Ion-sensitive Sensors Research Articles

Ni2+ ion sensitive sustainable sensors based on 4-vinyl pyridine-ethyl acrylate copolymer

Toxic metal ions present in environmental water samples and other samples need to be detected for their removal. The detection of trace metal ions using an ion selective electrode (ISE) holds great significance in analytical chemistry. A 4-vinyl pyridine-ethyl acrylate copolymer-polyvinyl chloride (VE-PVC) based polymeric matrix (electrode) has been fabricated by free radical bulk polymerization method which is an example of a green and sustainable method capable of detecting Ni2+ ions even in trace amounts. To fabricate the polymeric matrix (electrode) (PME), VE has been used as an ionophore. Further, the effectiveness of Ni2+ ion ISE has also been investigated in the presence of surfactants and detergents. Its performance has also been analyzed in the presence of plasticizers. The electrode is found to be very useful for the estimation of Ni2+ ions using ethylenediaminetetraacetic acid by potentiometric titration and also in the estimation of presence of Ni2+ ions in water. Compared to other metal ions, the fabricated membrane electrode developed in this work has been found to show efficient and better selectivity towards Ni2+ ions.

Ultrasensitive dopamine detection with graphene aptasensor multitransistor arrays

Detecting physiological levels of neurotransmitters in biological samples can advance our understanding of brain disorders and lead to improved diagnostics and therapeutics. However, neurotransmitter sensors for real-world applications must reliably detect low concentrations of target analytes from small volume working samples. Herein, a platform for robust and ultrasensitive detection of dopamine, an essential neurotransmitter that underlies several brain disorders, based on graphene multitransistor arrays (gMTAs) functionalized with a selective DNA aptamer is presented. High-yield scalable methodologies optimized at the wafer level were employed to integrate multiple graphene transistors on small-size chips (4.5 × 4.5 mm). The multiple sensor array configuration permits independent and simultaneous replicate measurements of the same sample that produce robust average data, reducing sources of measurement variability. This procedure allowed sensitive and reproducible dopamine detection in ultra-low concentrations from small volume samples across physiological buffers and high ionic strength complex biological samples. The obtained limit-of-detection was 1 aM (10–18) with dynamic detection ranges spanning 10 orders of magnitude up to 100 µM (10–8), and a 22 mV/decade peak sensitivity in artificial cerebral spinal fluid. Dopamine detection in dopamine-depleted brain homogenates spiked with dopamine was also possible with a LOD of 1 aM, overcoming sensitivity losses typically observed in ion-sensitive sensors in complex biological samples. Furthermore, we show that our gMTAs platform can detect minimal changes in dopamine concentrations in small working volume samples (2 µL) of cerebral spinal fluid samples obtained from a mouse model of Parkinson’s Disease. The platform presented in this work can lead the way to graphene-based neurotransmitter sensors suitable for real-world academic and pre-clinical pharmaceutical research as well as clinical diagnosis.

Magneto-controlled potentiometric assay for E. coli based on cleavage of peptide by outer-membrane protease T

Rapid, sensitive and reliable Escherichia coli (E. coli) detection and identification are critically important to protect public health. Here, we describe a magneto-controlled potentiometric assay for specific detection of E. coli cells by making use of the E. coli outer-membrane protease T (OmpT). OmpT is an endopeptidase that specifically cleaves peptide at dibasic sites. A rationally designed peptide serving as both OmpT substrate and potentiometric signal reporter was immobilized on magnetic beads. The rapid accumulation and extraction of peptide-functionalized magnetic beads on a polymeric membrane doped with an ion exchanger can be achieved using a magnetic force. The magnetic-field-assisted extraction of the peptide into the polymeric membrane ion-sensitive sensor, as confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, can lead to a rapid, stable and reproducible potential change. OmpT is capable of cleaving the positively charged peptide on the magnetic beads, thus resulting in charge density change. The change in charge density and subsequently the potential change can be readily detected and used for quantification of E. coli at levels down to 5.0 × 103 CFU mL−1. This work provides a versatile, rapid and reliable potentiometric method for E. coli detection.

