Chemical sensors

Owing to the importance of explosive detection for the security of land and the environment, the exploration of new methodologies for sensing electron-deficient nitroaromatics explosives (NAEs) is urgently imperative. In this work, we firstly reported a colorimetric sensor for visual detection of 2,4,6-trinitrotoluene (TNT) based on Cysteamine capped-CdSe quantum dots (QDs) decorated graphene-chitosan xerogel (GSXS), which is shown to have high signal-to-background ratio. Meisenheimer complex formation, which is a well-known sensing mechanism, is characterized by steady state and time resolved spectroscopy supported by Density-Functional-Theory (DFT). Upon Green Fluorescent Protein (GFP) illumination, this stable Meisenheimer complex actively suppresses the attributed fluorescence of QD-GSXS and thus providing a novel path for chemical sensing applications. Under optimized conditions, the sensor displayed a wide linear range from 0.0 to 311.4 μ M with a limit of detection 9.7 μ M. T...

This paper reports the study of data quality of Cairsens NO2 environmental sensors. In order to evaluate sensors performances, the investigation was performed through: a prospective follow-up of short-term and long terms drifts, the evaluation of the effects of environmental conditions upon sensors measurements as well as the evaluation of the ozone-filter lifetime. In this purpose, a dedicated test bench has been developed to expose sensors to a fixed concentration of ozone while recording sensors response.

The health diagnosis of agricultural structures is critical to detecting damages such as cracks in concrete, corrosion, spalling, and delamination. Agricultural structures are susceptible to environmental degradation due to frequent exposure to water, organic effluent, farm chemicals, structural loading, and unloading. Various sensors have been employed for accurate and real-time monitoring of agricultural building structures, including electrochemical, ultrasonic, fiber-optic, piezoelectric, wireless, fiber Bragg grating sensors, and self-sensing concrete. The cost–benefits of each type of sensor and utility in a farm environment are explored in the review. Current literature suggests that the functionality of sensors has improved with progress in technology. Notable improvements made with the progress in technology include better accuracy of the measurements, reduction of signal-to-noise ratio, and transmission speed, and the deployment of machine learning, deep learning, and arti...

pH-sensing materials and configurations are rapidly evolving toward exciting new applications, especially those in biomedical applications. In this review, we highlight rapid progress in electrochemical pH sensors over the past decade (2008− 2018) with an emphasis on key considerations, such as materials selection, system configurations, and testing protocols. In addition to recent progress in optical pH sensors, our main focus in this review is on electromechanical pH sensors due to their significant advances, especially in biomedical applications. We summarize developments of electrochemical pH sensors that by virtue of their optimized material chemistries (from metal oxides to polymers) and geometrical features (from thin films to quantum dots) enable their adoption in biomedical applications. We further present an overview of necessary sensing standards and protocols. Standards ensure the establishment of consistent protocols, facilitating collective understanding of results and building on the current state. Furthermore, they enable objective benchmarking of various pH-sensing reports, materials, and systems, which is critical for the overall progression and development of the field. Additionally, we list critical issues in recent literary reporting and suggest various methods for objective benchmarking. pH regulation in the human body and state-of-the-art pH sensors (from ex vivo to in vivo) are compared for suitability in biomedical applications. We conclude our review by (i) identifying challenges that need to be overcome in electrochemical pH sensing and (ii) providing an outlook on future research along with insights, in which the integration of various pH sensors with advanced electronics can provide a new platform for the development of novel technologies for disease diagnostics and prevention. CONTENTS

Surface Acoustic Waves (SAWs) are elastic waves travelling along the surface of solid piezoelectric materials
with  amplitude  that  decays  exponentially  with  depth.  Using  an  Interdigital  Transducer  (IDT),  these  waves  can  be
demonstrated and reproduced in the laboratory in devices called SAW devices. Such devices find many applications as
delay  lines,  filters,  resonators  and  sensors.  The  present  paper  provides  a  snapshot  review  and  a  description  of  the
function,  operation  and  latest  technical  advancements  seen  in  SAW  sensors  over  the  period  from1997-2015.  SAW
Sensors  using  different  design  and  operating  principles  have  been  reported  in  this  paper.  Compared  with  other
currently  available  types  of  sensors,  the  SAW  –  based  sensors  have  many  advantages  like:  high  sensitivity,  quick
response time, easy predictability and good stability.

