Ion-selective Field Effect Transistor Research Articles

An Analytical Technique for Counteracting Drift in Ion-Selective Field Effect Transistors (ISFETs)

The instability of the dc operating point in pH-sensitive ion-selective field effect transistors (ISFETs) renders the continuous monitoring of physiological pH using these devices inaccurate. This instability, commonly known as drift, manifests itself as a relatively slow, monotonic change in the measuring output signal in the absence of variations in the pH. In this work, a method for correction of ISFET drift is presented. This method takes advantage of the relatively small instantaneous drift rate in ISFETs to compensate for the drift signal superimposed on the sensor output. The validity of this method is experimentally confirmed by continuous monitoring of pH under in vitro conditions approximating metabolic acidosis using a Si/sub 3/N/sub 4/-gate pH-sensitive ISFET.

ISFET interface circuit embedded with noise rejection capability

A new constant-current voltage driver forms a bridge-type floating drain-source follower configuration applicable to the determination of H+ ion concentration. The proposed circuit maintains the ion-selective field effect transistor (ISFET) in an accurate constant drain-source voltage and current situation with good noise rejection capability. Simulation results show accurate response for ISFET applications. The presented electronic circuit can be integrated with a ISFET-based microsystem by standard CMOS technology.

Биосенсоры на основе ионоселективных полевых транзисторов: теория, технология, практика

Биосенсоры на основе ионоселективных полевых транзисторов: теория, технология, практика

Nanostructures for chemical recognition using ISFET sensors

The application of Langmuir–Blodgett (LB)-fabricated nanostructures on Ion selective Field Effect Transistors (ISFET) is of great interest since it permits the combination of a micro-scale device with a nanoscale material. In this article, the optimization of a LB-monolayer for calcium and sodium detection is carried out by characterization with XPS and AFM techniques, followed by electrochemical characterisation onto ISFET sensors. Physico-chemical modifications of the surface and good cation complexation of the ionophores fixed in the monolayers were observed with XPS studies. AFM images showed the presence of a unhomogeneous layer all over the ISFET surface. The electrochemical response of those monolayers onto ISFETs demonstrated the feasibility of this technology for sensor membrane fabrication and it opens further studies for other kind of devices such as optochemical sensors.

Biosensors based on enzyme field-effect transistors for determination of some substrates and inhibitors.

This paper is a review of the authors' publications concerning the development of biosensors based on enzyme field-effect transistors (ENFETs) for direct substrates or inhibitors analysis. Such biosensors were designed by using immobilised enzymes and ion-selective field-effect transistors (ISFETs). Highly specific, sensitive, simple, fast and cheap determination of different substances renders them as promising tools in medicine, biotechnology, environmental control, agriculture and the food industry. The biosensors based on ENFETs and direct enzyme analysis for determination of concentrations of different substrates (glucose, urea, penicillin, formaldehyde, creatinine, etc.) have been developed and their laboratory prototypes were fabricated. Improvement of the analytical characteristics of such biosensors may be achieved by using a differential mode of measurement, working solutions with different buffer concentrations and specific agents, negatively or positively charged additional membranes, or genetically modified enzymes. These approaches allow one to decrease the effect of the buffer capacity influence on the sensor response in an aim to increase the sensitivity of the biosensors and to extend their dynamic ranges. Biosensors for the determination of concentrations of different toxic substances (organophosphorous pesticides, heavy metal ions, hypochlorite, glycoalkaloids, etc.) were designed on the basis of reversible and/or irreversible enzyme inhibition effect(s). The conception of an enzymatic multibiosensor for the determination of different toxic substances based on the enzyme inhibition effect is also described. We will discuss the respective advantages and disadvantages of biosensors based on the ENFETs developed and also demonstrate their practical application.

Iridium oxide sensors for acidity and basicity detection in industrial lubricants

The lubrication and automotive industries are seeking on-line sensors capable of determining the chemical condition and degree of degradation of industrial and automotive lubricants in order to signal the need for an oil change. Levels of acidity and basicity in non-aqueous media are parameters common to a wide variety of industrial fluids and closely related to rate of the lubricant oxidation breakdown. Therefore, development of chemical devices capable of continuous monitoring of these parameters remains an important goal of industrial sensor research. Chronopotentiometric (CP) sensors based on solid-state reversible oxide films of iridium demonstrate a number of advantages for detection of acidity and basicity levels in non-aqueous industrial lubricants over other types of acidity sensors, such as glass electrode and ion-selective field effect transistors. Iridium oxide sensors fabricated by different methods and having various geometric configurations (macro-scale versus microelectromechanical systems (MEMS)) were compared. The sensors demonstrated linear responses to changes in oil acidity and basicity that were in agreement with proposed electrochemical mechanisms. Studies of long term stability and durability of the metal oxide sensors in the oil solutions illustrated that improvement to the sensor fabrication process is needed.

