Field-Effect Transistors for Gas Sensing

This chapter reviews gas-sensitive field-effect transistors (FETs) for gas sensing. Although various types of gas sensors have been reported, this review focuses on FET-based sensors such as catalytic-gate FETs, solid electrolyte-based FETs, suspended-gate FETs, and nanomaterial-based FETs. For recognition of analytes in the gas phase, the combination of cross-reactive gas sensor arrays with pattern recognition methods is promising. Cross-reactive sensor arrays consist of gas sensors that have broad and differential sensitivity. Signals from the cross-reactive sensor array are processed using pattern recognition methods. Reports of FET-based sensor arrays combined with pattern recognition methods are briefly reviewed

Wearable Nano-Based Gas Sensors for Environmental Monitoring and Encountered Challenges in Optimization

With a rising emphasis on public safety and quality of life, there is an urgent need to ensure optimal air quality, both indoors and outdoors. Detecting toxic gaseous compounds plays a pivotal role in shaping our sustainable future. This review aims to elucidate the advancements in smart wearable (nano)sensors for monitoring harmful gaseous pollutants, such as ammonia (NH3), nitric oxide (NO), nitrous oxide (N2O), nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), ozone (O3), hydrocarbons (CxHy), and hydrogen fluoride (HF). Differentiating this review from its predecessors, we shed light on the challenges faced in enhancing sensor performance and offer a deep dive into the evolution of sensing materials, wearable substrates, electrodes, and types of sensors. Noteworthy materials for robust detection systems encompass 2D nanostructures, carbon nanomaterials, conducting polymers, nanohybrids, and metal oxide semiconductors. A dedicated section dissects the significance of circuit integration, miniaturization, real-time sensing, repeatability, reusability, power efficiency, gas-sensitive material deposition, selectivity, sensitivity, stability, and response/recovery time, pinpointing gaps in the current knowledge and offering avenues for further research. To conclude, we provide insights and suggestions for the prospective trajectory of smart wearable nanosensors in addressing the extant challenges

Breath analysis of Volatile Organic Compounds for early-stage disease detection using nanomaterials

