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A special issue of Chemosensors (ISSN 2227-9040). This special issue belongs to the section "Nanostructures for Chemical Sensing".

Deadline for manuscript submissions: closed (15 February 2022) | Viewed by 37516

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Prof. Dr. Valerio Vignoli

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DIISM – University of Siena, via Roma 56 – 53100 Siena, Italy
Interests: analog and digital electronic design; design, characterization, and modeling of advanced sensors for monitoring physical quantities; development of data acquisition and processing systems

Dr. Enza Panzardi

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Department of Information Engineering and Mathematics, Università degli Studi di Siena, 53100 Siena, Italy
Interests: physical sensors; chemical sensors; gas sensors; measurement systems
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Special Issue Information

Dear Colleagues,

In recent decades, a large amount of research work has been devoted to understanding the sensing mechanism of gas sensors. In most cases, e.g., metal oxide sensors, the sensing principle is understood in its essential features, but an exhaustive knowledge of their behavior has not yet been achieved in general.

Reliable chemical–physical dynamic models for gas sensors can speed up the development of the related measurement systems, allowing to replace experimental tuning with simulations and to achieve better performance. Moreover, the comparison of the model outputs with experimental data helps in general to understand the behavior of the sensors themselves, e.g., by exploring the relevance of the different mechanisms involved in sensing or assessing the validity of specific assumptions.

The development of a gas sensor dynamic model is strictly related to the techniques used for sensor characterization: from this point of view, there is a wide range of possibilities, each open to different implementations, depending on the specific sensor and operation conditions (consider, for example, temperature modulation).

The aim of this Special Issue is to highlight recent advances in these fields, with reference to the different families of devices that can be used for gas sensing. Authors are therefore invited to submit works dealing with simulations, modeling, and characterization for resistive, electrochemical, optical, mass-variation, and any other type of gas sensors, also with reference to results obtained with new gas sensor materials. Both review articles and research papers are welcome.

Dr. Valerio Vignoli
Dr. Enza Panzardi
Guest Editors

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Published Papers (12 papers)

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11 pages, 5639 KiB

Open AccessArticle

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

by Ada Fort, Anna Lo Grasso, Marco Mugnaini, Enza Panzardi, Lorenzo Parri, Valerio Vignoli, Cecilia Viti, Ammar Al-Hamry and Olfa Kanoun

Chemosensors 2022, 10(8), 320; https://doi.org/10.3390/chemosensors10080320 - 10 Aug 2022

Cited by 2 | Viewed by 1830

Abstract

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. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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13 pages, 4315 KiB

Open AccessArticle

QCM Measurements of RH with Nanostructured Carbon-Based Materials: Part 1—Theory and Model

by Ada Fort, Anna Lo Grasso, Marco Mugnaini, Enza Panzardi and Valerio Vignoli

Chemosensors 2022, 10(8), 315; https://doi.org/10.3390/chemosensors10080315 - 7 Aug 2022

Cited by 6 | Viewed by 1855

Abstract

In this series of two papers, the humidity sensing of a carbon nanotube’s (CNTs) network-based material is studied through quartz crystal microbalance (QCM) sensors. To this aim, quartzes functionalized with different amounts of sensing material were realized, exposed to different humidity levels, and characterized. In this first paper, the theoretical framework is presented, whereas the second one presents the experimental study. This paper discusses at first the water adsorption and desorption on single-wall carbon nanotube (SWCNT) networks, and subsequently deeply investigates the behavior of QCM-based measurements. Numerical simulations based on the equivalent electrical model of the quartz were used for predicting the vibrational behavior of functionalized QCMs when exposed to different humidity levels, accounting for the effect of the different water adsorption mechanisms: chemisorption, physisorption, and capillary condensation. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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21 pages, 984 KiB

