Solid-state Chemical Sensors Research Articles

AC Excitation to Mitigate Drift in AlGaN/GaN HEMT-Based Sensors

AlGaN/GaN high electron mobility transistor (HEMT) based sensors hold promise as small solid-state physical and chemical sensors because they can operate without a reference electrode and can be integrated into miniaturized sensor arrays. However, over extended time periods, low frequency noise causes anomalous variations (drift) in sensor signal, especially in liquid environments. These effects occur despite electromagnetic interference mitigation. To understand the low frequency noise, 1/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> noise measurements between 0.1 and 100 kHz were undertaken, in both air and water, under constant pH and normal laboratory pressure conditions. The 1/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">γ</sup> noise for the device in water was larger in magnitude than in air, and estimates for the γ-parameter in air and water were approximately 1 and 1.5, respectively. The corner frequency was observed between 100 and 1000 Hz. Based on this analysis, AC excitation at 1 kHz was applied to the conduction channel to compare the sensor stability in de-ionized water with DC operation. In this controlled test, introduction of AC excitation resulted in a strong correlation of sensor signal with the ambient temperature variations over nearly 90 hours of testing (effectively acting as a temperature sensor with a high degree of stability) while operation in DC mode resulted in largely no correlation with temperature. This indicates that AC excitation above the corner frequency is a potentially effective method to mitigate long-term sensor instability, a critical limitation for any AlGaN/GaN transistor-based physical or chemical sensors in aqueous environments.

A sensitive detection approach for Cu(II) ions in water samples using a solid-state chemical sensor

ABSTRACT We describe the creation of a solid-state optical sensor that is quick to respond, sensitive, and reliable for detecting and determining Cu(II) ions in both natural and wastewater sources. The solid-state template was prepared with mesoporous silica nanospheres of capacious porosity, high surface area, and uniform surface morphology. N,N’-bis(3-carboxysalcylidene)-4-chloro-1,2-phenylenediamine (CSCPD), a chromoionophoric probe with exclusive ion-selectivity and sensitivity for Cu(II), is created for use in naked-eye colorimetric detection. The mesoporous silica nanospheres (MSNs) template displayed several diffusible sites for the uniform anchoring of the CSCPD probe molecules, which serve as a colorimetric ion sensor for the naked eye. The surface profile and structure of the MSNs and the CSCPD sensor materials are studied using BET/BJH, XPS, FESEM, p-XRD, and HR-TEM analysis. With various concentrations of Cu(II), the CSCPD probe-anchored MSNs material reciprocates a vivid visual colour shift from an initial pale yellow colour to green with a reaction period of around one minute. In addition, the MSNs are simply covered with probe molecules as part of the sensor production process. The certified limits of detection for Cu(II) ions for the proposed CSCPD sensor is 1.57 ppb (2.48 × 10−8 M). The suggested CSCPD sensor is dual-functional in that it may be used as a concentrator to recover ultra-trace quantities of Cu(II) ions as well as an effective ion-sensing device.

M-cymene and m-xylene adsorption studies on hex-star arsenene nanosheets – a DFT investigation

The monitoring of toxic vapours such as M-cymene and m-xylene from industries is a significant task using a solid-state chemical sensor. We report the structurally stable hex-star arsenene sheets (hex-star AsNS) as a base material to perceive the presence of M-cymene and m-xylene molecules. Initially, we examined the formation energy of hex-star AsNS and ensured the geometric stability. Besides, hex-star AsNS possesses an energy band gap of 1.033 eV indicating the semiconductor state. We explored the changes in the band structure and PDOS (projected density of states) spectrum of hex-star AsNS upon adsorption of M-cymene and m-xylene molecules. Also, concerning charge transfer and electron density difference studies, the electronic properties of hex-star AsNS are reconnoitered. The adsorption energy upon M-cymene and m-xylene adsorption show the physisorption of target molecules on hex-star AsNS. The outcome reveals the hex-star AsNS as an emerging material for the detection of M-cymene and m-xylene molecules.