Είναι ευρέως αποδεκτό πως η διάγνωση μιας ασθένειας σε πρώιμο στάδιο είναι εξαιρετικής σημασίας, καθώς αυξάνει την πιθανότητα επιτυχούς θεραπείας, σε αντίθεση με την διάγνωση σε προχωρημένο στάδιο. Η μειωμένη συμμόρφωση των ασθενών προς τις υπάρχουσες διαγνωστικές μεθόδους, ωστόσο, παρεμποδίζει την έγκαιρη διάγνωση, καθιστώντας την ανάπτυξη μη-επεμβατικών διαγνωστικών μέσων επιτακτική ανάγκη. Η ανάλυση του εκπνεόμενου αέρα αποτελεί μια από τις πιο υποσχόμενες μη-επεμβατικές διαγνωστικές μεθόδους, προσελκύοντας το ερευνητικό ενδιαφέρον τα τελευταία χρόνια. Οι Πτητικές Οργανικές Ενώσεις που περιέχονται στον εκπνεόμενο αέρα θεωρούνται πιθανοί βιοδείκτες, εξαιρετικής σημασίας, για ένα πλήθος διαφορετικών ασθενειών. Η διαγνωστική ικανότητα διαφορετικών συνόλων πτητικών οργανικών ενώσεων έχει αναδειχθεί, τόσο με τη χρήση αναλυτικών τεχνικών όσο και – κυριότερα – με τη χρήση αισθητήρων αερίων. Η όλο και εντονότερη ανάπτυξη καινοτόμων νανοϋλικών, κατάλληλων για την δημιουργία αισθητήριων μέσων, επιτρέπει την ανάπτυξη αποτελεσματικότερων διαγνωστικών αισθητήρων, αποτελώντας, συνεπώς, ένα σημαντικό σύγχρονο ερευνητικό πεδίο. Η συγκεκριμένη εργασία στοχεύει, αρχικά, στην παρουσίαση των διαφόρων τύπων νανοϋλικών και αισθητήρων που μελετώνται για διαγνωστικές εφαρμογές. Εν συνεχεία – λαμβάνοντας υπόψιν την σημασία της συνετής και οργανωμένης επιλογής των αισθητήριων υλικών ενός αισθητήρα – παρουσιάζεται μια επισκόπηση των παραγόντων που επηρεάζουν την αλληλεπίδραση των πτητικών οργανικών ενώσεων με πολυμερικά υμένια – ένα κοινό συστατικό των αισθητήριων μέσων. Τέλος, προτείνεται μια σειρά πολυμερών, τα οποία θα μπορούσαν να χρησιμοποιηθούν για την δημιουργία χημικών αισθητήρων αντίστασης, βασισμένων σε μεταλλικά σωματίδια επικαλυμμένα με πολυμερικά υμένια, με στόχο την ανίχνευση εκπνεόμενων πτητικών οργανικών ενώσεων που έχουν χαρακτηριστεί επαναλαμβανόμενα ως πιθανοί βιοδείκτες για το Άσθμα, την Χρόνια Αποφρακτική Πνευμονοπάθεια, τον Καρκίνο του Πνεύμονα και τον Καρκίνο του Μαστού.Undoubtedly, early-stage disease diagnosis is of particular importance, increasing the chances for effective treatment, in comparison to advanced-disease stages. Lack of patient compliance for the existing diagnostic methods, however, limits prompt diagnosis, rendering the development of non-invasive diagnostic tools mandatory. One of the most promising non-invasive diagnostic methods that has attracted the research interest during the last years is breath analysis. Volatile Organic Compounds (VOCs) contained in the exhaled breath are considered as important potential biomarkers of various types of diseases. The diagnostic ability of VOC-patterns detection using analytical techniques and, especially, sensors, has been demonstrated. The progressive development of novel nanomaterials, suitable for sensing element creation, enhances the development of effective diagnostic sensors, comprising a major topic of current research. The current thesis aims, firstly, to present an overview of the various types of nanomaterials and sensors investigated for diagnostic sensors development. Further on, taking into consideration the importance of sensible sensing-material selection, the parameters affecting the interactions of VOCs with polymers – a common component of sensing elements – are summarized. Last but not least, a series of polymers that could potentially detect repeatedly identified VOCs as potential biomarkers of asthma, COPD, lung and breast cancer, using a polymer coated-MNSs based chemiresistor are proposed

Overview of Gas Sensors Focusing on Chemoresistive Ones for Cancer Detection

The necessity of detecting and recognizing gases is crucial in many research and application fields, boosting, in the last years, their continuously evolving technology. The basic detection principle of gas sensors relies on the conversion of gas concentration changes into a readable signal that can be analyzed to calibrate sensors to detect specific gases or mixtures. The large variety of gas sensor types is here examined in detail, along with an accurate description of their fundamental characteristics and functioning principles, classified based on their working mechanisms (electrochemical, resonant, optical, chemoresistive, capacitive, and catalytic). This review is particularly focused on chemoresistive sensors, whose electrical resistance changes because of chemical reactions between the gas and the sensor surface, and, in particular, we focus on the ones developed by us and their applications in the medical field as an example of the technological transfer of this technology to medicine. Nowadays, chemoresistive sensors are, in fact, strong candidates for the implementation of devices for the screening and monitoring of tumors (the second worldwide cause of death, with ~9 million deaths) and other pathologies, with promising future perspectives that are briefly discussed as well

Synthesis and gas sensing properties of inorganic semiconducting, p-n heterojunction nanomaterials

