Conductometric Sensors Research Articles

ZnO Nanowires/Self-Assembled Monolayer Mediated Selective Detection of Hydrogen.

We are proposing a novel self-assembled monolayer (SAM) functionalized ZnO nanowires (NWs)-based conductometric sensor for the selective detection of hydrogen (H2). The modulation of the surface electron density of ZnO NWs due to the presence of negatively charged terminal amine groups (-NH2) of monolayers leads to an enhanced electron donation from H2 to ZnO NWs. This, in turn, increases the relative change in the conductance (response) of functionalized ZnO NWs as compared to bare ones. In contrast, the sensing mechanism of bare ZnO NWs is determined by the chemisorbed oxygen ions. The functionalized ZnO NWs exhibit an eight times higher response compared to bare ZnO NWs at an optimal working temperature of 200 °C. Finally, in comparison to studies in the literature involving strategies to enhance the sensing performance of metal oxides toward H2, like decoration with metal nanoparticles, heterostructures, and functionalization with a metal-organic framework, etc., SAM functionalization showed superior sensing results.

Effect of spacing, concentration of NaCl solution, and biasing of graphite electrodes towards conductometric sensor response

Effect of spacing, concentration of NaCl solution, and biasing of graphite electrodes towards conductometric sensor response

Chemosensitive Properties of Electrochemically Synthesized Poly-3-Thienylboronic Acid: Conductometric Detection of Glucose and Other Diol-Containing Compounds under Electrical Affinity Control.

Due to the presence of the boronic acid moieties, poly-3-thienylboronic acid has an affinity for saccharides and other diol-containing compounds. Thin films of this novel chemosensitive polymer were synthesized electrochemically on the gold surface. The adhesion of the polymer was enhanced by the deposition of a monomolecular layer of thiophenol. The technology was used to fabricate conductometric sensors for glucose and other diol-containing compounds. Simultaneous two- and four-electrode conductivity measurements were performed. The chemical sensitivity to sorbitol, fructose, glucose, and ethylene glycol was studied at different pH and electrode potentials, and the corresponding binding constants were obtained. Depending on the electrode potential, the reciprocal values of the binding constants of glucose to poly-3-thienylboronic acid at neutral pH are in the range of 0.2 mM-1.0 mM. The affinity for glucose has been studied in buffer solutions and in solutions containing the major components of human blood. It was shown that the presence of human serum albumin increases the affinity of poly-3-thienylboronic acid for diol-containing compounds.

Conductometric H2S Sensors Based on TiO2 Nanoparticles.

High-performance hydrogen sulfide (H2S) sensors are mandatory for many industrial applications. However, the development of H2S sensors still remains a challenge for researchers. In this work, we report the study of a TiO2-based conductometric sensor for H2S monitoring at low concentrations. TiO2 samples were first synthesized using the sol-gel route, annealed at different temperatures (400 and 600 °C), and thoroughly characterized to evaluate their morphological and microstructural properties. Scanning electronic microscopy, Raman scattering, X-ray diffraction, and FTIR spectroscopy have demonstrated the formation of clusters of pure anatase in the TiO2 phase. Increasing the calcination temperature to 600 °C enhanced TiO2 crystallinity and particle size (from 11 nm to 51 nm), accompanied by the transition to the rutile phase and a slight decrease in band gap (3.31 eV for 400 °C to 3.26 eV for 600 °C). Sensing tests demonstrate that TiO2 annealed at 400 °C displays good performances (sensor response Ra/Rg of ~3.3 at 2.5 ppm and fast response/recovery of 8 and 23 s, respectively) for the detection of H2S at low concentrations in air.

Versatile conductometric biosensors for rapid and selective detection of inflammatory and cardiac biomarkers in saliva

Biosensors have become promising alternatives to the conventional methods in early identification of diseases. However, translation of biosensors from lab to commercial products have challenges such as complex sensor fabrications and complicated detection, and inadequate sensitivity and selectivity. Here, we introduce simple and low-cost fabricated conductometric sensors based on high resistivity silicon wafers (HR-Si) which can be adopted to functionalise with both natural and synthetic antibodies in detecting five biomarkers including interleukin-6, C reactive protein, cardiac troponin I, brain natriuretic peptide, and N terminal-probrain natriuretic peptide. All five biomarkers show selective and rapid (10 min sample incubation and <1 min of reading time) detection in both media of phosphate buffer saline and saliva with the detection limits lower than that of reported healthy levels in saliva. This work highlights the versatility of HR-Si sensors in functionalisation of both natural and synthetic antibodies in sensitive and selective biomarker detection. As these miniaturised conductometric biosensors can be easily modified with on-demand biomaterials to detect corresponding target biomarkers, they enable a new category of compact point-of-care medical devices.