Open AccessArticle

Neural Network Robustness Analysis Using Sensor Simulations for a Graphene-Based Semiconductor Gas Sensor

by Sebastian A. Schober, Yosra Bahri, Cecilia Carbonelli and Robert Wille

Chemosensors 2022, 10(5), 152; https://doi.org/10.3390/chemosensors10050152 - 21 Apr 2022

Cited by 9 | Viewed by 3107

Abstract

Despite their advantages regarding production costs and flexibility, chemiresistive gas sensors often show drawbacks in reproducibility, signal drift and ageing. As pattern recognition algorithms, such as neural networks, are operating on top of raw sensor signals, assessing the impact of these technological drawbacks on the prediction performance is essential for ensuring a suitable measuring accuracy. In this work, we propose a characterization scheme to analyze the robustness of different machine learning models for a chemiresistive gas sensor based on a sensor simulation model. Our investigations are structured into four separate studies: in three studies, the impact of different sensor instabilities on the concentration prediction performance of the algorithms is investigated, including sensor-to-sensor variations, sensor drift and sensor ageing. In a further study, the explainability of the machine learning models is analyzed by applying a state-of-the-art feature ranking method called SHAP. Our results show the feasibility of model-based algorithm testing and substantiate the need for the thorough characterization of chemiresistive sensor algorithms before sensor deployment in order to ensure robust measurement performance. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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22 pages, 7715 KiB

Open AccessArticle

UV-Activated NO₂ Gas Sensing by Nanocrystalline ZnO: Mechanistic Insights from Mass Spectrometry Investigations

by Artem Chizhov, Pavel Kutukov, Alexander Gulin, Artyom Astafiev and Marina Rumyantseva

Chemosensors 2022, 10(4), 147; https://doi.org/10.3390/chemosensors10040147 - 15 Apr 2022

Cited by 11 | Viewed by 2573

Abstract

In this work, the photostimulated processes of O₂ and NO₂ molecules with the surface of ZnO under UV radiation were studied by in situ mass spectrometry in the temperature range of 30–100

^{\circ}

C. Nanocrystalline needle-like ZnO was synthesized by decomposition [...] Read more.

In this work, the photostimulated processes of O₂ and NO₂ molecules with the surface of ZnO under UV radiation were studied by in situ mass spectrometry in the temperature range of 30–100

^{\circ}

C. Nanocrystalline needle-like ZnO was synthesized by decomposition of basic zinc carbonate at 300

^{\circ}

C, and the surface concentration of oxygen vacancies in it were controlled by reductive post-annealing in an inert gas at 170

^{\circ}

C. The synthesized materials were characterized by XRD, SEM, low-temperature nitrogen adsorption (BET), XPS, Raman spectroscopy, and PL spectroscopy. Irradiation of samples with UV light causes the photoabsorption of both O₂ and NO₂. The photoadsorption properties of ZnO are compared with its defective structure and gas-sensitive properties to NO₂. A model of the sensor response of ZnO to NO₂ under UV photoactivation is proposed. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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12 pages, 2966 KiB

Open AccessArticle

Design and Characterization of a Microwave Transducer for Gas Sensing Applications

by Giovanni Gugliandolo, Krishna Naishadham, Giovanni Crupi and Nicola Donato

Chemosensors 2022, 10(4), 127; https://doi.org/10.3390/chemosensors10040127 - 29 Mar 2022