En aquesta tesis utilitzant principalment Aerosol Assited Chemical Vapor Deposition, AACVD, com a metodologia de síntesis d'òxid de tungstè nanoestructurat s'han fabricat diferents sensors de gasos. Per tal d'estudiar la millora en la selectivitat i la sensibilitat dels sensors de gasos basats en òxid de tungstè aquest s'han decorat, via AACVD, amb nanopartícules d'altres òxids metàl·lics per a crear heterojuncions per tal d'obtenir un increment en la sensibilitat electrònica, les propietats químiques del material o bé ambdues. En particular, s'han treballat en diferents sensors de nanofils d'òxid de tungstè decorats amb nanopartícules d'òxid de níquel, òxid de cobalt i òxid d'iridi resultant en sensors amb un gran increment de resposta i selectivitat cap al sulfur d'hidrogen, per a l'amoníac i per a l'òxid de nitrogen respectivament a concentracions traça. A més a més, s'han estudiat els mecanismes de reacció que tenen lloc entre les espècies d'oxigen adsorbides a la superfície del sensor quan interactua amb un gas. I també s'ha treballat en intentar controlar el potencial de superfície de les capes nanoestructurades per tal de controlar la deriva en la senyal al llarg del temps, quan el sensor està operant, a través d'un control de temperatura.En esta tesis utilizando principalmente Aerosol Assited Chemical Vapor Deposition, AACVD, como metodología de síntesis de óxido de tungsteno nanoestructurado se han fabricado diferentes sensores de gases. Para estudiar la mejora en la selectividad y la sensibilidad de los sensores de gases basados en óxido de tungsteno estos se han decorado, vía AACVD, con nanopartículas de otros óxidos metálicos para crear heterouniones para obtener un incremento en la sensibilidad electrónica, las propiedades químicas del material o bien ambas. En particular, se han trabajado en diferentes sensores de nanohilos de óxido de tungsteno decorados con nanopartículas de óxido de níquel, óxido de cobalto y óxido de iridio resultante en sensores con un gran incremento de respuesta y selectividad hacia el sulfuro de hidrógeno, para el amoníaco y para el óxido de nitrógeno respectivamente a concentraciones traza. Además, se han estudiado los mecanismos de reacción que tienen lugar entre las especies de oxígeno adsorbidas en la superficie del sensor cuando interactúa con un gas. Y también se ha trabajado en intentar controlar el potencial de superficie de las capas nanoestructuradas para controlar la deriva en la señal a lo largo del tiempo, cuando el sensor está trabajando, a través de un control de temperatura.In this thesis, using mainly Aerosol Assited Chemical Vapor Deposition, AACVD, as a synthesis methodology for nanostructured tungsten oxide, different gas sensors have been manufactured. To study the improvement in the selectivity and sensitivity of gas sensors based on tungsten oxide, they have been decorated, via AACVD, with nanoparticles of other metal oxides to create heterojunctions to obtain an increase in electronic sensitivity, in the chemical properties of the material or at the same time in both. Particularly, we have worked on different tungsten oxide nanowire sensors decorated with nanoparticles of nickel oxide, cobalt oxide and iridium oxide resulting in sensors with a large increase in response and selectivity towards hydrogen sulfide, for ammonia. and for nitrogen oxide respectively at trace concentrations. In addition, the reaction mechanisms that take place between oxygen species adsorbed on the sensor surface when it interacts with a gas have been also studied. Furthermore, efforts have been put on trying to control the surface potential of the nanostructured layers to control the drift in the signal over time, when operating the sensors, through temperature control

Graphene Based Sensors for Air Quality Monitoring - Preliminary Development Evaluation

Indoor air pollution can induce adverse health effects on building occupants and pose a significant role in health worldwide. To avoid such effects, it is extremely important to monitor and control common indoor pollutants such as CO2, VOCs and relative humidity. Therefore, this work focuses on recent advances in the field of graphene-based gas sensors, emphasizing the use of modified graphene that broadly expands the range of nanomaterials sensors. Graphene films were grown on copper by chemical vapor deposition (CVD) and transferred to arbitrary substrates. After synthesis, the samples were functionalized with Al2O3 by ALD and characterized by a large set of experimental techniques such as XPS, Raman and SEM. The results demonstrated that graphene was successfully synthesized and transferred to SiO2, glass and polymer. As a proof-of-concept, ALD of Al2O3 was performed on the graphene surface to produce a graphene/metal oxide nanostructure towards the development of nanocomposites for gas sensing. From this perspective, a laboratory prototype device based in measuring the electrical properties of the graphene sample as a function of the gas absorption is under development

Electronic nose for analysis of volatile organic compounds in air and exhaled breath.