Benefits of virtual sensors for air quality monitoring in humid conditions

The gas sensing mechanisms, response, and behaviour of a real and a virtual solid-state chemical gas sensor operating either in static or in dynamic mode have been compared. The analysis was done by exposing simultaneously both sensors to different concentrations of various volatile organic compounds diluted in dry, as well as humid, synthetic air. The results revealed similar responses and behaviours for both types of measurement modes when the sensors were exposed towards single gas compounds, but a sensitivity enhancement in measurements comprising mixtures of gases when the sensors were operated in dynamic mode. The method used is able to overcome surface saturation problems and is beneficial for applications where mixtures of gases diluted in relative humidity are present.

Explosive vapor detection using novel graphdiyne nanoribbons—a first-principles investigation

We investigated the capability of graphdiyne nanoribbon (GdNR) to detect the existence of explosive vapors like hexogen or cyclonite, hexamethylene triperoxide diamine (HMTD), and 2,4,6-trinitrotoluene (TNT) using ATK-VNL package. In order to determine the sensing response of GdNR towards these explosive vapors, the geometric firmness of the material is first verified with the assistance of cohesive energy. Then, electronic characteristics like the projected density of states (PDOS) spectrum, band structure, and electron density are examined for both isolated and explosive vapor adsorbed GdNR. Further, adsorption attributes like average energy gap variation, enthalpy adsorption, adsorption energy, and Bader charge transfer are explored for explosive vapor adsorbed GdNR. Moreover, there is a need for rapid detection of explosive vapors using solid-state chemical sensors. The scrutinization of these attributes affirms the employment of GdNR as a chief material in a chemical nanosensor to perceive the availability of the mentioned explosive vapors.

Facile synthesis of high-stable and monodisperse Fe3O4/carbon flake-like nanocomposites and their excellent gas sensing properties

In this paper, flake-like Fe3O4/carbon (Fe3O4/C) nanocomposites were synthesized via a facile molten-salt method using ferric-oleate as precursor and sodium sulfate as template. Transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM) results showed that highly stable and monodisperse Fe3O4 nanocrystals were firmly embedded in flake-like carbon carriers. As a active layer in solid-state resistive chemical sensor, the gas sensing properties of the sensing layer in controlled atmospheres such as ethyl acetate, acetic acid, ethanol and acetone, at different concentrations and working temperatures were systematically tested. The gas sensing results revealed that the Fe3O4/C nanocomposites sensors exhibited high sensitivity, short recovery time to the above vapors. The excellent gas-sensing properties of the prepared nanostructures are attributed to the surface structure of Fe3O4/C nanocomposites. The reason is that the carbon film can inhibit the agglomeration of Fe3O4 nanoparticles, and maintain the shape and size of Fe3O4 nanoparticles when working, thus maintaining the good gas sensing properties. This study provides a new idea for the design of carbon film supported nanoparticle materials, and is expected to be widely used in other applications in the future.

Performance analysis of solid-state nanopore chemical sensor

The performance of solid-state nanopore chemical sensor is analyzed in this paper with respect to sensitivity and detection limit. A simplified analytical model is derived to provide better understanding on the conductivity change of nanopores with respect to the radius, ionic concentration, and surface charge density. The paper shows that the sensitivity and limit of detection can be optimized by working in a background solution of low ionic concentration solution (in the range of mM) and high mobility cation, with an appropriate high input voltage. The current noise is analyzed in the form of current power spectra density, which act as a solid support for understanding the noise behavior and detection resolution analysis.

Relevance of the automated systems of environmental monitoring in the implementation of the best available technologies

The current state of the environment causes increasing concerns. At the same time, the tasks of economic development require expansion of industrial production, which in turn increases the burden on the environment. The solution to this contradiction is seen in using the best available technologies (BAT) as an economically more effective alternative to “green” technologies. Since the best available technologies do not involve the abandonment of the use of hazardous process substances, environmental monitoring systems that show the level of environmental contamination from them should be the most important concomitant element of these technologies. Solid-state chemical sensors can be used as the basis of such systems. To achieve high technical efficiency, the systems must be automatic or at least automated that will increase the level of public confidence in their work.