Performance Evaluation of Innovative Ion-Sensitive Field Effect Diode for pH Sensing

In this paper, we have successfully introduced and characterized an innovative ion sensitive device called “Ion sensitive field effect diode”, a completely new ion-sensitive sensor. In conventional ion-sensitive devices, electrolyte/insulator interface reactions produce a conductive channel between the drain and the source whereas in our proposed structure, a p-n junction forms and is responsible for the conductivity. Since it is for the first time that such device is proposed as an ion sensor, comprehensive characterizations have been performed based on our previously TCAD-based model which was developed to simulate electrolyte and electrolyte/insulator interface. Considering this reliable model, sensing parameters of pH sensors, such as sensitivity and signal to noise ratio are investigated and evaluated. Meanwhile, an accurate model to approximate the noise behavior of the device is proposed. Moreover, the effect of Silicon active layer thickness and doping concentration on the sensitivity of the device has been studied. Results reveal that ion sensitive field effect diode can achieve sensitivity about five times higher than the Nernst limit and can be considered as a promising candidate toward accurate and more sensitive ion sensors and this new type of sensor deserves further attention and development.

Rapid detection of Klebsiella pneumoniae, Klebsiella oxytoca, Raoultella ornithinolytica and other related bacteria in food by lateral-flow test strip immunoassays

Bacteria of the genera Klebsiella and Raoultella, which are present in foods and the natural environment, are associated with health hazards in humans. In the present study, two types of strips-based methods were developed to detect these bacteria simply and quickly. One method used lateral-flow test strips (LFTS) in combination with anti-Klebsiella antibodies labeled with palladium nanoparticles that bind to target bacteria, allowing their visualization. In the other, the antibodies were immobilized on nitrocellulose membranes, and urease activity was measured using an ion sensitive field effect transistor pH sensor. Testing of a combination of these two methods on 72 cultured strains successfully identified all 25 strains of Klebsiella pneumoniae, Klebsiella oxytoca and Raoultella ornithinolytica. This approach also accurately identified 76 of 77 (99%) strains isolated from meats and pastries. When combined with preculture, this method was accurate in identifying 19 of 26 (73%) target bacteria in food. These results suggest that the novel combination of strip-based assays may be effective for the on-site monitoring of food production plants, and thereby enhance food safety.

The effects of pressure on pH of Tris buffer in synthetic seawater

Equimolar Tris (2-amino-2-hydroxymethyl-propane-1,3-diol) buffer prepared in artificial seawater media is a widely accepted pH standard for oceanographic pH measurements, though its change in pH over pressure is largely unknown. The change in volume (ΔV) of dissociation reactions can be used to estimate the effects of pressure on the dissociation constant of weak acid and bases. The ΔV of Tris in seawater media of salinity 35 (ΔVTris⁎) was determined between 10 and 30°C using potentiometry. The potentiometric cell consisted of a modified high pressure tolerant Ion Sensitive Field Effect Transistor pH sensor and a Chloride-Ion Selective Electrode directly exposed to solution. The effects of pressure on the potentiometric cell were quantified in aqueous HCl solution prior to measurements in Tris buffer. The experimentally determined ΔVTris⁎ were fitted to the equation ΔVTris⁎=4.528+0.04912t where t is temperature in Celsius; the resultant fit agreed to experimental data within uncertainty of the measurements, which was estimated to be 0.9cm−3mol−1. Using the results presented here, change in pH of Tris buffer due to pressure can be constrained to better than 0.003 at 200bar, and can be expressed as:∆pHTris=−4.528+0.04912tPln10RT.where T is temperature in Kelvin, R is the universal gas constant (83.145cm3barK−1mol−1), and P is gauge pressure in bar. On average, pH of Tris buffer changes by approximately −0.02 at 200bar.

Deep-Sea DuraFET: A Pressure Tolerant pH Sensor Designed for Global Sensor Networks.

Increasing atmospheric carbon dioxide is driving a long-term decrease in ocean pH which is superimposed on daily to seasonal variability. These changes impact ecosystem processes, and they serve as a record of ecosystem metabolism. However, the temporal variability in pH is observed at only a few locations in the ocean because a ship is required to support pH observations of sufficient precision and accuracy. This paper describes a pressure tolerant Ion Sensitive Field Effect Transistor pH sensor that is based on the Honeywell Durafet ISFET die. When combined with a AgCl pseudoreference sensor that is immersed directly in seawater, the system is capable of operating for years at a time on platforms that cycle from depths of several km to the surface. The paper also describes the calibration scheme developed to allow calibrated pH measurements to be derived from the activity of HCl reported by the sensor system over the range of ocean pressure and temperature. Deployments on vertical profiling platforms enable self-calibration in deep waters where pH values are stable. Measurements with the sensor indicate that it is capable of reporting pH with an accuracy of 0.01 or better on the total proton scale and a precision over multiyear periods of 0.005. This system enables a global ocean observing system for ocean pH.