Exhaled breath is a complex mixture containing numerous volatile organic compounds (VOCs) at trace levels (ppb to ppt) including hydrocarbons, alcohols, ketones, aldehydes, esters and other non-volatile compounds. Different patterns of VOCs have been correlated with various diseases. The concentration levels of VOCs in exhaled breath depend on an individual subject’s health status. Therefore, breath analysis has great potential for clinical diagnostics, monitoring therapeutic progress and drug metabolic products. Even though up to 3000 compounds may be detected in breath, the matrix of exhaled breath is less complex than that of blood or other body fluids. Breath analysis can be performed on people irrespective of age, gender, lifestyle, or other confounding factors. Breath gas concentration can be related to VOC concentrations in blood via mathematical modeling; for example, as in blood alcohol testing. Since exhaled breath samples are easy to collect and online instruments are commercially available, VOC analysis in exhaled breath appears to be a promising tool for noninvasive detection and monitoring of diseases. Breath analysis has been very successful in identifying cancer, diabetes and other diseases by using a chemiresistor sensor array to detect biomarkers. The objective of this research project is to develop sensor arrays ― or so-called electronic nose ― for analysis of VOCs in air and exhaled breath. In this dissertation, we have investigated both commercial and synthesized thiol functionalized gold nanoparticles (AuNPs) as sensing materials for analysis of VOCs in air and exhaled breath. The advantages of these sensors include very high sensitivity, selectivity for detection of target analytes and operation at ambient temperature. The synthesis and material characterization of new thiols and AuNPs for increasing sensitivity and selectivity have been studied. Selected commercial thiols and in-house synthesized new functional thiols have been used to modify AuNP-based sensors for detection of VOCs in air and exhaled breath. The interdigitated electrodes (IDE) used for the sensors were fabricated by microelectromechanical systems (MEMS) microfabrication technologies. The sensor arrays were characterized by measuring the resistance difference from vacuum and different spiked analyte concentrations in air and breath samples. Air samples and breath samples were collected using Tedlar bags, and analyzed using the thiol functionalized AuNP sensors. The analysis of air samples provides a reference for analysis of exhaled breath samples. The sensors have demonstrated a low detection limit of 0.1 ppbv of acetone and ethanol in dry air and exhaled breath. The concentrations of acetone in air and exhaled breath were determined by a silicon microreactor approach. The measurements of acetone by the microreactor approach were correlated with the sensor signals. The intellectual thrust of this research is the rational design of an electronic nose for analysis of VOCs in exhaled breath, which offers a new frontier in medical diagnostics because of its non-invasive and inexpensive characteristics

Nano-Bio Hybrid Electronic Sensors for Chemical Detection and Disease Diagnostics

The need to detect low concentrations of chemical or biological targets is ubiquitous in environmental monitoring and biomedical applications. The goal of this work was to address challenges in this arena by combining nanomaterials grown via scalable techniques with chemical receptors optimized for the detection problem at hand. Advances were made in the CVD growth of graphene, carbon nanotubes and molybdenum disulfide. Field effect transistors using these materials as the channel were fabricated using methods designed to avoid contamination of the nanomaterial surfaces. These devices were used to read out electronic signatures of binding events of molecular targets in both vapor and solution phases. Single-stranded DNA functionalized graphene and carbon nanotubes were shown to be versatile receptors for a wide variety of volatile molecular targets, with characteristic responses that depended on the DNA sequence and the identity of the target molecule, observable down to part-per-billion concentrations. This technology was applied to increasingly difficult detection challenges, culminating in a study of blood plasma samples from patients with ovarian cancer. By working with large arrays of devices and studying the devices\u27 responses to pooled plasma samples and plasma samples from 24 individuals, sufficient data was collected to identify statistically robust patterns that allow samples to be classified as coming from individuals who are healthy or have either benign or malignant ovarian tumors. Solution-phase detection experiments focused on the design of surface linkers and specific receptors for medically relevant molecular targets. A non-covalent linker was used to attach a known glucose receptor to carbon nanotubes and the resulting hybrid was shown to be sensitive to glucose at the low concentrations found in saliva, opening up a potential pathway to glucose monitoring without the need for drawing blood. In separate experiments, molybdenum disulfide transistors were functionalized with a re-engineered variant of a μ-opiod receptor, a cell membrane protein that binds opiods and regulates pain and reward signaling in the body. The resulting devices were shown to bind opiods with affinities that agree with measurements in the native state. This result could enable not only an advanced opiod sensor but moreover could be generalized into a solid-state drug testing platform, allowing the interactions of novel pharmaceuticals and their target proteins to be read out electronically. Such a system could have high throughput due to the quick measurement, scalable device fabrication and high sensitivity of the molybdenum disulfide transistor