Nanostructured Fe2O3 Processing via Water‐Assisted ALD and Low‐Temperature CVD from a Versatile Iron Ketoiminate Precursor

Vapor phase deposited iron oxide nanostructures are promising for fabrication of solid state chemical sensors, photoelectrodes for solar water splitting, batteries, and logic devices. The deposition of iron oxide via chemical vapor deposition (CVD) or atomic layer deposition (ALD) under mild conditions necessitates a precursor that comprises good volatility, stability, and reactivity. Here, a versatile iron precursor, namely [bis(N‐isopropylketoiminate) iron(II)], which possesses ideal characteristics both for low‐temperature CVD and water‐assisted ALD processes, is reported. The films are thoroughly investigated toward phase, composition, and morphology. As‐deposited ALD grown Fe2O3 layers are amorphous, while the CVD process in the presence of oxygen leads to polycrystalline hematite layers. The nanostructured iron oxide grown via CVD consists of nanoplatelets that are appealing for photoelectrochemical applications. Preliminary tests of the photoelectrocatalytic activity of CVD‐grown Fe2O3 layers show photocurrent densities up to 0.3 mA cm−2 at 1.2 V versus reversible hydrogen electrode (RHE) and 1.2 mA cm−2 at 1.6 V versus RHE under simulated sunlight (1 sun). Surface modification by cobalt oxyhydroxide (Co‐Pi) co‐catalyst is found to have a highly beneficial effect on photocurrent, leading to maximum monochromatic quantum efficiencies of 10% at 400 nm and 4% at 500 nm at 1.5 V versus RHE.

Nanopore-enabled electrode arrays and ensembles

This review (with 116 refs.) addresses recent developments in nanoelectrode arrays and ensembles with particular attention to nanopore-enabled arrays and ensembles. Nanoelectrode-based arrays exhibit unique mass transport and ion transfer properties, which can be exploited for electroanalytical measurements with enhanced figures-of-merit with respect to microscale and larger components. Following an introduction into the topic, we cover (a) methods for fabrication of solid-state nanopore electrodes, (b) chemical and biochemical sensors, (c) nanochannel arrays with embedded nanoelectrodes; (d) recessed nanodisk electrode arrays; (e) redox cycling in nanopore electrode arrays, (f) finally discuss novel nanoarrays for electrochemistry, and then give a future outlook. A wide variety of nanoelectrode array-based chemical and biochemical sensors properties are discussed in addition to faradaic, ion transfer and spectroelectrochemical applications.

Application of Photocured Polymer Ion Selective Membranes for Solid-State Chemical Sensors

Application of conducting polymers with additional functional groups for a solid contact formation and photocurable membranes as sensitive elements of solid-state chemical sensors is discussed. Problems associated with application of UV-curable polymers for sensors are analyzed. A method of sensor fabrication using copolymerized conductive layer and sensitive membrane is presented and the proof of concept is confirmed by two examples of solid-contact electrodes for Ca ions and pH.

ChemInform Abstract: SnO2: A Comprehensive Review on Structures and Gas Sensors

AbstractReview: 886 refs.

Pt/Metal Oxide Micro-Nanostructures for Chemical-Electrical Signal Transduction

Investigation of heterogeneous catalysis using bifunctional systems of nanodispersed Pt on porous oxide structures is important for a broad range of applications including photocatalysis, fuel cells, solid state chemical sensors, and others. Active transducers exhibit great potential through their ability to convert surface-released chemical energy into electrical signal. We report on a class of nanocomposite mesoporous systems that generate this electrical signal when subjected to catalytic oxyhydrogen reactions of their surface; these systems include, but are not limited to, mesoporous TiO2 decorated with electrically continuous arrays (meshes) of Pt nanoparticles. It has been proposed that the proton spillover hypothesis of the electromotive force in the mesoporous chemical-electrical transducer nanostructure leads to a multi-modal nature of the “chemicurrent” - non-thermal electrical signals related to hot electron and e-h pair generation. Structural and surface morphology play a pivotal role in the generation, transport, and recombination of electrical charge in these bifunctional catalytic systems. In this presentation, we discuss plasma electrolytic oxidation procedures that allow for the further optimization of mesoporous nanocomposite structures by controlling parameters such as pore density within the samples.

ChemInform Abstract: Recent Advances of Doping of SnO2 Nanocrystals for Their Potential Applications

AbstractReview: 88 refs.

Dispersible composites of exfoliated graphite and polyaniline with improved electrochemical behaviour for solid-state chemical sensor applications

The PANI–graphene/graphite composites show improved pH stability and electrochemical behaviour in aqueous electrolyte solutions at pH ≤ 8.

