The reliable detection of ammonia at room temperature is crucial for not only maintaining environmental safety but also for reducing the risks of hazardous pollutants. In this study, the electrochemical modification of laser-induced graphene (LIG) with polyaniline (PANI) led to the development of a chemo-resistive nanocomposite (PANI@LIG) for detecting ammonia levels at room temperature. The composite is characterized by field emission scanning electron microscopy, Fourier transforms infrared, and Raman and X-ray photoelectron spectroscopy. This work marks the first utilization of PANI@LIG for gas sensing and introduces a simple but effective approach for fabricating low-cost wearable gas sensors with high sensitivity and flexibility.

The electrochemical synthesis of polypyrrole (PPy) on laser-induced graphene (LIG) electrodes is investigated in this study, along with the gas sensing applications of these modified laser-tailored materials. A simple and scalable method for the low-cost, large-scale production of polypyrrole LIG nanocomposites (PPy@LIG NCs) is proposed. This nanocomposite is subsequently applied to design chemo-resistive flexible gas sensors to detect ammonia (NH3) levels at room temperature. Following a brief gas exposure, PPy@LIG NCs sensors demonstrate changes in resistance with a sensitivity 14 times higher than that of pure LIG. Moreover, excellent repeatability in results and a low detection limit of 1 ppm were achieved. The LIG formation and electrochemical synthesis of PPy were confirmed through Raman spectroscopy and FTIR spectroscopy. The analysis by FE-SEM and TEM verified the formation of PPy@LIG NCs. In conclusion, this work introduces the novel PPy@LIG nanocomposites and its application in gas sensing, showcasing their unique selectivity, enhanced sensitivity, and cost-effective production. These attributes mark a significant step forward, presenting new possibilities for the development of advanced gas-sensing systems aimed at improving air quality monitoring.

This paper presents the integration of a sensing layer over interdigitated electrodes and an electronic circuit on the same flexible printed circuit board. This integration provides an effective technique to use this design as a wearable gas measuring system in a target application, exhibiting high performance, low power consumption, and being lightweight for on-site monitoring. The wearable system proves the concept of using an NFC tag combined with a chemoresistive gas sensor as a cumulative gas sensor, having the possibility of holding the data for a working day, and completely capturing the exposure of a person to NO₂ concentrations. Three different types of sensors were tested, depositing the sensing layers on gold electrodes over Kapton substrate: bare graphene, graphene decorated with 5 wt.% zinc oxide nanoflowers, or nanopillars. The deposited layers were characterized using FESEM, EDX, XRD, and Raman spectroscopy to determine their crystalline structure, morphological and chemical compositions. The gas sensing performance of the sensors was analyzed against NO₂ (dry and humid conditions) and other interfering species (dry conditions) to check their sensitivity and selectivity. The resultant-built wearable NFC tag system accumulates the data in a non-volatile memory every minute and has an average low power consumption of 24.9 µW in dynamic operation. Also, it can be easily attached to a work vest.

Manganese dioxide (MnO₂) has drawn attention as a sensitiser to be incorporated in graphene-based chemoresistive sensors thanks to its promising properties. In this regard, a rGO@MnO₂ sensing material was prepared and deposited on two different substrates (silicon and Kapton). The effect of the substrate nature on the morphology and sensing behaviour of the rGO@MnO₂ material was thoroughly analysed and reported. These sensors were exposed to different dilutions of NO₂ ranging from 200 ppb to 1000 ppb under dry and humid conditions (25% RH and 70% RH) at room temperature. rGO@MnO₂ deposited on Kapton showed the highest response of 6.6% towards 1 ppm of NO₂ under dry conditions at RT. Other gases or vapours such as NH₃, CO, ethanol, H₂ and benzene were also tested. FESEM, HRTEM, Raman, XRD and ATR-IR were used to characterise the prepared sensors. The experimental results showed that the incorporation of nanosized MnO₂ in the rGO material enhanced its response towards NO₂. Moreover, this material also showed very good responses toward NH₃ both under dry and humid conditions, with the rGO@MnO₂ sensor on silicon showing the highest response of 18.5% towards 50 ppm of NH₃ under 50% RH at RT. Finally, the synthetised layers showed no cross-responsiveness towards other toxic gases.

This work presents the design and setup of an IoT platform at level four of the technology readiness level (TRL-4), to detect, classify, and quantify pollutant gases. This study combines concepts such as wireless sensor networks, arrays of sensors, and multivariate data analysis to interface different nano-structured chemoresistor gas sensors. The IoT platform consists of several gas sensor nodes with Wi-Fi capability to send data from a sensor array to a server and its user interface. Each gas sensor node interfaces one sensor array (up to four chemoresistor gas sensors and one temperature and humidity sensor). The server channels the data from the gas sensor nodes to the user interface. The platform was set up following a two-stage methodology. First (training stage), sensor data was received, stored, and used to train different multilayer perceptron (MLP) artificial neural networks (ANNs). Second (recognition stage), models were implemented in the user interface to classify and quantify the presence of pollutants. The platform was tested in laboratory conditions under exposure to nitrogen dioxide and ammonia at different % RH. As a result, the platform improves the classification and quantification times compared with the single-sensor approach. Additionally, the system was evaluated using a gas mixture of both gases, showing a classification accuracy exceeding 99 %. Likewise, the training and recognition stages can be repeated to add new chemoresistor gas sensors in the node, add new nodes to the platform, and deploy the nodes in different scenarios.

Manganese dioxide (MnO2) has drawn attention as a sensitizer to be incorporated in graphene-based chemoresistive sensors thanks to its promising properties. In this regard, a rGO@MnO2 sensing material was prepared and deposited on two different substrates (Silicon and Kapton). These sensors were exposed to different dilutions of NO2 under dry and humid conditions at room temperature. Other gases or vapours such as NH3, CO, ethanol and H2 were also tested. FESEM, HRTEM, RAMAN and XRD were used to characterize the prepared sensors. The experimental results showed that the incorporation of MnO2 in the rGO material enhanced its response towards NO2. Moreover, this material showed also very good responses toward NH3 both under dry and humid conditions and showed no cross-responsiveness towards other toxic gases.