QCM Measurements of RH with Nanostructured Carbon-Based Materials: Part 2-Experimental Characterization

In this series of two papers, the humidity sensing of a carbon nanotube (CNT) network-based material is transduced and studied through quartz crystal microbalance (QCM) measurements. To this aim, quartzes functionalized with different amounts of sensing material were realized, exposed to different humidity levels, and characterized. In this second paper, the experimental results are presented and discussed. The sensing mechanisms are elucidated exploiting the theory presented in the first paper of this series. The presented results show that the investigated material functionalization induces a large response of QCM to humidity in terms of resonant frequency even at low RH levels, with a sensitivity of about 12 Hz/%RH (at RH < 30% and room temperature and 10 ug of deposited SWCNT solution) and an increase in sensitivity in the high RH range typical of nanostructured film. Regarding the response in terms of motional resistance, a large response is obtained only at intermediate and high humidity levels, confirming that condensation of water in the film plays an important role in the sensing mechanism of nanostructured materials

A review of nanocomposite-modified electrochemical sensors for water quality monitoring

Electrochemical sensors play a significant role in detecting chemical ions, molecules, and pathogens in water and other applications. These sensors are sensitive, portable, fast, inexpensive, and suitable for online and in-situ measurements compared to other methods. They can provide the detection for any compound that can undergo certain transformations within a potential window. It enables applications in multiple ion detection, mainly since these sensors are primarily non-specific. In this paper, we provide a survey of electrochemical sensors for the detection of water contaminants, i.e., pesticides, nitrate, nitrite, phosphorus, water hardeners, disinfectant, and other emergent contaminants (phenol, estrogen, gallic acid etc.). We focus on the influence of surface modification of the working electrodes by carbon nanomaterials, metallic nanostructures, imprinted polymers and evaluate the corresponding sensing performance. Especially for pesticides, which are challenging and need special care, we highlight biosensors, such as enzymatic sensors, immunobiosensor, aptasensors, and biomimetic sensors. We discuss the sensors’ overall performance, especially concerning real-sample performance and the capability for actual field application

Human Breathing Monitoring by Graphene Oxide Based Sensors

Non-invasive monitoring of human health is of a high importance for early detection of illnesses and improving life quality. Breath monitoring is important for detection of severe diseases such as lung cancer or sleep apnea. In this work, we introduce a breath sensor based on a graphene oxide film deposited on silver interdigitated electrode and a flexible substrate. The graphene oxide film was then thermally annealed to partially reduce the graphene oxide. The measurements of sensor impedance carried out at different humidity levels show a high decrease by several orders of magnitudes by increasing the relative humidity. Sensitivity to humid air results from the high hydrophilicity of the graphene oxide due to its oxygen functional groups. The change of transport mechanism from Nyquist plot shows the change of the sensor impedance from the capacitive behavior to a semicircle of parallel resistance and capacitance. The sensors show an ultrahigh sensitivity to humidity at high humidity values, a very low response time of less than one second and an excellent repeatability of the measurements. For tracking human breathing, the reaction on natural breathing was acquired by a digital oscilloscope together with an IoT mobile application to visualize the results in real time and store them for further processing. The sensor performance shows that it is suitable as a noninvasive and flexible breath-monitoring sensor system. The proposed sensor can be a step to flexible and cheap wearable sensors for detection of human breath and hazardous breath airborne such as COVID-19

Modeling the conductivity response to NO2 gas of films based on MWCNT networks

This work proposes a model describing the dynamic behavior of sensing films based on functionalized MWCNT networks in terms of conductivity when exposed to time-variable concen-trations of NO2 and operating with variable working temperatures. To test the proposed model, disordered networks of MWCNTs functionalized with COOH and Au nanoparticles were exploited. The model is derived from theoretical descriptions of the electronic transport in the nanotube net-work, of the NO2 chemisorption reaction and of the interaction of these two phenomena. The model is numerically implemented and then identified by estimating all the chemical/physical quantities involved and acting as parameters, through a model fitting procedure. Satisfactory results were obtained in the fitting process, and the identified model was used to further the analysis of the MWCNT sensing in dynamical conditions

Health monitoring of human breathing by graphene oxide based sensors

Monitoring of human health is of high importance to enable early detection of illness and improve the quality of life from diseases such as lung cancer or sleep apnea. Breath monitoring is highly interesting in this regard. Graphene oxide is one of the most studied materials for sensing applications and has exceptional properties like large surface area, mechanical stability, and tunable electrical properties. In this paper, we introduce a breath sensor made of a graphene oxide film. Graphene oxide dispersion was deposited on silver interdigitated electrode on flexible substrate, which was then thermally annealed to partially reduce the graphene oxide. The breathing signal was acquired by a digital oscilloscope and the data saved using a LabVIEW interface. The sensors show ultra low response time of less than one second and excellent repeatability. Impedance spectroscopy measurements were carried out at different humidity levels to characterize the sensor. The sensor impedance shows a high decrease by several orders of magnitudes by increasing the relative humidity. Sensitivity to humid air results from the high hydrophilicity of the graphene oxide due to its oxygen functional groups. The change of transport mechanism from Nyquist plot shows the change of the sensor impedance from the capacitive behavior to a semicircle of parallel resistance and capacitance. The high sensitivity of GO to humid air as well as the ultrafast response makes it suitable as a noninvasive and flexible breath-monitoring sensor

Original Structural and Electrical Investigation for a new BG-F-6 vitreous bio-ceramic as Humidity Sensors

International audienceTwo biomaterial types have been the focus of sensor applications: Fluorosilicate bioactive Glass BG-F-6 crude and compact. Of the two, BG-F-6 compact material show the greater mechanical strength, and electrical behaviour provoke greater humidity sensing capacity. Thus, the glassy discs show great potential for deployment in a new generation of biosensors and environment requires. The aim of this paper is to develop a material that combines an interesting mechanical strength, monophasic stability with potential thermic resistance and great electrical capacity. By returning to its high temperature synthesis protocol, makes this fluorosilicate glass an attractive material for sensors development topic and environmental precautions

Highly sensitive detection of NO2 by au and TiO2 nanoparticles decorated SWCNTs sensors

The aim of this work is to investigate the gas sensing performance of single wall carbon nanotubes (SWCNTs)-based conductive sensors operating at low–medium temperatures (<250 °C). The investigated sensing films consists of an SWCNT network obtained by drop-casting a SWCNT suspension. Starting from this base preparation, different sensing devices were obtained by decorating the SWCNT network with materials suitable for enhancing the sensitivity toward the target gas. In particular, in this paper, nano-particles of gold and of TiO2 were used. In the paper, the performance of the different sensing devices, in terms of response time, sensitivity toward NO2 and cross-sensitivity to O2, CO and water vapor, were assessed and discussed. Sensors based on decorated SWCNT films showed high performance; in particular, the decoration with Au nanoparticles allows for a large enhancement of sensitivity (reaching 10%/1 ppm at 240 °C) and a large reduction of response time. On the other hand, the addition of TiO2 nanoparticles leads to a satisfactory improvement of the sensitivity as well as a significant reduction of the response time at moderate temperatures (down to 200 °C). Finally, the suitability of using Au decorated SWCNTs-based sensors for room temperature sensing is demonstrated