Comparison of Urea Determination in Biological Samples by EnFETs Based on pH and pNH4 Detection

In this paper urea biosensors based on detection of pH and ammonium ions are presented. As transducers pH-sensitive ion-selective field effect transistors (ISFETs) and chemically modified FETs (ChemFETs) snsitive to ammonium ions were used.Results concerning urea determination by the bisensors in blood plasma and in dialysate show that the biosensors can be applied for urea monitoring in the effluent dialysate. However in the case of pNH4 based EnFETs a special pre-treatment (dilution with tris/HCl buffer) of the samples is necessary.

Analytical characteristics and sensitivity mechanisms of electrolyte-insulator-semiconductor system-based chemical sensors-a critical review.

Recent trends in research and development of electrolyte-insulator-semiconductor (EIS) field-effect chemical sensors (ion-selective field-effect transistors, light-addressable potentiometric sensors, capacitive EIS-sensors) with inorganic gate insulators (oxide, nitride and chalcogenide films) are reviewed. Physical properties of EIS systems and basic mechanisms of their chemical sensitivity are examined. Analytical characteristics and sensing mechanisms of EIS pH sensors with oxide and nitride films, as well as metal ions sensors with chalcogenide films, are critically discussed. Prospects of future research on EIS field-effect biosensors are briefly outlined.

Portable urea biosensor based on the extended-gate field effect transistor

In this study, extended-gate field effect transistor (EGFET) was applied to fabricate disposable urea biosensor. And the 1.5 V low-voltage instrument amplifier was adopted to realize the portable urea biosensor. However, the difference between extended-gate field effect transistor and traditional ion-selective field effect transistor is the position of the sensitive membrane. The extended-gate field effect transistor was separated into two parts, which are the sensitive membrane and MOSFET. Hence, the MOSFET device can be designed to be a part of the readout circuit and the sensitive membrane was only put in the solution. Therefore, the configuration of the extended-gate field effect transistor can reduce the influence of the temperature, light and the erosion by the solutions. Besides, the configuration can reduce the cost substantially. The configuration of the extended-gate field effect transistor will raise the competitiveness to develop the disposable biosensor. The content of the urea in blood is one of the indexes to diagnose the renal efficiency. Then, the portable urea biosensor is the important expandable aspect. In this study, the gels, which are the poly vinyl alcohol with pendent styrylpyridinium groups, were used to immobilize the urease. The detection of the urea is based on the variation of pH value. Then, the dynamic range of the urea biosensor is from 0.31 to 120 mg/dl at the 5 mM phosphate buffer solution and the response time is about 2 min.

Development of a multiparametric analyser based on ISFET sensors applied to process control in the wine industry

The continuous monitoring of processes in the food industry, and in particular in wine production, holds great interest as it can help to increase the quality of the goods produced and also the efficiency of the production process. One process that is feasible to control is the stabilisation of wine by means of ion-exchange resins. The use of this technique is of great promise since it allows continuous wine treatment and also on-line monitoring systems can be applied to determine the saturation of the resin in addition to the fraction of wine requiring stabilisation. The development of a pH, calcium and potassium analyser for on-line monitoring of wine in a continuous flow system is reported here. The potentiometric sensors used are ion-selective field-effect transistors (ISFETs). The stability of these sensors in hydro-alcoholic media was studied obtaining a sensitivity of 56 mV per decade for the pH ISFET and sensitivities of −26 mV per decade and −50 mV per decade for calcium and potassium sensors, respectively. The long-term stability of pH-ISFETs was 7 and 4 months for cation sensors. Results obtained in the continuous flow system with wine samples demonstrated that the proposed system is capable to detect the saturation point of the ion-exchange resin in wine stabilisation process and also to determine the ratio of wine required to stabilise it.

Design and performance of some microflow-cell potentiometric transducers.

The paper presents and compares the design of three potentiometric transducers: ion-selective field effect transistor (ISFET), solid-state Ag/AgCl electrode and miniaturized classical Ag/AgCl electrode. The reported transducers were fabricated using different, less or more complicated and expensive, technologies. The transducers were constructed to be compatible with the sensor housing of the flow-cell, designed previously. Moreover, the back-side contact structures of the two planar devices, where electrical connectors and the sensing layer are on the opposite sides, facilitated their application in the flow analysis. Exemplary potassium-selective microsensors based on developed transducers were prepared, applying plasticized PVC and polysiloxane membranes containing valinomycine. The determined microsensor performances allowed comparison of their usefulness for multiparameter flow analysis.