A new type of fluorescent chemosensor based on tethered hexa-borondipyrromethene cyclotriphosphazene platform (HBTC) linked via triazole groups was designed and synthesized. Its sensing behavior toward metal ions was investigated by ultraviolet-visible and fluorescence spectros-copies. Addition of a Fe 2+ ion to a tetrahydrofuran solution of HBTC gave a visual color change as well as a significantly quenched fluorescence emission, while other tested 19 metal ions induced no color or spectral changes. This compound was found to be highly selective and sensitive for Fe 2+ with a low limit of detection (2.03 μM) which is, to the best of our knowledge, the superior than the previously studied chemosensors for Fe 2+ .

A new rhodamine-derived Schiff base RH was synthesized and its sensing behavior toward various metal ions was investigated by UV–vis and fluorescence spectroscopic techniques. The sensor exhibited highly selective and sensitive colorimetric response to Cu 2+ and Al 3+ , and " off–on " fluorescence response toward Fe 3+ in semi-aqueous media. The spectral changes obtained are large enough in the visible region of the spectrum and thus enable naked-eye detection. Experimentally proved that the formation of RH–Al 3+ complex is fully reversible and can sense to AcO − /F − via break the complex. The results revealed that the sensor offers the sequential detection of Al 3+ and AcO − /F − .

tA new azo compound, 1-(2-pyridylazo)-2-naphthol, has been prepared and characterized. The synthe-sized compound shows a very high affinity for aluminium. The complexation reaction of aluminiumhas been explored by Colorimetry, FT-IR,1H NMR, HRMS and fluorescence spectroscopy. The detectionlimit has been found to be 1.81 × 10−8M estimated by the titration method. The turn-on fluorescencebehaviour of aluminium interaction with ligand has been found to be so fast (<5 s) that it can be used forits qualitative as well as quantitative estimation.

A compact model of an ion-sensitive floating gate FET (ISFGFET) is presented. Unlike in the conventional ISFET, the ISFGFET has a dual gate structure, a sensing gate and a control gate. With the interplay between the control gate and the reference electrode the charging of the fluidic part of the sensor can be controlled and the sensing surface can be programmed. We present an intuitive macromodel with SPICE implementation and discuss the fluidic gating, sensitivity, chemical and electrical tuning of the ionic screening layer as well as the methods to combat the limitations such as the dielectric breakdown of the sensing oxide as well as the design trade-offs of the sensor. Additionally the model allows the integration of this new type of chemical sensor to the CMOS design flow. The proposed model relies on experimentally verified site-binding theory and double layer capacitance formulation explaining the interfacial potential. Unlike previous models we created a unified model where the sensing interface and the FET are coupled and the system is solved as such without unnecessary simplifications used earlier. The model validity is verified by comparing the results with well-established ISFET models and with experimental results.

Continuous, real-time monitoring of the level of pH and free chlorine in drinking water is of great importance to public health. However, it is challenging when conventional analytical instruments, such as bulky pH electrodes and expensive free chlorine meters, are used. These instruments have slow response, are difficult to use, prone to interference from operators, and require frequent maintenance. In contrast, microfabricated electrochemical sensors are cheaper, smaller in size, and highly sensitive. Therefore, these sensors are desirable for online monitoring of pH and free chlorine in water. In this review, we discuss different physical configurations of microfabricated sensors. These configurations include potentiometric electrodes, ion-sensitive field-effect transistors, and chemo-resistors/transistors for electrochemical pH sensing. Also, we identified that micro-amperometric sensors are the dominant ones used for free chlorine sensing. We summarized and compared the structure, operation/sensing mechanism, applicable materials, and performance parameters in terms of sensitivity, sensing range, response time and stability of each type of sensor. We observed that novel sensor structures fabricated by solution processing and operated by smart sensing methodologies may be used for developing pH and free chlorine sensors with high performance and low cost. Finally, we highlighted the importance of the concurrent design of materials, fabrication processes, and electronics for future sensors.