Cited by 8 | Viewed by 2654

Abstract

Gas sensors have wide applications in several fields, spanning diverse areas such as environmental monitoring, healthcare, defense, and the evaluation of personal and occupational exposure to hazardous chemicals. Different typologies of gas sensors have been proposed over the years, such as optical, electrochemical, and metal oxide gas sensors. In this paper, a relatively new typology of gas sensors is explored: the microwave gas sensor. It consists of a combination of a microwave transducer with a nanostructured sensing material deposited on an interdigitated capacitor (IDC). The device is designed and fabricated on a Rogers substrate (RO4003C) using microstrip technology, and investigated as a microwave transducer over the frequency range from 1 GHz to 6 GHz by measuring the scattering (S) parameters in response to gas adsorption and desorption. The sensing material is based on a nano-powder of barium titanate oxalate with a coating of urea (BaTiO(C₂O₄)₂/CO(NH₂)₂). It is deposited on the IDC surface by drop coating, thus creating a sensing film. The developed prototype has been tested toward different oxygen (O₂) concentrations and exhibits a sensitivity of 28 kHz/%O₂. Special attention has been devoted to the measurement process. Besides the canonical short-open-load-thru (SOLT) calibration of the measured S-parameters, a thru-reflect-line (TRL) calibration has been performed in order to get rid of the parasitic electromagnetic (EM) contributions of the board connectors and the feedlines, thus moving the measurement reference planes to the edges of the IDC. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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18 pages, 3016 KiB

Open AccessArticle

Flexible Impedimetric Electronic Nose for High-Accurate Determination of Individual Volatile Organic Compounds by Tuning the Graphene Sensitive Properties

by Tianqi Lu, Ammar Al-Hamry, José Mauricio Rosolen, Zheng Hu, Junfeng Hao, Yuchao Wang, Anurag Adiraju, Tengfei Yu, Elaine Yoshiko Matsubara and Olfa Kanoun

Chemosensors 2021, 9(12), 360; https://doi.org/10.3390/chemosensors9120360 - 15 Dec 2021

Cited by 20 | Viewed by 4174

Abstract

We investigated functionalized graphene materials to create highly sensitive sensors for volatile organic compounds (VOCs) such as formaldehyde, methanol, ethanol, acetone, and isopropanol. First, we prepared VOC-sensitive films consisting of mechanically exfoliated graphene (eG) and chemical graphene oxide (GO), which have different concentrations of structural defects. We deposited the films on silver interdigitated electrodes on Kapton substrate and submitted them to thermal treatment. Next, we measured the sensitive properties of the resulting sensors towards specific VOCs by impedance spectroscopy. We obtained the eG- and GO-based electronic nose composed of two eG films- and four GO film-based sensors with variable sensitivity to individual VOCs. The smallest relative change in impedance was 5% for the sensor based on eG film annealed at 180 °C toward 10 ppm formaldehyde, whereas the highest relative change was 257% for the sensor based on two-layers deposited GO film annealed at 200 °C toward 80 ppm ethanol. At 10 ppm VOC, the GO film-based sensors were sensitive enough to distinguish between individual VOCs, which implied excellent selectivity, as confirmed by Principle Component Analysis (PCA). According to a PCA-Support Vector Machine-based signal processing method, the electronic nose provided identification accuracy of 100% for individual VOCs. The proposed electronic nose can be used to detect multiple VOCs selectively because each sensor is sensitive to VOCs and has significant cross-selectivity to others. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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13 pages, 3580 KiB

Open AccessArticle

Sensor-Embedded Face Masks for Detection of Volatiles in Breath: A Proof of Concept Study

by Lorena Di Zazzo, Gabriele Magna, Martina Lucentini, Manuela Stefanelli, Roberto Paolesse and Corrado Di Natale

Chemosensors 2021, 9(12), 356; https://doi.org/10.3390/chemosensors9120356 - 12 Dec 2021

Cited by 10 | Viewed by 3195

Abstract

The correlation between breath volatilome and health is prompting a growing interest in the development of sensors optimized for breath analysis. On the other hand, the outbreak of COVID-19 evidenced that breath is a vehicle of infection; thus, the introduction of low-cost and disposable devices is becoming urgent for a clinical implementation of breath analysis. In this paper, a proof of concept about the functionalization of face masks is provided. Porphyrin-based sensors are among the most performant devices for breath analysis, but since porphyrins are scarcely conductive, they make use of costly and bulky mass or optical transducers. To overcome this drawback, we introduce here a hybrid material made of conducting polymer and porphyrins. The resulting material can be easily deposited on the internal surface of standard FFP face masks producing resistive sensors that retain the chemical sensitivity of porphyrins implementing their combinatorial selectivity for the identification of volatile compounds and the classification of complex samples. The sensitivity of sensors has been tested with respect to a set of seven volatile compounds representative of diverse chemical families. Sensors react to all compounds but with a different sensitivity pattern. Functionalized face masks have been tested in a proof-of-concept test aimed at identifying changes of breath due to the ingestion of beverages (coffee and wine) and solid food (banana- and mint-flavored candies). Results indicate that sensors can detect volatile compounds against the background of normal breath VOCs, suggesting the possibility to embed sensors in face masks for extensive breath analysis Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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14 pages, 3963 KiB