Effect of the Surface Pretreatment on the Electrokinetic Properties of Silicon and Silicon Oxide

The electrokinetic characteristics (the isoelectric point, electrokinetic potential, and surface conductivity) are studied as functions of pH against the background of NaCl solutions for the initial surfaces of silicon (covered with an oxide layer) and silicon oxide (a plane-parallel capillary of quartz glass and aerosil OX-50) and for the same surfaces after a preliminary thermal and chemical (CCl4 vapors at 400°C) treatment. The position of the isoelectric point for the systems in question is shown to be primarily affected by the preliminary annealing, which shifts this point toward higher pH. The electrokinetic behavior of silicon plates covered with an oxide film is compared to the electrode behavior of a similar board of an ion-selective field-effect transistor.

Determination of the diffusion coefficient of proton in CVD gamma aluminum oxide thin films

Proton diffusion in aluminum oxide thin films is of significant interest because of its importance in barrier, sensor and catalytic coating applications. In this study, a novel method based on potential-pH response measurement was used to determine proton diffusivity in CVD produced gamma aluminum oxide thin films. This technique based on the model of diffusion-controlled transport at the oxide surface, measures the potential-pH response drift as a stepwise increase and decrease in pH (i.e. pH 4 and 7) with a thermostatic measurement set-up. The drift in the potential-pH response is believed to be due to the surface layer, which affects proton diffusion onto the oxide film of the Al 2O 3-gate ion selective field effect transistor. The diffusion coefficient of proton in aluminum oxide thin film using the potential-pH response method was 6.5×10 −18 cm 2/s. The unique feature of this method is its relatively simple experimental procedure, which eliminates complications arising from surface related effects and/or presence of hydrogen traps in the metal, also offers a considerable reduction in test time with the experiment being completed in 10 h as compared to the conventional electrochemical permeation method which takes as long as 5 days.

The Potentiometric Biosensor Acetylcholine Esterase as a Model System

In a methodical investigation of pH-detection systems (glass and polymer membrane electrodes and ion selective field effect transistor (ISFET)), the possible use of the acetylcholine esterase biosensor as a model for all pH-based biosensors is shown. It revealed that the biomembrane properties are more important for the result than the technology itself. All techniques resulted in a ΔH+ detection limit of 6*10−7 mol/L.

Reducing the interference from CO 2 or organic acids in ion-selective polymer membrane sensors having a field-effect transistor as internal reference element

Changes in sample concentrations of CO 2 or organic acids cause potential instabilities when polymer membranes are directly applied to the surface of ion-selective field-effect transistors (ISFETs). Currently used designs avoid this well-documented effect by placing a layer of aqueous buffer between polymeric membrane and ISFET serving as internal reference element. Here, we propose another solution to the problem. In order to compensate for the effect of pH changes on the ISFET threshold voltage, a double membrane is applied whose inner layer is pH-sensitive, while the outer layer exposed to the sample is a conventional ion-selective membrane. It is shown that this approach strongly reduces the earlier-mentioned interference effects.

Continuous monitoring of gastric intraluminal carbon dioxide pressure, cardiac output, and end-tidal carbon dioxide pressure in the perioperative period in patients receiving cardiovascular surgery using cardiopulmonary bypass.

To verify the hypothesis that the gastric intraluminal PCO2 (PgCO2) changes independently of the change in cardiac output (CO) during and after cardiovascular surgery using cardiopulmonary bypass (CPB), and that the elevation of PgCO2 affects the patients' morbidity. Prospective, noninterventional study. Medical/surgical intensive care unit and operating theater of a university hospital. Sixteen adults patients receiving elective cardiovascular surgery using CPB. None. After induction of anesthesia, the patients were fitted with a gastric tube equipped at the tip with a CO2 sensor (ion-selective field effect transistor) that can continuously measure real-time PgCO2, and a pulmonary artery catheter capable of monitoring continuous CO (CCO) and end-tidal CO2. Data from the devices was uploaded to a personal computer every 2 mins until the catheter was pulled off based on clinical judgment (PgCO2 values were blinded to everyone except the investigator). One patient expired as a result of multiple organ failure subsequent to sepsis, and postoperative morbidity assessed by the peak SOFA (sequential organ failure assessment) score (mean +/- SD 6.9 +/- 3.5; range, 2-13) was correlated with the peak PgCO2 during intensive care unit stay (mean +/- SD 74.1 +/- 30.7 mm Hg; range, 45-169 mm Hg) (p < .01, by regression analysis). The peak PgCO2 during surgery (mean +/- SD 71.1 +/- 18.1 mm Hg; range, 44-115 mm Hg) had no correlation with the postoperative morbidity. From analysis of CCO before, during, and after returning from the above 60 mm Hg of PgCO2, PgCO2 changed independently of CCO. PgCO2 changed independently of CCO, and its postoperative elevation was related to morbidity, even in the group of patients with a good outcome. Continuous monitoring of PgCO2 is useful for the detection of morbidity and can be expected to help elucidate the pathophysiology of change of PgCO2.