II-VI Semiconductor-Based Conductometric Gas Sensors: Is There a Future for These Sensors?

A review of the state of research in the development of conductometric gas sensors based on II-VI semiconductors is given. It was shown that II-VI compounds indeed have properties that are necessary for the development of highly efficient gas sensors. In this case, to achieve the required parameters, all approaches developed for metal oxides can be used. At the same time, during a detailed review, it was concluded that sensors based on II-VI compounds have no prospects for appearing on the gas sensor market. The main obstacle is the instability of the surface state, which leads to poor reproducibility of parameters and drift of sensor characteristics during operation.

Conductometric n-butanol sensor based on Pt-loaded LaFeO3 with 3D hierarchical structure

In this work, platinum nanoparticles (NPs) were loaded on the surface of LaFeO3 by wet impregnation method. Various characterization methods were carried out to confirm the microstructure of the samples, and the results showed that the as-prepared LaFeO3 has a 3D hierarchical structure composed of 2D walls of nanoparticles. Gas sensing research shows that the response of the composite loaded with Pt is increased by 2.25 times, and the response/recovery time is reduced from 220 s/214 s to 146 s/131 s, which is a comprehensive reduction of 34 % and 39 %. The material has good selectivity, and the detection limit reaches 100 ppb∼1.38. This enhancement can be attributed primarily to two factors: the formation of a Schottky barrier between the Pt nanoparticles and LaFeO3, where Pt acts as a center of electronic sensitization with a negative charge on the (002) surface of LaFeO3; and the efficient adsorption of oxygen species. First-principle calculations were employed to investigate the adsorption energy of the n-butanol molecule and to identify the advantages of oxygen species adsorption sites on the Pt-LaFeO3 surface compared to LaFeO3 alone. This work not only offers a promising solution for n-butanol sensors with extremely low detection limits but also identifies the most likely forms of gas adsorption and adsorption sites through theoretical calculations, providing a theoretical foundation for the further development of similar sensors.

Rapid Conductometric Sensing of Chronic Kidney Disease Biomarkers: Specific and Precise Detection of Creatinine and Cystatin C in Artificial Saliva

AbstractChronic kidney disease (CKD) has asymptomatic early stages, whereby early detection is crucial to prevent its complications and progression. Creatinine and cystatin C (cysC) assays are known for assessing kidney function but there are limited point‐of‐care diagnostics which are rapid, precise, and easy to use. Here, high resistivity silicon conductometric sensors for detection of creatinine and cysC with a 10 min sample incubation is introduced. The sensors provide resistance‐based signals that can be quantified and measured wirelessly. The sensors successfully detect creatinine and cysC in both phosphate buffer saline (PBS) and artificial saliva in the nanomolar range, being able to distinguish their critical concentrations at 8.8 and 20 nm, respectively, for diagnosis of early stage of CKD. The detection limit for both creatinine and cysC is determined as 0.01 nm which is more than 500× and 1000× times lower than critical concentrations for the two biomarkers, respectively. Finally, these sensors are incorporated into a battery‐free, miniaturized electronic device for wireless biomarker detection as a proof‐of‐concept demonstration of a point‐of‐care tool for assessing kidney functionality.

Conductometric Sensor Based on Electropolymerized Pyrrole-Tailed Ionic Liquids for Acetone Detection

Conductometric Sensor Based on Electropolymerized Pyrrole-Tailed Ionic Liquids for Acetone Detection

Waste cigarette butts-templated synthesis of in-situ graphitic carbon-doped ZnO fibers boosting dual-selectivity NO2/butanone at different temperatures

How to build a dual-selective ZnO-based gas sensor remains challenging due to the fact that the great majority of reported gas sensors were designed to monitor only a single given harmful gas. Herein, discarded cigarette butts were chose as template, and dipped in zinc nitrate solution. Then, the obtained precursors were calcined to synthesize two types of ZnO-based fibers with V-shaped grooves. Among, the fiber component (GC/ZnO, GC being graphitic carbon) calcined at 400 °C composes of 7.02 wt% GC and small nanoparticles, which possesses multistage mesopores, large specific surface area and abundant oxygen vacancies. These factors not only optimize the percentage and state of oxygen species adsorbed in sensing layer, but also expose more active sites and facilitate surface chemical reactions, thereby providing a dual-selective platform for different gases. The GC/ZnO sensor shows high response of 624 for 10 ppm NO2 at 92 °C, and good response of 22.5 for 100 ppm butanone at 170 °C. Also, it has reversible response-recovery, low detection limit, as well as satisfactory stability and humidity resistance. This is the first report on a conductometric sensor that achieves the rapid and accurate detection of above harmful gases. In addition, its temperature-controlled dual-functional sensing mechanism was also analyzed.