Humidity sensors have several applications in both industrial processing and environmental control. Pure and doped hematite has proved to exhibit remarkable humidity sensing properties. The aim of this investigation is to study the effect of doping of some metal ions (Li + ,Mg +2 , Ba +2 , Sr +2 , and Na +) onto the crystalline hematite and to determine their sensitivity towards relative humidity (RH). The obtained crystalline samples were characterized by X-Ray Diffraction (XRD) combined with Field Emission Scanning Electron Microscopy (FESEM). The doped sodium metal ions (Na +) hematite sample showed a significant response towards relative humidity at room temperature.

Abstract:  Monodisperse polystyrene nanoparticles with a diameter of 173 nm were incorporated into a polydimethylsiloxane matrix where they display an iridescent color that can be attributed to the photonic crystal effect. The film is violet in plain water, but turns to red in the presence of the non-polar solvent n-hexane. Several solvents were studied. The films are capable of monitoring the water content of ethanol/water mixtures, where only 1% of water leads to a shift of the peak wavelength of reflected light by 5 nm. The method also can be applied to determine, both visually and instrumentally, the fraction of methanol in ethanol/methanol mixtures. Here, a fraction of 1% of methanol results in a wavelength shift of 2 nm. The reflected wavelength is not influenced by temperature changes nor impeded by photobleaching. The signal changes are fully reversible, and response times are <1 s.
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The Thio Schiff-Base (TSB) was used as an excellent ionophore in the construction of a Tm3+ PVC-based membrane sensor. The constructed PVC membrane sensor containing TSB exhibits a
Nernstian response of 20.1 ± 0.3 mV per decade for Tm3+ ions over a wide concentration range between 1.0×10-7 and 1×10-2 M, with a limit of detection of 8.6 ×10-8 M. It has a fast response
time (<10 s), operates well in the pH range of 3.0–8.7. The best performance was obtained with a membrane composition of 30% poly(vinyl chloride), 55% o-nitrophenyloctyl ether (NPOE), 4%
TSB, 10% oleic acid (OA) and 1% sodium tetraphenyl borate (NaTBP).

A chemical sensor is a device that transforms chemical information (composition, presence of a particular element or ion, concentration, chemical activity, partial pressure.) into an analytically useful signal. The chemical information, mentioned above, may originate from a chemical reaction of the analyte or from a physical property of the system investigated. They can have applications in different areas such as medicine, home safety, environmental pollution and many others.

The health diagnosis of agricultural structures is critical to detecting damages such as cracks in concrete, corrosion, spalling, and delamination. Agricultural structures are susceptible to environmental degradation due to frequent exposure to water, organic effluent, farm chemicals, structural loading, and unloading. Various sensors have been employed for accurate and real-time monitoring of agricultural building structures, including electrochemical, ultrasonic, fiber-optic, piezoelectric, wireless, fiber Bragg grating sensors, and self-sensing concrete. The cost–benefits of each type of sensor and utility in a farm environment are explored in the review. Current literature suggests that the functionality of sensors has improved with progress in technology. Notable improvements made with the progress in technology include better accuracy of the measurements, reduction of signal-to-noise ratio, and transmission speed, and the deployment of machine learning, deep learning, and arti...

Herein we review aspects of leading-edge research and innovation in Materials Science that exploits big data and Machine Learning (ML), two computer science concepts that combine to yield computational intelligence. ML can accelerate the solution of intricate chemical problems and even solve problems that otherwise would not be tractable. But the potential benefits of ML come at the cost of big data production; that is, the algorithms demand large volumes of data of various natures and from different sources, from materials properties to sensor data. In the survey, we propose a roadmap for future developments with emphasis on computer-aided discovery of new materials1 and analysis of chemical sensing compounds, both prominent research fields for ML in the context of Materials Science. In addition to providing an overview of recent advances, we elaborate upon the conceptual and practical limitations of big data and ML applied to Materials Science, outlining processes, discussing pitfalls, and reviewing cases of success and failure.

A poly(vinyl chloride) (PVC)-based membrane sensor for Tb3+ ions was prepared by employing 1, 3-Diaminopropane-N,N,N',N'-tetraacetic acid (APTAA) as an ionophore, sodium tetraphenyl
borate (NaTPB) as an anion excluder, and dibutylphthalate (DBP), benzylacetate (BA), acetophenon (AP) and nitrobenzene (NB) as plasticizing solvent mediators and investigated as a
selective membrane sensor. The sensor displays a linear dynamic range between 1.0×10−8 and 1.0×10−2 M, with a nice Nernstian slope of 19.8±0.4 mV per decade and a detection limit of 8.4×10−9 M. The proposed sensor displays a fast response time (~5 s). The potentiometric response is independent of pH in the range of 2.1–9.5.