Improved potassium-selective membrane using valinomycin as ionophore for ion-selective microdevices

Ion-selective field effect transistors (ISFETs) were tested for their suitability for clinical work. They were intended for use in the analysis of blood and serum, where the concentration of specific ions, e.g. sodium and potassium, is of critical importance. The optical sensitivity of ISFETs and a new membrane composition for use in the clinical chemistry were evaluated. ISFETs with a polyimide/valinomycin membrane were shown to operate satisfactorily in the presence of proteins, encouraging the further development of these ISFETs as clinical sensors. ETH 2041 (tetra- n-undecyl 3,3′, 4,4′–benzophenone tetracarboxylate) and DGD (diethylene dibenzoate) were the plasticizers used and their performances were compared. Valinomycin was used as ionophore. The membranes were calibrated using the dip (solutions in the 10 −1–10 −5 mol dm −3 KCl range) and the constant volume dilution methods. Both membrane compositions gave good Nernstian responses. The ETH 2041 plasticizer was found to yield devices more selective to potassium ion than the more easily usable DGD.

Photocurable ISFET for anionic surfactants. Monitoring of photodegradation processes

The preparation of a new ion-selective field-effect transistor (ISFET) based on a photocurable membrane sensitive to anionic surfactants is described. The membrane is formed by an urethane–acrylate matrix with 2-cyanophenyl octyl ether as the plasticiser. When compared to conventional ion-selective electrodes, the prepared ISFETs do not show significant differences in sensitivity and reproducibility ( P=0.05). When calibrating with dodecylbenzenesulfonate (DBS −) the prepared ISFETs show a nernstian behaviour, with a slope of 57.5 mV per decade. The linear working range is 1.0×10 −3 to 3.0×10 −6 M DBS − and the detection limit is 1.2×10 −6 M. The response times were below 0.7 min in all cases (95% of the step change). As the application, photodegradation processes using titanium dioxide dispersions, were monitored for two common anionic surfactants: DBS −, being aromatic, and the more alkylic dodecylsulfate, DS −. The determination of surfactant concentration was performed following a standard addition methodology, using ISFETs as the sensors, and without any previous separation stages. The degradation kinetics in both cases are first-order processes, with half-life times ( t 0.5) of 31.5 min for DBS − and 52.0 min for DS −.

Real-time multi ISFET/FIA soil analysis system with automatic sample extraction

Successful implementation of site-specific crop management relies on accurate quantification of spatial variation of important factors. Therefore, there is a tremendous need for the development of sensing technologies that will allow automated collection of soil, crop and pest data, to more accurately characterize within-field variability. The objective of this work was to develop an integrated multi-sensor soil analysis system. Ion-selective field effect transistor (ISFET) technology was coupled with flow injection analysis (FIA) to produce a real-time soil analysis system. Testing of the ISFET/ FIA system for soil analysis was carried out in two stages: (1) using manually extracted samples, and (2) the soil to be analysed was placed in the automated soil extraction system, and the extracted solution fed directly into the FIA system. The sensor was successful in measuring soil nitrates in manually extracted soil solutions ( r 2>0.9). The rapid response of the system allowed a sample to be analysed in 1.25 s, which is satisfactory for real-time soil sensing. Precision and accuracy of the system were highly dependent on maintaining precise, repetitive injection times and maintaining constant flow parameters during the calibration and testing cycle. The progress toward an automated soil extraction system was notable, but considerable effort will be necessary before commercialization can be realized. However, the concept of using ISFETs for the real-time analysis of soil nitrates is sound. The rapid response and low sample volumes required by the multi-sensor ISFET/FIA system make it a viable candidate for use in real-time soil nutrient sensing.

Studies on pH and Nitrate Checkers Made of Semiconductor Devices for Acid Rain Monitoring

Ion-selective field-effect transistors (ISFETs), which are integrated devices for ion-selective electrodes using solid-state microelectronics technology, have attracted much attention for convenient monitoring of acid rain, since conventional analytical procedures are time-consuming. In this paper, some recent results of studies on pH and nitrate checkers made of ISFETs using new sensing materials and their application to samples of acid rain are described.