Predicting Ozone Depletion using BIn2O3 With RH based Solid Conductometric Sensor

&lt;p&gt;Ozone depletion arises due to the presence of gases like chlorofluorocarbons and halons which are liberated into the atmosphere. The region of earth’s atmosphere named as ozone shield, in which absorbs the ultra violet radiations of the sun. Although, its thickness varies periodically, this layer is primarily located in the lower stratosphere between 15 to 35 kms above the earth. Due to this, the ultraviolet rays directly enter into the earth causes harmful effects little by little on both living and non-living organisms. In this paper, BIn2O3 with rh sensor in co precipitation method is used to detect the ozone depletion and it is based on the solid-state gas sensors. To achieve the excellent performance of an ozone depletion detecting branch like BIn2O3 with rh, this was designed using a simple precipitation method. The coprecipitation method had deposited in BIn2O3 with a thickness of 45 to 50 nanometer. The detection limit of ozone reduced as 30 parts per billion. Further, the gas detector demonstrated high sensitivity and selectivity of the device. The rhodium covers the surface areas ranges from 0 to 0.1. It reaches the accuracy of 96%. According to the degree of rhodium coverage, the sensors will be response to the ozone gas. The oxygen chemisorbed ability and a coverage of a great surface area of BIn2O3 with rhodium highly related to the excellent sensing behavior. This study paves the way for an exact sensing and ppb level detection ozone gas.&lt;/p&gt;&#x0D;

Energy-efficient NO2 sensors based on two-dimensional layered 2H-WS2 nanosheets

Layered transition metal dichalcogenides (TMDCs) are considered among the next-generation materials for gas sensing. Here, we report exfoliated 2 H-WS2 nanosheets for the fabrication of highly performing NO2 sensors. Thermal annealing at several temperatures was performed to investigate the oxidation of WS2. The long-term stability of 2 H-WS2 bulk was verified. Using droplet variation method, three batches of conductometric sensors from 2 H-WS2 dispersions were fabricated on electrical transducers, namely two layers (2 L), five layers (5 L) and ten layers (10 L) WS2 nanosheets. These sensors were tested towards low NO2 concentrations at different temperatures (Room Temperature (20 ℃), 50 ℃ and 100 ℃) and relative humidity (RH) levels (20%, 40%, 60%, 80% and 90% RH). 2 L-WS2 based sensor showed the highest response at room temperature (RT). Excellent repeatability (4 cycles) towards 1 ppm NO2 and long-term stability (more than two months) were achieved. Full selectivity towards NO2 (1 ppm) at RT was observed over NH3 (15 ppm), H2S (15 ppm), ethanol (30 ppm) and acetone (30 ppm). Our results confirm that low-power consumption devices with high sensitivity (even at high RH), long-term stability and excellent selectivity towards NO2 were fabricated using 2 H-WS2 nanosheets.

Electronic control and measurement unit of conductometric nitrogen dioxide sensor in the atmosphere

High levels of air pollution lead to various negative consequences, including deterioration in public health. One of the main air pollutants in industrial cities is nitrogen dioxide. Nitrogen dioxide (NO2) is produced by various industrial processes. It is highly toxic and can cause various diseases such as bronchitis, asthma and other respiratory diseases. Despite all efforts to reduce NO2 emissions, the problem of air pollution remains relevant. Therefore, it is important to continue research into the development of new methods for continuous atmospheric monitoring and timely detection of emissions. One of the main tasks of the modern branch of science in the development of a monitoring system is the development of a sensitive, reliable and inexpensive gas sensor for NO2 in the air. The tasks of this work are design, construct, assemble and test a new original electronic control and measurement unit for a previously developed conductometric sensor for nitrogen dioxide in the atmosphere which is capable of recording and interpreting the signal in the form of a numerical response and displaying it on the screen. As a result of the work carried out, a new original electronic control and measurement unit was developed and constructed for the previously developed conductometric gas sensor for nitrogen dioxide in the atmosphere which is capable of recording and interpreting the signal in the form of a numerical response and displaying it on the screen. The developed device was tested in a system with a gas sensor with a p-type semiconductor gas-sensitive element. It has been established that for a model atmosphere of 50 ppm NO2 + N2, the sensor response recorded by the developed device is equal to (10,4 ± 0,2)∙10-3, and for a model atmosphere of 10 ppm NO2 + N2 – (6,2 ± 0,2)∙10-3. The obtained values can be used to determine the concentration of nitrogen dioxide under real atmospheric monitoring conditions.