Open AccessArticle

Tetraphenylethylene-Substituted Bis(thienyl)imidazole (DTITPE), An Efficient Molecular Sensor for the Detection and Quantification of Fluoride Ions

by Ranjith Kumar Jakku, Nedaossadat Mirzadeh, Steven H. Privér, Govind Reddy, Anil Kumar Vardhaman, Giribabu Lingamallu, Rajiv Trivedi and Suresh Kumar Bhargava

Chemosensors 2021, 9(10), 285; https://doi.org/10.3390/chemosensors9100285 - 6 Oct 2021

Cited by 7 | Viewed by 3211

Abstract

Fluoride ion plays a pivotal role in a range of biological and chemical applications however excessive exposure can cause severe kidney and gastric problems. A simple and selective molecular sensor, 4,5-di(thien-2-yl)-2-(4-(1,2,2-triphenylvinyl)-phenyl)-1H-imidazole, DTITPE, has been synthesized for the detection of fluoride ions, with detection limits of 1.37 × 10⁻⁷ M and 2.67 × 10⁻¹³ M, determined by UV-vis. and fluorescence spectroscopy, respectively. The variation in the optical properties of the molecular sensor in the presence of fluoride ions was explained by an intermolecular charge transfer (ICT) process between the bis(thienyl) and tetraphenylethylene (TPE) moieties upon the formation of a N-H---F⁻ hydrogen bond of the imidazole proton. The sensing mechanism exhibited by DTITPE for fluoride ions was confirmed by ¹H NMR spectroscopic studies and density functional theory (DFT) calculations. Test strips coated with the molecular sensor can detect fluoride ions in THF, undergoing a color change from white to yellow, which can be observed with the naked eye, showcasing their potential real-world application. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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14 pages, 5044 KiB

Open AccessArticle

Potentiometric C₂H₄-Selective Detection on Solid-State Sensors Activated with Bifunctional Catalytic Nanoparticles

by Fidel Toldra-Reig and Jose Manuel Serra

Chemosensors 2021, 9(10), 274; https://doi.org/10.3390/chemosensors9100274 - 27 Sep 2021

Cited by 4 | Viewed by 2249

Abstract

This work presents a solid-state ionic-based device to selectively detect C₂H₄in car exhaust gases. The sensor consists of 8YSZ as the electrolyte and two electrodes: Fe_0.7Cr_1.3O₃/8YSZ and LSM/8YSZ. The main aim of this work is to optimize the catalytic behavior of the working electrode to C₂H₄and reduce cross-sensitivity toward CO and H₂O. Several catalyst nanoparticles were infiltrated to tailor C₂H₄ adsorption and electrochemical oxidation properties while diminishing adsorption and conversion of other gas components such as CO. The infiltrated metal catalysts were selected, taking into account both adsorption and redox properties. Infiltration of Ti or Al, followed by a second infiltration of Ni, enabled the selective detection of C₂H₄with low cross-sensitivity toward CO and H₂O in a moist gas environment. Further insight into potentiometric C₂H₄ sensing is achieved by electrochemical impedance analysis of the electrodes activated with bifunctional catalysts. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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12 pages, 3404 KiB

Open AccessArticle

Single Nanowire Gas Sensor Able to Distinguish Fish and Meat and Evaluate Their Degree of Freshness

by Matteo Tonezzer

Chemosensors 2021, 9(9), 249; https://doi.org/10.3390/chemosensors9090249 - 3 Sep 2021

