Potassium ion-sensitive field effect transistors using valinomycin doped photoresist membrane

Conclusion The potassium ion-sensitive membrane, prepared by the inclusion of valinomycin and plasticizer into the photoresist proved to be a good potassium ion-sensitive membrane for the ISFET. The plasticizer was found to play an important role in the photoresist membrane to obtain potassium ion-sensitivity. The plasticizer photoresist membrane showed not only more sensitivity but also longer term stability than the plasticized PVC membrane. It is concluded that the plasticized photoresist membrane deposited at the gate region of the ISFET works satisfactory for the determination of potassium ion activity in aqueous solution.

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Kalium-ionensensitive Feldeffekt-Transistoren mit Valinomycin-dotierten photoresistenten Membranen

     

Potentiometric response of lipid modified ISFET

The gate surface of an ion-sensitive field effect transistor (ISFET) was modified with Langmuir-Blodgett (LB) film composed of fatty acid or crown ether amphiphiles to examine their potentiometric response to H⁺ and K⁺ ions. The results demonstrate the possible use of the lipid films for preparing ISFET ion sensors.     

Detecting Both Physical and (Bio‐)Chemical Parameters by Means of ISFET Devices

A multi‐parameter sensor system for the detection of eight (bio‐)chemical and physical parameters (pH, potassium concentration, penicillin concentration, diffusion coefficient of H⁺‐ and OH ^–‐ions, temperature, flow velocity, flow direction and liquid level) is realized by using the same transducer principle. A Ta₂O₅‐gate ISFET (ion‐sensitive field‐effect transistor) is applied as basic transducer for all kinds of sensors. The multi‐parameter detection is achieved by means of sequentially or simultaneously scheduling of the hybride sensor modules consisting of four ISFET structures and an ion generator in different sensor arrangements and/or different operation modes. Thus, more parameters (eight) can be detected than the number of sensors (four) in the system.     

Ion-sensitive field effect transistors using carbon nanotubes as the transducing layer

We report a new type of ion-sensitive field effect transistor (ISFET). This type of ISFET incorporates a new architecture, containing a network of single-walled carbon nanotubes (SWCNTs) as the transduction layer, making an external reference electrode unnecessary. To show an example of its application, the SWCNT-based ISFET is able to detect at least 10(-8) M of potassium in water using an ion-selective membrane containing valinomycin.     

Analysis and identification of several apple varieties using ISFETs sensors

There are a number of variables that are useful to determine the optimal moment for the fruit collection such as starch content, sugar content, acidity and firmness. Other variables, including calcium and potassium concentrations, may establish better the state of ripeness of fruit and can help to optimise the collection process as well as augmenting the nutritional value of fruits. At present, these novel parameters cannot be used for the control of fruit collection due to the slow standard methods required. The need for in situ and in real-time ion measurements calls for fast response sensors and simpler and portable instrumentation. Solid-state sensors respond to these requirements. This work describes the application of ISFET sensors to analyse calcium, potassium and nitrates in several apple varieties, both in juice and in situ fruit. Results show that the analysis of potassium, calcium and nitrate permits to distinguish among apple varieties and can also be used to determine correctly the concentrations of these ions.     

Development of microbiosensors

Semiconductor fabrication technology was used for development of ion sensitive field effect transistor (ISFET) and micro-electrodes which have been utilized as transducers of enzyme-based microbiosensors. A urea sensor consisted of two ISFETs; one ISFET is urease-coated ISFET and the other ISFET is reference ISFET. A linear relationship was obtained between the initial rate of voltage change and the logarithm of urea concentration over the range 1.3 to 16.7 mM. ATP and hypoxanthine sensors were also developed utilizing ISFET as a transducer. Furthermore, microelectrodes such as hydrogen peroxide and oxygen sensors were prepared by the silicone fabrication technology. A glucose sensor consisted of a hydrogen peroxide electrode and immobilized glucose oxidase membrane. A linear relationship was observed between the current increase and the concentration of glucose (1–100 mg dl⁻¹). A microoxygen electrode was constructed from Au electrodes, polymer matrix containing alkaline electrolyte and a photocross-linkable polymer membrane. This electrode was used as a transducer in microglucose sensor. A microglutamic acid sensor is also described.     