Approaches for selectivity improvement of conductometric gas sensors: an overview

Conductometric gas sensors (CGS) have been extensively explored in recent decades owing to easy fabrication and miniaturization, low cost and distributable detectability.

Gas-Sensing Properties and Mechanisms of 3D Networks Composed of ZnO Tetrapod Micro-Nano Structures at Room Temperature.

Metal oxide semiconductors (MOSs) hold great promise for electronic devices such as gas sensors. The utilization of ZnO as a conductometric gas sensor material can be traced back to its early stages; however, its application has primarily been limited to high-temperature environments. A gas sensor based on highly porous and interconnected 3D networks of ZnO tetrapod (ZnO-T) micro-nano structures was fabricated via an easy chemical vapor deposition (CVD) method. Homemade instruments were utilized to evaluate the gas-sensing of the sample at room temperature. It exhibited good gas-sensing at room temperature, particularly with a response of up to 338.80% toward 1600 ppm ethanol, while also demonstrating remarkable repeatability, stability, and selectivity. Moreover, the unique gas-sensing properties of ZnO-T at room temperature can be reasonably explained by considering the effect of van der Waals forces in physical adsorption and the synergistic effect of carrier concentration and mobility. The aforementioned statement presents an opportunity for the advancement of gas sensors utilizing ZnO at room temperature.

Amorphous Pt-decorated α-Fe2O3 sensor with superior triethylamine sensing performance prepared by a one-step impregnation method

Noble metals are widely used additives to improve the sensing performance of conductometric metal oxide gas sensors. Although amorphous noble metal particles are expected to further improve the gas sensor response, common techniques often result in crystalline nanoparticles. Herein, an amorphous Pt nanoparticle-decorated α-Fe2O3 sensor was prepared via a temperature-controlled facile one-step impregnation method without the use of a reductant, surfactant, or subsequent thermal reduction. The amorphous Pt-functionalized α-Fe2O3 exhibited superior sensing performance to triethylamine, achieving 100 °C and 140 °C decreases in the optimal working temperature, and had better selectivity, with 22-fold and 14-fold improvements in gas response when compared to those of crystallized Pt-functionalized α-Fe2O3 and pristine α-Fe2O3, respectively. The as-prepared amorphous Pt-decorated α-Fe2O3 sensor showed great promise as a promising triethylamine sensor, and the newly developed facile impregnation method was shown to be an effective strategy to synthesize amorphous noble metal-decorated metal oxide gas sensors.

Deposition of Composite Nanoparticle-Based Thin Films for Gas Sensing

Working principle of conductometric gas sensors is based on modulation in electrical conductivity of the sensing material due to adsorption-desorption reactions between the target gas and the sensor surface. Nano-structuring the sensing material increases the effective surface area for interaction between the target gas and the sensing material thereby enhancing the sensorial response. Metal oxide semiconductors (MOS) have shown remarkable sensing performance to oxidizing and reducing gases. The combination of different MOS has often demonstrated to synergistically improve the gas sensing performance via the formation of highly sensitive heterojunctions at their interface.In this work, we deposited thin films composed of nanoparticles (NPs) of p-type CuOx and n-type WOx to enhance the effective surface area of the material and to realize the maximum number of nano p-n heterojunctions in the material. The films were prepared using the Nanogen-Trio NP source equipped with three 1′′ magnetrons, mounted on a custom-built deposition chamber and sputtered by a DC power supply. Depositions were executed in Ar+O2 gas mixture. The O2 admixture may significantly enhance the mass flux of NPs. Furthermore, the O2 admixture allows one to tune the desired stoichiometry of the respective metal oxides. On the other hand, the pronounced hysteresis complicates the deposition of WOx NPs. The deposition process was controlled using an in-house developed software to prepare thin films composing a mixture of NPs with a defined volumetric ratio of the individual materials.This work demonstrates the versatility of our custom-built gas aggregation source that facilitates the preparation of multi-composite NP-based thin film giving the best sensorial response.