An automated monitoring and control system for flow‐through co‐cycling hypoxia and pH experiments

AbstractAcidification research has exploded in recent years, however, experiments testing effects of co‐cycling hypoxia and pH on ecological and physiological processes are rare, despite the pervasiveness and potential importance of co‐varying fluctuations in these parameters. Co‐cycling dissolved oxygen (DO) and pH are difficult to precisely control, as gases used for manipulation influence both parameters. We successfully developed a LabVIEW™‐based system capable of monitoring and controlling co‐varying DO and pH in raw seawater flow‐through aquaria. Using feedback from Oxyguard DO probes and Honeywell ion sensitive field effect transistor Durafet pH sensors, our system controls ratios of nitrogen, oxygen, carbon dioxide, atmospheric air, and CO2‐stripped air within a total gas flow rate through mass flow controllers, to achieve target co‐cycling DO and pH values in five treatments. Our system performed well in two long‐term experiments investigating effects of diel‐cycling hypoxia and pH on eastern oyster (Crassostrea virginica) feeding, growth, fecundity, Perkinsus sp. (Dermo) infection dynamics and immune response. In our 2013 adult oyster experiment, the severe low DO treatment averaged only 0.04 mg L−1 higher than the 0.50 mg L−1 target, and the moderate hypoxia averaged only 0.05 mg L−1 higher than the 1.30 mg L−1 target over 48 d of cycles. Mean pH for the hypercapnia plateau was within 0.02 above the 7.00 target. In our 2013 spat experiment, daily minimum DO in the severe and moderate hypoxia treatments were both within 0.06 mg L−1 of the 0.50 and 1.3 mg L−1 targets, respectively; hypercapnia plateau pH values were within 0.01 of our 7.00 target.

Measuring velocity of water flow within a gravel layer using an electrolyte tracer method with a Pulse Boundary Model

Summary Water flow within a gravel layer is of great interest in many studies and applications. The electrolyte tracer method, based on the solution to the governing partial differential equation of solute transport in water flow under a pulse boundary condition, the Pulse Boundary Model, was suggested to measure the velocity of water flow within a gravel layer. Laboratory experiments were made to illustrate the measurement method. The dye tracer method was used to make comparative measurements. Gravel of about 2 cm in diameter was placed to a 5 cm thick layer in a flume of 4 m long, 20 cm wide and 50 cm deep. Flow velocities were measured at locations of 0.3, 0.6, 0.9, 1.2 and 1.5 m from the electrolyte tracer injector, which was 1 m from the water inlet, under 3 flow rates of 3, 6 and 12 L/min and for 3 slope gradients of 4°, 8° and 12°. Highly concentrated KCl solution was injected into the water flow within the gravel layer through a funnel. The solute transport processes were registered by the measurement system, as detected by the ion-sensitive sensors, before being used for flow velocity estimations at different locations. The measured flow velocity increased with slope gradient but was similar under the different flow rates used. The velocity values measured by the Pulse Boundary Model were about 20–50% lower than those estimated by the dye tracer method although they were strongly linearly correlated. The measured velocity values were in about the same order of magnitude as those reported in the literature. Therefore, the Pulse Boundary Model electrolyte tracer method was demonstrated to be rational and applicable for measuring the velocity of water flow within a gravel layer.

Development of a low-hysteresis and high-linearity extended gate field-effect transistor-based chloride ion-sensitive microsensor

