Mesoporous cellulose nanofibers-interlaced PEDOT:PSS hybrids for chemiresistive ammonia detection

Carbon dots and cellulose nanocrystal-incorporated chitosan composite films with enhanced gas selectivity and photodynamic antibacterial properties for fruit preservation

Winter jujube is prone to rapid ripening and deterioration during postharvest storage and transportation. This study developed a multifunctional chitosan (CS) composite film incorporating dialdehyde cellulose nanocrystal (DCNC) and carbon dots (CDs) derived from walnut green husks. DCNC functioned as cross-linking filler, while CDs served as active nanofillers. The CS composite film containing 3 wt% DCNC and 3 wt% CDs (CS/DCNC/CDs-3 %) exhibited significant improvements in UV-blocking, mechanical strength, gas barrier, and thermal stability, attributing to the formation of a dense film structure and synergistic effect of Schiff base and hydrogen bonding interactions among film components. Notably, this composite film demonstrated a high CO2/O2 selectivity of 14.1, facilitating the creation of an ideal atmosphere inside the package. This composite film exhibited remarkable antioxidant activity and displayed potent antibacterial capacity through photocatalytic ROS generation, achieving inhibition rates of 90.8 % against S. aureus and 86.8 % against E. coli. Additionally, this film showed favorable biosafety and biodegradability, addressing food safety and environmental concerns. Postharvest preservation tests confirmed that this film assisted by light exposure effectively regulated physiological metabolism and delayed the ripening of winter jujube, highlighting its potential as an active modified atmosphere packaging material for perishable fruit preservation.

Advances in cellulose-based self-powered ammonia sensors

Ammonia sensors are widely used across applications in food monitoring, environmental surveillance, and medical research, where high safety standards are essential. Cellulose-based materials are particularly well-suited to meet these stringent requirements, with significant potential for innovation due to their biodegradability and biocompatibility. Of the various cellulose-based ammonia sensors available, self-powered sensors, especially those based on triboelectric nanogenerators (TENGs), stand out for their unique advantages, including the absence of an external power supply, environmental sustainability, and ease of integration. This review offers a detailed overview of the integration of cellulose-based materials with ammonia-sensitive components, highlighting their ease of processing and modification. It further classifies and compares cellulose-based ammonia sensors based on their sensing mechanisms, emphasizing TENG-based sensors specifically. The review concludes with a summary of current applications and explores optimization strategies. Finally, it discusses future opportunities and challenges for cellulose-based self-powered ammonia sensors and provides valuable insights into ongoing innovation and potential.

Enhanced room temperature ammonia gas sensing based on a multichannel PSS-functionalized graphene/PANI network

Disordered polymerization of polymers widens the polymerization degree distribution, which leads to uncontrollable thickness and significantly weakens their sensing performance. Herein, poly(sodium p-styrenesulfonate)-functionalized reduced graphene oxide (PSS-rGO) with multichannel chain structures coated with thin polyaniline layer (PSS-rGO/PANI) nanocomposites was synthesized via a facile interfacial polymerization route. The morphology and microstructure of the PSS-rGO/PANI nanocomposites were characterized using Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The flexible PSS-rGO/PANI-2 sensor exhibits excellent room temperature NH3 sensing performance, including a higher sensitivity of 362% and a faster response/recovery time of 23/158 s towards 100 ppm NH3 than other PSS-rGO/PANI nanocomposites. In addition, the flexible PSS-rGO/PANI-2 sensor has a low detection limit of 10 ppb, superior selectivity, repeatability, and long-term stability over 75 days. Remarkably, the flexible PSS-rGO/PANI-2 sensor shows excellent humidity resistance (196 ± 3%, 50 ppm) even at a high relative humidity of 80%. The gas sensing mechanism was systematically investigated through high protonation states and strong π-π conjugation of PSS-rGO/PANI. This work provides a convenient method to construct multichannel thin polyaniline layer-coated graphene nanocomposites and promotes their application in flexible wearable electronics.

Room temperature gas sensors for NH3 detection based on the heterojunction of 2D Ti3C2Tx MXenes and Bi2S3

Bi2S3/Ti3C2Tx nanomaterials were successfully prepared through a simple hydrothermal method. Various methods were used for their characterization, including XRD, XPS, SEM, EDS, and BET, along with testing their gas-sensing properties. The results showed that the response value to 100 ppm ammonia at room temperature reached 107%, which was 14.1 times higher than that of pure few-layer MXene. After undergoing anti-humidity interference testing, we observed that Bi2S3/Ti3C2Tx exhibited a higher response value in real-time monitoring of ammonia as humidity increased. Specifically, under 90% humidity conditions, its response value reached 1.32 times that of normal humidity conditions. This exceptional moisture resistance ensures that the sensor can maintain stability, and even exhibit superior performance, in harsh environments. Therefore, it possesses excellent selectivity, high-moisture-resistance, and long-term stability, making it significant in the field of medical and health monitoring.