Conductometric study of hydroelectrochemical parameters for the interaction of cadmium bromide in lump and nano forms with Orange G dye

The hydroelectrochemical behaviour of cadmium bromide was investigated in the presence of the dye Orange G. This information can be used to develop conductometric sensors for detecting these substances, understand how they behave in aqueous solutions, and design effective procedures for removing the extremely toxic heavy cadmium ions from contaminated water sources. The hydroelectrochemical parameters for the interaction between lump and nanoCdBr2 with Orange G dye were investigated conductometrically in aqueous solutions at different temperatures. CdBr2 interacts with Orange G as a ligand, resulting in a decrease in conductivity. However, the interaction was more significant with nanoCdBr2, which showed a higher decrease in conductivity compared to lump CdBr2. Two stiochiometric complexes, 1:1 and 1:2, were produced; Kf and ΔGf are higher for 1:1 than for 1:2 (CdBr2/Orange G). With rising temperatures, the formation constants decreased, and the negative sign of ΔGf indicated the spontaneity of the reaction, which increased with rising temperatures. The negative values of (ΔHf) revealed the complexation's exothermic nature, whereas the positive entropy (ΔS) values confirmed that the complex formation depended on molecular entropy since the complex formation was favored by an increase in molecular disorder. The results of our investigation can be utilised to enhance comprehension of the behaviour of these materials in aqueous solutions and create efficient protocols for the removal of very toxic heavy metal cadmium ions from polluted water sources. We think that our study advances the discipline and offers a distinctive viewpoint on this subject.

Metal Oxide Nanowire-Based Sensor Array for Hydrogen Detection.

Accurate hydrogen leakage detection is a major requirement for the safe and widespread integration of this fuel in modern energy production devices, such as fuel cells. Quasi-1D nanowires of seven different metal oxides (CuO, WO3, Nb-added WO3, SnO2, ZnO, α-Bi2O3, NiO) were integrated into a conductometric sensor array to evaluate the hydrogen-sensing performances in the presence of interfering gaseous compounds, namely carbon monoxide, nitrogen dioxide, methane, acetone, and ethanol, at different operating temperatures (200-400 °C). Principal component analysis (PCA) was applied to data extracted from the array, demonstrating the ability to discriminate hydrogen over other interferent compounds. Moreover, a reduced array formed by only five sensors is proposed. This compact array may be easily implementable into artificial olfaction systems used in real hydrogen detection applications.

Microfluidic Sensor Based on Cell-Imprinted Polymer-Coated Microwires for Conductometric Detection of Bacteria in Water.

The rapid, inexpensive, and on-site detection of bacterial contaminants using highly sensitive and specific microfluidic sensors is attracting substantial attention in water quality monitoring applications. Cell-imprinted polymers (CIPs) have emerged as robust, cost-effective, and versatile recognition materials with selective binding sites for capturing whole bacteria. However, electrochemical transduction of the binding event to a measurable signal within a microfluidic device to develop easy-to-use, compact, portable, durable, and affordable sensors remains a challenge. For this paper, we employed CIP-functionalized microwires (CIP-MWs) with an affinity towards E. coli and integrated them into a low-cost microfluidic sensor to measure the conductometric transduction of CIP-bacteria binding events. The sensor comprised two CIP-MWs suspended perpendicularly to a PDMS microchannel. The inter-wire electrical resistance of the microchannel was measured before, during, and after exposure of CIP-MWs to bacteria. A decline in the inter-wire resistance of the sensor after 30 min of incubation with bacteria was detected. Resistance change normalization and the subsequent analysis of the sensor's dose-response curve between 0 to 109 CFU/mL bacteria revealed the limits of detection and quantification of 2.1 × 105 CFU/mL and 7.3 × 105 CFU/mL, respectively. The dynamic range of the sensor was 104 to 107 CFU/mL where the bacteria counts were statistically distinguishable from each other. A linear fit in this range resulted in a sensitivity of 7.35 μS per CFU/mL. Experiments using competing Sarcina or Listeria cells showed specificity of the sensor towards the imprinted E. coli cells. The reported CIP-MW-based conductometric microfluidic sensor can provide a cost-effective, durable, portable, and real-time solution for the detection of pathogens in water.