Sensor Technology for Opening New Pathways in Diagnosis and Therapeutics of Breast, Lung, Colorectal and Prostate Cancer

This study analyzes the interaction between sensor research and technology and different types of cancer (breast, lung, colorectal, and prostate) with the goal of detecting new directions for improving diagnosis and therapeutics in medicine. This study develops an approach to computational scientometrics based on data from the Web of Science from the 1991 to 2021 period. The results of this analysis show the vital role of biosensors and electrochemical biosensors applied in breast cancer, lung cancer, and prostate cancer research. Instead, scientific research of optical sensors is developing main technological trajectories in breast, prostate, and colorectal cancer for improving diagnostics. Finally, oxygen sensor research has a main technological development in breast and lung cancer for new applications in breath analysis directed to treatment processes. Preliminary results presented here clearly illustrate the evolutionary paths of sensor research and technologies that have great potential for developing incremental and radical innovations in cancer diagnosis and therapies. These conclusions are, of course, tentative. There is a need for much more detailed research based on other aspects and factors for detecting stable technological trajectories that can foster the technology transfer of new sensor in cancer research for improving diagnosis and therapeutics, reducing, whenever possible, world-wide mortality of cancer in society.JEL Classification: I10, O30, O31, O32; O33. Doi: 10.28991/HIJ-2022-03-03-010 Full Text: PD

DNA-templated nanowires for sensing volatile organic compounds

PhD ThesisThe fabrication of gas sensors with semi-conducting nanowires has attracted considerable interest in recent times because of their potential of selective and fast detection of low quantities of gaseous analyte when incorporated into miniature and low-power consumer electronics. DNA templating is a relatively new process for fabrication of nanowires at room temperature without the requirement for vacuum technology. This thesis describes the synthesis, characterization and gas sensing application of DNA templated metal sulfides and carbon nanotube nanowires. DNA templated CdS, CdZnS2 and ZnS were synthesized in solution to form smooth and continuous nanowires.The reaction involves initial coordination of the metal ion(s) with DNA and subsequent co-precipitation with sulfide ions upon addition of Na2S.The nanowires were deposited on the substrate via molecular combing to form a wellaligned network for electrical characterisation and gas sensing experiments. The structure, chemical composition and morphology of the nanowires were characterised by atomic force microscopy (AFM), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, photoluminescence (PL), fluorescence microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. These techniques showed that the metal sulfides interact with the DNA template to form microcrystalline nanowires of typical diameter < 10 nm and controllable Cd:Zn ratio. The current-voltage (I-V) properties as a function of temperature were measured using micro-band electrodes on a probe station, Impedance spectroscopy and current transients were used to estimate contact resistances. The nanowires showed weak conductivity with I-V curves typical of metalsemiconductor-metal systems and described by the space charge limited conduction model. The temperature dependent properties of the nanowires showed simple Arrhenius behaviour. The room temperature sensing properties of the nanowires to volatile organic compounds (VOCs) such as ethanol, acetone, chloroform and hexane were also determined. They demonstrated good and reversible sensing response to the VOCs but with a higher sensitivity towards ethanol. The result also suggests that the room temperature sensing mechanism of the VOCs molecules on CdS/DNA, ZnS/DNA and CdZnS2/DNA nanowire sensor is essentially driven by their direct adsorption on the surface and interaction with charges in the nanowires