RESULTS.—

During the point-of-care testing period, there was an increase in blood glucose levels and a decrease in pCO2, lactate, and sodium as well as fewer critical values (especially glucose and lactate). The turnaround time and the mean elapsed time were shorter. By the beginning of this period, the number of preanalytical errors increased; however, no statistically significant differences were found during year-long monitoring. Although there was an increase in the total number of blood gas analysis requests, the total cost per process decreased.

CONCLUSIONS.—

The implementation of a point-of-care blood gas analysis in a nephrology department has a positive impact on clinical, operative, and economic terms of patient care.

Design and Synthesis of Air-Stable p-Channel-Conjugated Polymers for High Signal-to-Drift Nitrogen Dioxide and Ammonia Sensing

The development of high-performance-conjugated polymer-based gas sensors involves detailed structural tailoring such that high sensitivities are achieved without compromising the stability of the fabricated devices. In this work, we systematically developed a series of diketopyrrolopyrrole (DPP)-based polymer semiconductors by modifying the polymer backbone to achieve and rationalize enhancements in gas sensitivities and electronic stability in air. NO₂- and NH₃-responsive polymer-based organic field-effect transistors (OFETs) are described with improved air stability compared to all-thiophene conjugated polymers. Five DPP-fluorene-based polymers were synthesized and compared to two control polymers and used as active layers to detect a concentration of NO₂ at least as low as 0.5 ppm. The hypothesis that the less electron-donating fluorene main-chain subunit would lead to increased signal/drift compared to thiophene and carbazole subunits was tested. The sensitivities exhibited a bias voltage-dependent behavior. The proportional on-current change of OFETs using a dithienyl DPP-fluorene polymer reached ∼614% for an exposure to 20 ppm of NO₂ for 5 min, testing at a bias voltage of -33 V, among the higher reported NO₂ sensitivities for conjugated polymers. Electronic and morphological studies reveal that introduction of the fluorene unit in the DPP backbone decreases the ease of backbone oxidation and induces traps in the thin films. The combination of thin-film morphology and oxidation potentials governs the gas-absorbing properties of these materials. The ratio of responses on exposure to NO₂ and NH₃ compared to drifts while taking the device through repeated gate voltage sweeps is the highest for two polymers incorporating electron-donating linkers connecting the DPP and thiophene units in the backbone, in this category of organic semiconductors. The responses to NO₂ were much larger than that to NH₃, indicating increased susceptibility to oxidizing vs reducing gases, and that the capability of oxidizing gases to induce additional charge density has a more dramatic electronic effect than when reducing gases create traps. This work demonstrates the capability of achieving improved stability with the retention of high sensitivity in conjugated polymer-based OFET sensors by modulating redox and morphological properties of polymer semiconductors by structural control.

Nanomaterial-based gas sensors used for breath diagnosis

Gas-sensing applications commonly use nanomaterials (NMs) because of their unique physicochemical properties, including a high surface-to-volume ratio, enormous number of active sites, controllable morphology, and potential for miniaturisation.

Polymer-based flexible NOx sensors with ppb-level detection at room temperature using breath-figure molding

A strategically designed polymer semiconductor thin film morphology with both high responsivity to the specific gas analyte and high signal transport efficiency is reported to realize high-performance flexible NOx gas sensors. Breath-figure (BF) molding of polymer semiconductors enables a finely defined degree of nano-porosity in polymer films with high reproducibility while maintaining high charge carrier mobility characteristics of organic field effect transistors (OFETs). The optimized BF-OFET with a donor-acceptor copolymer exhibits a maximum responsivity of over 104%, sensitivity of 774% ppm-1, and limit of detection (LOD) of 110 ppb against NO at room temperature. When tested across at NO concentrations of 0.2-10 ppm, the BF-OFET gas sensor exhibits a response time of 100-300 s, which is suitable for safety purposes in practical applications. Furthermore, BF-OFETs show a high reproducibility as confirmed by statistical analysis on 64 independently fabricated devices. The selectivity of NOx analytes is tested by comparing the sensing ability of BF-OFETs with those of other reducing gases and volatile organic compounds; the BF-OFET gas sensor platform monitors specific gas analytes based on their polarity and magnitude of sensitivity. Finally, flexible BF-OFETs conjugated with plastic substrates are demonstrated and they exhibit a sensitivity of 500% ppm-1 and a LOD of 215 ppb, with a responsivity degradation of only 14.2% after 10 000 bending cycles at 1% strain.