Cited by 9 | Viewed by 2688

Abstract

A non-invasive, small, and fast device is needed for food freshness monitoring, as current techniques do not meet these criteria. In this study, a resistive sensor composed of a single semiconductor nanowire was used at different temperatures, combining the responses and processing them with multivariate statistical analysis techniques. The sensor, very sensitive to ammonia and total volatile basic nitrogen, proved to be able to distinguish samples of fish (marble trout, Salmo trutta marmoratus) and meat (pork, Sus scrofa domesticus), both stored at room temperature and 4 °C in the refrigerator. Once separated, the fish and meat samples were classified by the degree of freshness/degradation with two different classifiers. The sensor classified the samples (trout and pork) correctly in 95.2% of cases. The degree of freshness was correctly assessed in 90.5% of cases. Considering only the errors with repercussions (when a fresh sample was evaluated as degraded, or a degraded sample was evaluated as edible) the accuracy increased to 95.2%. Considering the size (less than a square millimeter) and the speed (less than a minute), this type of sensor could be used to monitor food production and distribution chains. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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Review

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22 pages, 4206 KiB

Open AccessReview

Atomistic Descriptions of Gas-Surface Interactions on Tin Dioxide

by Stefan Kucharski and Chris Blackman

Chemosensors 2021, 9(9), 270; https://doi.org/10.3390/chemosensors9090270 - 18 Sep 2021

Cited by 12 | Viewed by 2908

Abstract

Historically, in gas sensing literature, the focus on “mechanisms” has been on oxygen species chemisorbed (ionosorbed) from the ambient atmosphere, but what these species actually represent and the location of the adsorption site on the surface of the solid are typically not well described. Recent advances in computational modelling and experimental surface science provide insights on the likely mechanism by which oxygen and other species interact with the surface of SnO₂, providing insight into future directions for materials design and optimisation. This article reviews the proposed models of adsorption and reaction of oxygen on SnO₂, including a summary of conventional evidence for oxygen ionosorption and recent operando spectroscopy studies of the atomistic interactions on the surface. The analysis is extended to include common target and interfering reducing gases, such as CO and H₂, cross-interactions with H₂O vapour, and NO₂ as an example of an oxidising gas. We emphasise the importance of the surface oxygen vacancies as both the preferred adsorption site of many gases and in the self-doping mechanism of SnO₂. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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24 pages, 8930 KiB

Open AccessReview

Low-Dimensional Nanostructures Based on Cobalt Oxide (Co₃O₄) in Chemical-Gas Sensing

by Gayan W. C. Kumarage and Elisabetta Comini

Chemosensors 2021, 9(8), 197; https://doi.org/10.3390/chemosensors9080197 - 29 Jul 2021

Cited by 37 | Viewed by 4162

Abstract

Highly sensitive, stable, low production costs, together with easy maintenance and portability, sensors are ever most demanded nowadays for monitoring and quantification of hazardous chemicals/gases in the environment. The utilization of one dimensional (1D) metal oxide nano structured chemical/gas sensors for environmental monitoring is vastly investigated because of their superior surface to volume ratio, stability, and low production costs, to provide information on the presence of chemical species. Several outstanding attempts have been pursued investigating 1D nano structures of Co₃O₄ over the past decades as an active material for chemical analytes detection owing to its superior catalytic effect together with its excellent stability. This article reviews the state-of-the-art of growth and characterization of Co₃O₄ 1D nano structures and their functional characterization as chemical/gas sensors. Moreover, fundamental concepts and characteristic features, that enhance the key performances of chemical/gas sensors, are discussed. Finally, challenges and prospective for growth and fabrication of 1D Co₃O₄ chemical/gas sensors are discussed. Full article

(This article belongs to the Special Issue Gas Sensors: Simulation, Modeling, and Characterization)

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