Alcohol-FET sensor based on a complex cell membrane enzyme system

An alcohol -FET sensor was developed by use of a complex enzyme system in a cell membrane and an ion-sensitive field effect transistor (ISFET). The cell membrane of Gluconobacter suboxydans IFO 12528, which converts ethanol to acetic acid, was immobilized on the gate of an ISFET with calcium alginate gel coated with nitrocellulose. This ISFET (1), a reference ISFET without the cell membrane (ISFET 2) and an Ag/AgCl reference electrode were placed in 5 mM Trismalate buffer (pH 5.5, 25°C), and the differential output between ISFETS 1 and 2 was measured. The output of the sensor was stabilized by adding pyrroloquinoline quinone. The response time was ca. 10 min., and there was a linear relationship between the differential output voltage and the ethanol concentration up to 20 mg l^?1. The output of the sensor was stable for 40 h below 30°C. The sensor responded to ethanol, propan- 1-ol and butan- 1-ol, but not to methanol, propan-2-ol and butan-2-ol. The sensor was used to determine blood ethanol.     

A novel Urushi matrix chloride ion-selective field effect transistor

A durable chloride ion-selective field effect transistor (ISFET) is proposed with Urushi as the membrane matrix. The chloride ion-sensing material is a quaternary ammonium chloride: trioctylmethylammonium chloride (TOMA-Cl) or tridodecylmethylammonium chloride (TDMA-Cl). The optimum composition of the Urushi membrane was found by use of Urushi ion-selective electrodes. The mixture with the most favourable composition was coated on the gate region of the FET device. The Urushi ISFET with TDMA-Cl proved to be superior to that with TOMA-Cl, in sensitivity, linearity and selectivity. The Urushi ISFET with TDMA-Cl showed a linear response of about -51 mV per decade change of chloride ion activity in the range 10(-4)-1M. The Urushi ISFET showed excellent stability and durability for over two months, because of strong adhesion of the membrane to the Si(3)N(4) gate.     

Characterization of the Analytical Response of ISFET Sensors for Quantitative and Thermodynamic Assessment in Glacial Acetic Acid

This work presents the results of the studies on the operating characteristics of ISFET sensors, which had a silicon nitride membrane, using glacial acetic acid as solvent. The stability periods found were between five and seven minutes with response time in the range of 50 to 70 seconds. Pyridine was determined quantitatively and the results were compared with those obtained with a commercial glass electrode; the analysis of variance (ANOVA) demonstrated that there were no significant differences for the results from either type of sensor. The Biederman and Sillén calibration method was applied to the potentiometric system: the linear response range found was 4.3<pH<10.4. The ISFET presented different sensitivities for the acid and basic regions, such that with usage the sensitivity increased toward the acetate ion while that for the solvated proton decreased, and so did the reproducibility as well. The initial analytical properties of the sensor are restored upon regeneration of the silicon nitride membrane. The equilibrium constants for the protonated pyridine and diethylamine perchlorates were determined: the values found do not differ statistically in respect to those reported in the literature. Also, it was found that upon regeneration of the selective membrane, the ISFET can be used in aqueous and glacial acetic media.     

Acetylcholine Sensor Based on Ion Sensitive Field Effect Transistor and Acetylcholine Receptor

Abstract

A new type of acetylcholine sensor was made with an Ion Sensitive Field Effect Transistor (ISFET) and acetylcholine receptor. The acetylcholine receptor was fixed on a polyvinylbutyral membrane which covered the ISFET gate. When acetylcholine was injected into this system, the differential gate output voltage gradually Shifted to the positive side and reached a constant value. This response was due to the positive charge of acetylcholine. A linear relationship was obtained between the initial rate of the differential gate output voltage change and the logarithmic value of the acetylcholine concentration. Acetylcholine was fixed in the range 0.1-10μM. When the acetylcholine receptor was immobilized with the lipid membrane, the response was amplified with both the positive charge of acetylcholine and sodium ion flux through the acetylcholine receptor's channel. Therefore, the difference in the differential voltage between the acetylcholine receptor-ISFET systems with and without the lipid membrane was caused by sodium ion flux through the acetylcholine receptor's channel.     

Enzymatic determination of urea in undiluted whole blood by flow injection analysis using an ammonium ion-selective electrode

A flow-injection system is described for the assay of urea in undiluted whole blood. Urea is quantified by means of an ammonium ion-selective electrode covered with a membrane with covalently immobilized urease. The enzymatically generated ammonium ion is directly related to the urea concentration. Interference from potassium is reduced by adjusting the potassium ion concentration in the carrier stream and in the aqueous calibration solutions to 4.0 mM; it can be eliminated by measuring the potassium ion concentration in the sample separately and applying a mathematical correction for the K⁺ contribution to the signal. The linear measuring range is 1–40 mM urea, with an injection frequency of 40 h^?1 and a standard deviation of 1% for whole blood samples. The result of the measurement is obtained within 25 s from the time of injection. Vatiations in the hematocrit level of the sample have no effect on the measurement. The results obtained by the flow-injection method are in excellent agreement with those found routinely at a local hospital. The sensor is stable for more than 25 days.     