Improved charging/discharging behavior of electropolymerized nanostructured composite films of polyaniline and electrochemically reduced graphene oxide

In this work, a simple electrochemical reduction procedure has been applied to nanostructured composite films of polyaniline (PANI) and graphene oxide (GO) having a globular surface morphology with the grain size of 50nm. The reduction converts GO to reduced GO (rGO) which improves the electroactivity of the PANI composite films with 30%. Cyclic voltammetry confirmed the reduction of GO to rGO whereas electrochemical impedance spectroscopy showed that the rGO network increases the redox capacitance of the composite films with 15% to 77mFcm−2. In a three-electrode cell, the anodic charge of the PANI film containing GO increased with 18.7% during the potential cycling stability test for 10,000 cycles between −0.2 and 0.5V, indicating that the film had a good stability against degradation. This composite film type still maintained a high capacitance of 15mFcm−2 in a symmetric two-electrode cell after 10,000 potential cycles between 0 and 0.4V. The electrochemically prepared PANI composite films reported here are aimed to be used in capacitor applications where it is crucial to deposit thin PANI layers on well-defined small surfaces where other polymerization or deposition techniques cannot be used and in solid-state chemical sensors as ion-to-electron transducer interfaces.

Recent Advances of Doping of SnO2 Nanocrystals for Their Potential Applications

SnO2 nanocrystal is a novel wide band gap n-type semiconductor which exhibits outstanding electrical, optical and electrochemical properties that can be exploited for solar cells, catalytic support materials, transparent electrodes and solid-state chemical sensors applications. The main focus of this article is to address the impacts of doping on the various properties of SnO2 nanocrystals including optical, electrical, photocatalytic and gas sensing. Recently, emphasis is given on metal ion doped SnO2 nanocrystals to enhance the electrical and optical properties. Metal ion doped SnO2 nanocrystals are found to be potential candidates for gas-sensing devices. We will begin with the description of general synthetic methodologies for designing doped SnO2 nanostructure materials. Interesting findings are that the application-based properties such as photocatalytic and gas sensing are increased manifold after doping of SnO2 nanocrystals. Finally, a tentative outlook on future developments of this research field is given.

Thick film screen printed environmental and chemical sensor array reference electrodes suitable for subterranean and subaqueous deployments

PurposeThe purpose of this paper is to report thick film environmental and chemical sensor arrays designed for deployment in both subterranean and submerged aqueous applications.Design/methodology/approachVarious choices of materials for reference electrodes employed in these different applications have been evaluated and the responses of the different sensor types are compared and discussed.FindingsResults indicate that the choice of binder materials is critical to the production of sensors capable of medium term deployment (e.g. several days) as the binders not only affect the tradeoff between hydration time and drift but also have a significant bearing on device sensitivity and stability. Sensor calibration is shown to remain an issue with long‐term deployments (e.g. several weeks) but this can be ameliorated in the medium term with the use of novel device fabrication and packaging techniques.Originality/valueThe reported results indicate that is possible through careful choice of materials and fabrication methods to achieve near stable thick film reference electrodes that are suitable for use in solid state chemical sensors in a variety of different application areas.

Improved gas sensing performances in SPR sensors by transducers activation

In this paper, among all transduction methodologies reported in the field of solid state chemical sensors, the attention has been focused onto the optical sensing characterization by using surface plasmon resonance (SPR) technique and its evolution towards active plasmonics. Activation of the transducer by application of an oscillating magnetic field in a transversal configuration is demonstrated to improve the gas sensing performance of classical SPR sensors. To this purpose a new transducer, composed of metallic and magnetic materials and a proper sensing layer have been chosen. TiO2 sensing layers have been prepared by two different experimental routes and their optical and morphological features investigated and correlated with their sensing performances. A comparison between classical SPR technique and a new sensing probe based onto magneto-plasmonic effect in resonance condition has been reported. Improved gas sensing performance in terms of sensitivity has been demonstrated in the presence of different alcohol vapours concentration mixed in dry air.

ChemInform Abstract: Vacuum Technology Applied to Solid State Chemical Sensors, Processing, Characterization and Applications

AbstractReview: 31 refs.