Two new highly selective colorimetric and fluoregenic aminopyridine Schiff bases (L1 and L2) were synthesized by simple refluxing method and characterised via standard NMR and HRMS techniques. Its excellent metal sensing abilities explored on absorbance and fluorescence spectroscopy. The recognition colorimertric sensing behavior of probes L1 and L2 towards Ni(II), Zn(II), Fe(III) and UO 2 (II) ions were carefully investigated with different aspects of sensing behavior such as sensitivity, binding constant , stoichiometry, pH range and interference effect. Moreover, L1 and L2 also displayed excellent " off-on " fluoregenic selectivity with Zn(II). The results revealed that the sensors provided colorimetric and fluoregenic sensing excellent response with low limit of detection, under neutral conditions.

A Surface Acoustic Wave (SAW) gas sensor is designed and tested in this paper. The objective of the designed SAW Gas sensor is to detect H2S and NOX gases. The inter-digital transducers (IDT) antennas in the proposed sensor are coated with thin film WO3, which mass is sensitive to mentioned gas concentrations upon close contact. The changes in WO3 mass are registered as frequency shift from 300 to 500 MHz. The sensor blocks are simulated, fabricated and tested for an operating frequency of 300 MHz to 350 MHz. A relatively linear response is achieved with a step of 0.1 V for 10 MHz step frequency shift emitted from WO3 coated IDTs. This fully integrated signal processing circuitry designed by 0.18 mm CMOS process is simple, cost effective, small in size, has low power consumption, and fast real-time operation response as well.

A novel thulium (III) membrane sensor showing a Nernstian response of 20.4±0.3 mV per
decade of thulium concentration in the concentration and pH ranges of 1.0× 10-6 to 1.0× 10-
2 mol L-1 and 3.4-8.6 respectively is prepared based on the incorporation of 1, 1'-(1, 4-
butanediyl) bis (imidazole)(BYI) into a polymeric membrane sensor. The sensor had a satisfactory selectivity behavior with respect to alkaline, alkaline earth, transition and heavy
metal ions and was successfully used in the determination of the fluoride ion in two mouth ...

We have designed and synthesized off–on fluorometric probes, 7-(but-3-yn-1-yloxy)-8-(difluoromethyl)-2H-chromen-2-one (AYF) and 7-((4-(tert-butyldiphenylsilyloxy)benzyl)oxy)-8-(difluoromethyl)coumarin (DPF 1), by incorporating the concept of biological signal transduction strategy into their molecular design and present their proof-of-concept demonstration for mercury (Hg 2+) detection. AYF undergoes a cascade of self-immolative reactions in the presence of Hg 2+ and unmasks fluorogenic coumarin 1 and releases two latent fluoride ions. These fluorides initiate the removal of silyl protecting trigger group on DPF 1 which directs another cascade of self-immolative reactions. The fluoride ions (amplifiers) are continuously activating the cascade reaction, and, as a result, coumarin 1 progressively accumulates in the reaction medium and the whole process accelerates an amplified signal for Hg 2+. For detection of Hg 2+ , the limit of detection of the two-probe coupling assay (AYF and DPF 1) is 0.51 ppb which is more than 2000 times lower than that of AYF alone. Besides, 3-(benzothiazol-2-yl)-4-carbonitrile-7-((4-(tert-butyldiphenylsilyloxy)benzyl)oxy)coumarin (DCC), a long-wavelength probe, was coupled with AYF and DPF 1 in order to shift the emission to a higher wavelength region. Negative control studies revealed that the probes undergo controlled and organized sensing pathways as we designed.