Core-Shell PEDOT-PVDF Nanofiber-Based Ammonia Gas Sensor with Robust Humidity Resistance

Current ammonia sensors exhibit cross-sensitivity to water vapor, leading to false alarms. We developed a core-shell nanofiber (CSNF) structure to address these issues, using conductive poly(3,4-ethylenedioxythiophene) (PEDOT) as the core and hydrophobic polyvinylidene fluoride-tetrafluoroethylene (PVDF-TrFE) as the shell. The PEDOT-PVDF CSNF, with a diameter of ~500 nm and a 300 nm thick PVDF layer, showed a superior sensitivity and humidity resistance compared to conventional PEDOT membranes for ammonia concentrations of 10-100 ppm. In humid environments, CSNF sensors outperformed membrane sensors, exhibiting a tenfold increase in performance at 51% relative humidity (RH). This study highlights the potential of CSNF sensors for practical ammonia detection, maintaining a high performance under varying humidity levels.

Meshed, Flexible, and Self-Supported Humidity Sensors by Direct-Writing with Multifunctional Applications

Flexibility endows humidity sensors with new applications in human health monitoring except for traditionally known environmental humidity detection in recent years. In this study, a flexible, mesh-structured, and self-supported humidity sensor was designed and manufactured by direct writing in a homemade two-dimensional stepping numerical control workstation. Bacterial cellulose with humidity sensitivity and good film-forming properties was applied as the self-supporting substrate, in which conductive activated carbon and water-absorptive magnesium chloride (MgCl2) were incorporated. The humidity sensing performance of the printed sensor was measured and optimized. Besides, the fundamental insight into the sensing mechanism of the printed humidity sensor was analyzed by a complex impedance spectrum. The multifunctional applications of the self-supported humidity sensor were demonstrated by human breathing detection, noncontact distance sensing, and speaking recognition. The simple self-supported structure combined with the meshed attribute of the flexible sensor showed large use potential in real-time monitoring of human respiration, voice detection, environmental humidity monitoring, and noncontact switches.

Comparative Study of Electrochromic Supercapacitor Electrodes Based on PEDOT:PSS/ITO Fabricated via Spray and Electrospray Methods

PEDOT

PSS stands out as a leading commercial conducting polymer due to its excellent water dispersibility, controllable miscibility, adjustable conductivity, and ability to form films through various techniques. This study investigates the electrochemical and electrochromic performance of electrodes prepared by depositing PEDOT:PSS onto ITO surfaces by using two distinct methods: conventional spray coating and electrospray deposition. Detailed characterization of the prepared electrodes was performed by using atomic force microscopy, scanning electron microscopy, Fourier-transform infrared, and Raman spectroscopy techniques. Our findings reveal that electrodes fabricated via electrospray deposition (PEDOT:PSS/ITO electrode_2) significantly outperform those made by spray coating (PEDOT:PSS/ITO electrode_1). Specifically, electrode_2 exhibits a capacitance of 1678.60 μF cm-2, compared to 826.14 μF cm-2 for electrode_1, at a current density of 10 μA cm-2.

PEDOT

PSS electrodes exhibit areal energy densities of 0.41 and 0.84 mW h cm-2, along with power densities of 4.96 and 4.97 μW cm-2, respectively. Moreover, electrode_2 demonstrates a high coloration efficiency of 84.32 cm2 C-1 and fast response times of 1.36 s for coloration and 0.98 s for bleaching. This study highlights the advantages of electrospray deposition over traditional methods, showcasing the potential of electrospray-prepared PEDOT:PSS electrodes for use in multifunctional energy storage devices.