A low-hysteresis voltage and high-sensing linearity chloride ion-sensitive sensor based on an extended gate field-effect transistor (EGFET) for real-time water quality monitoring microsystem applications is presented. All of the EGFET-manufacturing processes adopted in this work are compatible with standard integrated circuits planar technology, and therefore, they are very suitable for the mass production. Two EGFET-based chloride ion-sensitive microsensors having same channel width/length ratio (1000 μm/10 μm ) but with different channel geometries (rectangular and annular types) are presented. At pCl 3 (log[Cl − ]=−3 ) test point, a very small hysteresis voltage of the rectangular- and annular-channels EGFET-based Cl − microsensors (5 and 7 mV, respectively) can be achieved. As the concentrations tested ranging from pCl 1 (log[Cl − ]=−1 ) to pCl 5 (log[Cl − ]=−5 ), a very high-sensing linearity (99.23% and 99.08%) of the two types of EGFET-based Cl − microsensors is achieved. However, the sensitivity of the rectangular-channel EGFET-based Cl − microsensor (45 mV/pCl ) is much higher than that of the annular-channel EGFET-based Cl − microsensor (37 mV/pCl ). The selectivity coefficient of the investigated EGFET-chloride ion sensor under four different interfering ions (OH − , F − , SO 2− 4 , and Br − ) are also measured and analyzed.

High-perfermance and low-cost ion sensitive sensor array based on self-assembled graphene

The ion sensitive sensor array (ISSA) based on layer-by-layer (LbL) self-assembled graphene presented in this paper is capable of detecting different ions selectively with advantages of high sensing performance and low cost due to graphene inherent properties and self-assembly technique. According to the conductance change of graphene, the detection limit of ISSA is down to 1μM, much better than one dimensional carbon nanotube (CNT) sensors. The response time of ISSA is 15s. The human sweat in vitro testing also confirms the high performance of ISSA.

Low-voltage transparent SnO2 nanowire transistors gated by microporous SiO2 solid-electrolyte with improved polarization response

Low-voltage transparent SnO2 nanowire transistors gated by microporous SiO2 solid-electrolyte are fabricated using a nickel grid as a shadow mask. The operating voltage is found to be as low as 1.5 V due to the large gate capacitance (∼2 μF cm−2) related to the mobile ions-induced electric-double layer (EDL) effect. The polarization mechanism of microporous SiO2 solid electrolytes is studied and three polarizations (EDL formation, ionic migration, and dipole relaxation) at different frequencies are identified. The polarization response is optimized and the improved specific capacitance is 1 μF cm−2 at 1 kHz. The field-effect mobility, current on/off ratio and subthreshold swing are estimated to be 175 cm2 V−1 s−1, 105, and 116 mV/decade, respectively. The static and dynamic bias stress measurements indicate that transparent SnO2 nanowire FETs can operate at low-voltage with highly reproducibility. Such high-performance, low-voltage SnO2 nanowire transistors hold promise for novel device applications, such as portable ion-sensitive sensors.

Flexible pentacene ion sensitive field effect transistor with a hydrogenated silicon nitride surface treated Parylene top gate insulator

We report on the realization of flexible ion sensitive organic field effect transistors based on pentacene on which Parylene-C was deposited as top gate dielectric. In order to create proton sensitive sites at the insulator/electrolyte interface, Parylene-C surface has been covered with a thin layer of hydrogenated silicon nitride (SiN:H) deposited by photochemical vapor deposition at moderate temperature. The combination of Parylene and SiN:H enables the realization of highly reproducible and good performance transistors as well as ion sensitive sensors with an excellent pH response both in the acidic and alkaline pH range in a nearly all plastic technology.

Quaternary Alkylammonium and Alkylphosphonium Pertechnetates: Application toPertechnetate Ion-Selective Electrodes

Quaternary alkylammonium and phosphonium salts are widely used for preparation of the membranes giving a response to different ions. The selectivity of ion determination depends on hydratation energy of ion and on the nature of membrane solvent. With this approach to a creation of new ion-sensitive sensors some electrode membranes for different anions and acidocomplexes determination have been developed. But only one pertechnetate selective electrode was described earlier. However, this liquid membrane electrode has not enough high selectivity and contains concentrated radioactive solution (10 M KTcO4). Thus, it can not be widely used in the analysis of the pertecnetate solutions. The object of present work is a development and an investigation of new ion-selective electrodes for TcO4 determination.

Application of ion-sensitive sensors in water quality monitoring

Within the last years a trend towards in-situ monitoring can be observed, i.e. most new sensors for water quality monitoring are designed for direct installation in the medium, compact in size and use measurement principles which minimise maintenance demand. Ion-sensitive sensors (Ion-Sensitive-Electrode--ISE) are based on a well known measurement principle and recently some manufacturers have released probe types which are specially adapted for application in water quality monitoring. The function principle of ISE-sensors, their advantages, limitations and the different methods for sensor calibration are described. Experiences with ISE-sensors from applications in sewer networks, at different sampling points within wastewater treatment plants and for surface water monitoring are reported. An estimation of investment and operation costs in comparison to other sensor types is given.