A new selective and sensitive Tb3+-PVC membrane sensor was developed using an ion carrier named 1,4-bis[o-(furan-2-carboxamidophenyl)]-1,4-dithiobutane (FCT). The sensor has a linear dynamic range between 1.0×10-7-1.0×10-2 M, with a near Nernstian slope of 20.7 ± 0.2 mV per decade, a detection limit of 7.5×10-8 M with a membrane composition of 30% poly(vinyl
chloride), 66% dibutyl phthalate (DBP), 2% sodium tetraphenyl borate and 2% FCT. The potentiometric response of the proposed electrode is pH independent in the range of 2.5–7.8. The response time was relatively quick in the whole concentration range (~ 5 s). To investigate the membrane sensor selectivity, its potential response was determined in the presence of various
interfering foreign cations using the matched potential method. This sensor demonstrated good selectivity and sensitivity towards the terbium ion for a broad variety of cations, including alkali,
alkaline earth, transition and heavy metal ions. The developed sensor was successfully applied as an indicator electrode in the Tb(III) ion potentiometric titration with EDTA.

Farm-to-table operations produce, transport, and deliver produce to consumers in very different ways than conventional, corporate-scale agriculture operations. As a result, the time it takes to get a freshly picked fruit to the consumer is relatively short and the expectations of the consumer for freshness and quality are high. Since many of these operations involve small farms and small businesses, resources to deploy sensors and instruments for monitoring quality are scarce compared to larger operations. Within stringent power, cost, and size constraints, this article analyzes chemical sensor technologies suitable for monitoring fruit quality from the point of harvest to consumption in farm-to-table operations. Approaches to measuring sweetness (sugar content), acidity (pH), and ethylene gas are emphasized. Not surprisingly, many instruments developed for laboratory use or larger-scale operations are not suitable for farm-to-table operations. However, there are many opportunities still available to adapt pH, sugar, and ethylene sensing to the unique needs of localized farm-to-table operations that can help these operations survive and expand well into the future.

Although significant progress is made in identifying pH sensing materials
and device configurations, a standard protocol for benchmarking performance
of next-generation pH devices is still lacking. In particular, key properties of
characterization systems, such as inherent component contributions, time
plots for extended-gate field-effect transistor (EGFET) measurements, and the
input resistance (Rin), often go unreported in studies of pH sensing systems.
These properties strongly influence the characterization system and can lead
to mistaken attribution of properties to the device. In this paper, a series
of essential characterization tests and parameters are reported to evaluate
pH systems, such as the zinc oxide EGFET, in a standardized protocol. This
EGFET ZnO sensor has a sensitivity of −58.1 mV pH−1, drift range from 2.5 to
14.2 µA h−1, and response time of 136 s. By using a ZnO sensing electrode,
it is demonstrated that i) intrinsic contributions of reference electrode and
commercial transistor (for EGFET) are not negligible; ii) time plots for EGFET
configuration and defining a critical point at the onset of drift are essential for
accurate sensitivity, response time, and drift reporting; and iii) the results of
the pH sensing system are strongly dependent on the input resistance of the
used characterization instruments.

Bitter melon (Momordica charantia) contains charantin that responsible for
the antidiabetic activity. Therefore, it is important to determine charantin in
the extracts for the purposed of its formulation or quality control. Herein, we
proposed a novel scanometric assay for charantin determination in the bitter
melon extracts based on immobilized silver nitrate and methylene blue as a
colorimetric paper. The presence of charantin can be detected simply via the color
change from blue to green and can be quantified using a scanner via the ImageJ
software. The proposed charantin sensor has a response time of 8 mins with the
linear range of 300 to 1000 µg/mL and the detection limit was 216.25 µg/mL.
The sensor has good reproducibility (RSD = 2.86%) with the stability up-to 5
months. The sensor was applied to determine charantin in the sample extracts,
and the result shown in a good agreement with TLC method.

A Tm(III) ion-selective membrane sensor was fabricated from polyvinyl chloride (PVC) matrix membrane containing N,N’-bis(pyridine-2-carboxamido)-2-aminobenzylamine (BPCA) as a neutral carrier, sodium tetraphenyl borate (NaTPB) as anionic excluder, and nitrobenzene (NB) as a plasticizing solvent mediator. One of the most important characteristics of any membrane sensor is its relative response for the primary ion over other ions present in solution, usually expressed in terms of potentiometric selectivity coefficient. In this work, the so-called mathed potential method was used for determination of selectivity coefficients of the sensor. The sensor possesses the advantages of very good selectivity over a large number of cations, especially, for lanthanide ions (Dy3+, Tb3+, Gd3+, Er3+, Lu3+, Eu3+, Ho3+, Nd3+, Pr3+, La3+, Yb3+, Ce3+, and Sm3+). To assess its analytical applicability the proposed Tm(III) sensor was successfully applied as an indicator electrode in the titration of Tm(III) ion solutions with EDTA.