Ammonia detection: A pathway towards potential point-of-care diagnostics

Invasive methods such as blood collection and biopsy are commonly used for testing liver and kidney function, which are painful, time-consuming, require trained personnel, and may not be easily accessible to people for their routine checkup. Early diagnosis of liver and kidney diseases can prevent severe symptoms and ensure better management of these patients. Emerging approaches such as breath and sweat analysis have shown potential as non-invasive methods for disease diagnosis. Among the many markers, ammonia is often used as a biomarker for the monitoring of liver and kidney functions. In this review we provide an insight into the production and expulsion of ammonia gas in the human body, the different diseases that could potentially use ammonia as biomarker and analytical devices such as chemiresistive gas sensors for non-invasive monitoring of this gas. The review also provides an understanding into the different materials, doping agents and substrates used to develop such multifunctional sensors. Finally, the current challenges and the possible future trends have been discussed.

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.

PDMS Film-Based Flexible Pressure Sensor Array with Surface Protruding Structure for Human Motion Detection and Wrist Posture Recognition

Flexible pressure sensors have been widely concerned because of their great application potential in the fields of electronic skin, human-computer interaction, health detection, and so on. In this paper, a flexible pressure sensor is designed, with polydimethylsiloxane (PDMS) films with protruding structure as elastic substrate and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS)/cellulose nanocrystals (CNC) as conductive-sensitive material. The flexible pressure sensor has a wide linear detection range (0-100 kPa), outstanding sensitivity (2.32 kPa-1), and stability of more than 2000 cycles. The sensor has been proven to be able to detect a wide range of human movements (finger bending, elbow bending, etc.) and small movements (breathing, pulse, etc.). In addition, the pressure sensor array can detect the pressure distribution and judge the shape of the object. A smart wristband equipped with four flexible pressure sensors is designed. Among them, the k-nearest neighbor (KNN) algorithm is used to classify sensor data to achieve high accuracy (99.52%) recognition of seven kinds of wrist posture. This work provides a new opportunity to fabricate simple, flexible pressure sensors with potential applications in the next-generation electronic skin, health detection, and intelligent robotics.

Alkalized Cellulose Nanofiber-Interweaved PEDOT:PSS Thin-Film Sensors via Layer-by-Layer Spraying Assembly for Ultrafast Molecular Ammonia Detection

As a typical representative of conductive polymers (CPs), poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) is intensively employed for chemiresistive ammonia (NH3) sensing on account of its favorable aqueous solubility, benign environmental stability, and outstanding room-temperature conductivity; however, it is severely plagued by low sensitivity and sluggish reaction kinetics. To circumvent these limitations, the guest-alkalized cellulose nanofibers (AC) were introduced into the host PEDOT:PSS matrix by the layer-by-layer spraying assembly method (LBLSA) in this work. The componential proportion-optimized PEDOT:PSS/AC/PEDOT:PSS (P/AC/P) sensor delivered a large sensitivity of 20.2%/ppm within 0.1-3 ppm of NH3 at 21 °C@26% RH, an experimental limit of detection (LoD) as low as 30 ppb, a high response of 18.1%, and a short response/recovery times (4.8/4.0 s) toward 1 ppm of NH3, which ranked among the best cases thus far. Also, excellent repeatability and long-term stability and selectivity were demonstrated. Meanwhile, the flexible P/AC/P sensors worked well under various bending angles and bending times. This work combines a green material system and a facile film deposition method to overcome the liquid dispersion incompatibility when preparing a multicomponent mixture for swift trace NH3 detection. The universality and extensibility of this methodology endow a broad prospect in the field of future wearable optoelectronic systems.

Thin Films of Polyaniline-Based Nanocomposites with CeO2 and WO3 Metal Oxides Applied to the Impedimetric and Capacitive Transducer Stages in Chemical Sensors

There is a recognized need for the development of cost-effective, stable, fast, and optimized novel materials for technological applications. Substantial research has been undertaken on the role of polymeric nanocomposites in sensing applications. However, the use of PANI-based nanocomposites in impedimetric and capacitive electrochemical sensors has yet to be understood. The present study aimed to explore the relationship between the sensitivity and linearity of electrochemical pH sensors and the composition of nanocomposites. Thin films of PANI/CeO₂ and PANI/WO₃ were deposited via spin coating for characterization and application during the electrochemical impedance and capacitance spectroscopy (EIS and ECS) transduction stages. The findings showed that the optimized performance of the devices was extended not only to the sensitivity but also to the linearity. An increase of 213% in the ECS sensitivity of the PANI/CeO₂ compared to the metal oxide and an increase of 64% in the ECS linearity of the PANI/WO₃ compared to the polymeric sensitivity were reported. This study identified the structure-property relationship of nanocomposite thin films of PANI with metal oxides for use in electrochemical sensors. The developed materials could be applied in devices to be used in different fields, such as food, environment, and biomedical monitoring.