Stimulus-sensitive hydrogels and their applications in chemical (micro)analysis.

In this tutorial review the use of stimulus-sensitive hydrogels as sensors and actuators for (micro)analytical applications is discussed. The first part of the article is aimed at making the reader familiar with stimulus-sensitive hydrogels, their chemical composition and their chemo-physical behavior. The prior art in the field, that comprises a number of sensors ranging from metal ion-sensitive sensors to antigen-sensitive sensors and a few actuators, is also treated in this part. The second part of the article focusses on the use of stimulus-sensitive hydrogels for microsensors and microactuators as well as their application in micro total analysis systems. The benefits of stimulus-sensitive hydrogels, their miniaturisation and the use of 365 nm UV-photolithography as a fast economical manufacturing technique are discussed.

Optical and electrochemical studies of thiacalix[4]arene film supported on Si/SiO 2 for ion-sensitive sensor

The present work is motivated by the development of ion-sensitive sensors (suited for aqueous medium) based on functional supported thin film as sensitive membrane. Thin thiacalix[4]arene films was deposited using the technique of thermal evaporation under vacuum to fabricate chemical ion-sensitive field effect transistor (ISFET) microsensors. The aim is to characterize thiacalix[4]arene thin film (morphology, chemical composition) and its optical and electrical properties before and after detection of copper(II) ions.

Ellipsometry measurements and impedance spectroscopy on Langmuir–Blodgett membranes on Si/SiO 2 for ion sensitive sensor

LB films containing butyrylcholinestrase (BuChE) are fabricated to realize an ion-sensitive field-effect transistor (ISFET) for the detection of organophosphorus pesticides in water. A common pesticide known as trichlorfon is examined in our work. Adsorbing the enzyme molecules onto stearylamine monolayer using the electrostatic force forms the BuChE-immobilised Langmuir–Blodgett (LB) films. Enzyme/stearylamine mixed LB films are immobilized onto ISFET and treated by glutaraldehyde vapor to improve the LB film’s stability. Two techniques, the ellipsomerty and spectroscopy methods, have been used to investigate the homogeneity and stability of these films. In ellipsometry the refractive index and thickness of Si/SiO 2/LB films are measured. By utilizing the spectroscopy technique the impedance spectrum of Si/SiO 2 and Si/SiO 2/LB films are obtained and compared to ellipsometry results.

Surface Functionalization of Ceramic Nanoparticles: Application to Ion-Sensing and Gas-Sensing Devices

AbstractThe consequences of surface functionalization by grafting molecules like hydroxysilane, chlorosilane, and hexamethyldisilazane (HMDS) are reviewed for different types of nanoparticles including Si3N4, TiO2, and SnO2. Fourier transform infrared spectrometry is used as primary investigation tool. In terms of physical properties, these surface chemical modifications lead to improvements of the ion-sensitive FET and gas sensors characteristics. The beneficial effect of hydroxy- and chlorosilane grafted on Si3N4 used as ion sensitive membranes will be demonstrated. Then, the reduction of humidity effects on HMDS-grafted TiO2 and SnO2 nanosized powders used for screen-printed CO sensors will be reported.

Aliphatic polyurethane as a matrix for pH sensors: effects of native sites and added proton carrier on electrical and potentiometric properties

The potentiometric and impedance characteristics of polymeric membranes, based on aliphatic polyurethane (Tecoflex) as a matrix, are described and interpreted by theory and experiments for H + and alkali metal ion-sensitive sensors. Both dummy plasticized membranes and proton carrier-loaded membranes can show pH response. The pH response of dummy membranes is due to protonated natural negative sites in the polyurethane matrix. The electrodes with added proton carrier show improved rejection of Li +, Na +, and K + responses and give useful analytical responses. Optimal performance requires control of negative site concentration by addition of lipophilic salt (e.g. tetraphenylborate derivatives). Impedance analyses show surface-rate semicircles and, depending on the bathing electrolyte solution, appearance of a diffusional Warburg impedance. In addition to these time-dependence surface region effects, changes in the bulk membrane resistance with soaking time can be well correlated with equilibrium water content of plasticized membranes.