A  new  sensitive  and  selective  poly(vinyl  chloride)-based embrane  sensor  for  aluminum  ions  was prepared  by  employing  on 1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane  (PCD)  as  an neutral  ion  carrier  and  investigated  as  a  selective  membrane  sensor.  The  electrode  exhibits  a  near Nernstian  response  (19.4±0.3  mVdecade-1 )  for  Al3+ ions  over  a  wide  concentration  range  from 1.0×10−6 to 1.0×10−2 mol L-1 with a limit of detection of 6.3×10−7 mol L-1 in  a pH range of 2.0–4.2.
The  best  performance  was  obtained  with  membrane  composition  30%  poly(vinyl  chloride),  66%  nitrobenzene,  2%  sodium  tetraphenylborate  and  2%  ionophore  PCD.  It  has  relatively  fast  response time (~5 s) and can be used at least for 2 months without any considerable divergence in potentials. This  sensor  revealed  a  great  enhancement  in  selectivity  coefficients  for  aluminum(III)  ions  in comparison with the previously reported aluminum(III) sensors. It was used as an indicator electrode in potentiometric titration of Al3+
with EDTA.

The health diagnosis of agricultural structures is critical to detecting damages such as cracks in concrete, corrosion, spalling, and delamination. Agricultural structures are susceptible to environmental degradation due to frequent exposure to water, organic effluent, farm chemicals, structural loading, and unloading. Various sensors have been employed for accurate and real-time monitoring of agricultural building structures, including electrochemical, ultrasonic, fiber-optic, piezoelectric, wireless, fiber Bragg grating sensors, and self-sensing concrete. The cost-benefits of each type of sensor and utility in a farm environment are explored in the review. Current literature suggests that the functionality of sensors has improved with progress in technology. Notable improvements made with the progress in technology include better accuracy of the measurements, reduction of signal-to-noise ratio, and transmission speed, and the deployment of machine learning , deep learning, and artificial intelligence in smart IoT-based agriculture. Key challenges include inconsistent installation of sensors in farm structures, technical constraints, and lack of support infrastructure , awareness, and preference for traditional inspection methods.

This study focuses on the measurement and performance of bio-filler composite
based on polyaniline (PANI)/chicken eggshell (CES). The composite films were
prepared via ex-situ polymerisation using DBSA as its dopant. The PANI solution was
distributed equally before mixing it with three different ratios of CES powder.
Characterisations of the composite films were analysed using Fourier-transform
infrared spectroscopy (FTIR) and Ultraviolet-visible spectroscopy (UV-Vis), Scanning
electron microscope/energy dispersive x-ray (SEM/EDX) and multimeter. PANI film
that contained 20mg CES filler possessed the highest conductivity and the fastest time to
achieve 90% of sensitivity. The film was also very selective towards ammonia gas and can
be reused up to eight cycles. All data reported in this study proved that PANI film with
20mg CES filler can act as a sensitive sensor with 6 ppm limit of detection.

The present report highlights the role of comprehensive structure property relationships (SPRs) in the discovery of a new and more effective molecular system for sensing purposes. From an extensive survey of different classes of amino substituted annulated furanones, it was realized that with some exceptions, these functionalized furanones could sense Cu 2+ ions in the semi-aqueous phase irrespective of the nature of substituents; furthermore the same scaffolds could also detect Al 3+ , if the aldehydic position is specifically filled by a 3-indoyl group. As a result, amino substituted annulated furanones with 3-indoyl groups could detect both metal ions, response time of which mainly depends on the overall molecular framework. After replacing different furanone frameworks, a dual metal ion sensor (for Cu 2+ and Al 3+) with short response time and high selectivity and association constant was identified. The proposed bifunctional sensor displayed a distinct but observable response (turn off colorimetric for Cu 2+ and turn on fluorescence for Al 3+) to both metal ions with potential applications in the area of real sample analysis and membrane sensing.