Immobilization of E. coli bacteria in three-dimensional matrices for ISFET biosensor design

In recent years, cell-based biosensors (CBBs) have been very useful in biomedicine, food industry, environmental monitoring and pharmaceutical screening. They constitute an economical substitute for enzymatic biosensors, but cell immobilization remains a limitation in this technology. To investigate into the potential applications of cell-based biosensors, we describe an electrochemical system based on a microbial biosensor using an Escherichia coli K-12 derivative as a primary transducer to detect biologically active agents. pH variations were recorded by an ion-sensitive field effect transistor (ISFET) sensor on bacteria immobilized in agarose gels. The ISFET device was directly introduced in 100 ml of this mixture or in a miniaturized system using a dialysis membrane that contains 1 ml of the same mixture. The bacterial activity could be detected for several days. The extracellular acidification rate (ECAR) was analyzed with or without the addition of a culture medium or an antibiotic solution. At first, the microorganisms acidified their micro-environment and then they alkalinized it. These two phases were attributed to an apparent substrate preference of bacteria. Cell treatment with an inhibitor or an activator of their metabolism was then monitored and streptomycin effect was tested.     

Ion-selective field effect transistors with polymeric membranes

The construction and operation of ion-selective field effect transistors (ISFET) with polymeric membranes are described, and their electrical and chemical performance are discussed. The H⁺, K⁺, and Ca²⁺ ISFET's all show responses similar to those of the corresponding ion-selective electrodes, with t_95% response times of approximately 40 ms and accurate ion activity measurements for periods up to one month.     

Neutral-carrier-type potassium ion-selective electrodes based on polymer-supported liquid-crystal membranes for practical use.

Polymer-supported liquid-crystal membranes have been designed for neutral-carrier-type potassium ion-selective electrodes, aiming for practical applications of high-performance liquid-crystalline membrane ion sensors. Two types of polymer-supported liquid-crystal membranes were tested for their usefulness; one is microporous poly(tetra fluoroethylene) (PTFE) membranes impregnated by thermotropic liquid-crystalline compounds, and another is poly(methyl methacrylate) (PMMA) membrane dispersing the same liquid-crystalline compounds. Both of the polymer-supported liquid-crystal membranes containing a liquid-crystalline benzo-15-crown-5 neutral carrier as well as a lipophilic anion excluder work well as ion-sensing membranes for potassium ion-selective electrodes, the ion selectivities of which can be switched by the measurement temperatures. Specifically, PTFE-impregnated liquid-crystal membranes are better than the PMMA-dispersed ones in the sensitivity and selectivity of the resulting ion electrodes. A potassium ion assay in blood sera has proved that neutral-carrier-type ion-selective electrodes based on the polymer-supported liquid-crystal membranes are reliable for practical uses.     

Enzyme sensors based on an ion-sensitive field effect transistor coated with Langmuir-Blodgett membranes. Use of polyethyleneimine as a spacer for immobilizing alpha-chymotrypsin

A highly branched polyethyleneimine (PEI) was used as a spacer for immobilizing alpha-chymotrypsin on the surface of Langmuir-Blodgett (LB) membranes which were deposited on the gate of an ion-sensitive field effect transistor (ISFET). alpha-Chymotrypsin could be covalently immobilized through the glutaraldehyde-activated PEI on the LB membrane-coated ISFET. The alpha-chymotrypsin-modified ISFET showed a potentiometric response to the substrate at concentrations of more than 0.1 mM. Some performance characteristics of the sensor, such as pH response, response time, and long-term stability were examined.     

Highly Selective Ion-Sensitive Electrodes Based on Dibenzo-Crown Ethers Containing Functional Groups for the Determination of Potassium in Biological Fluids

The electrochemical properties of membranes based on dibenzo-crown ethers bearing hydroxyl and chloromethyl groups in polyether rings were studied. These substances were tested as membrane ionophores for ion-selective electrodes (ISEs) reversible to potassium ion. The developed ISEs were used for determining potassium in blood plasma samples. The generalized results of determining potassium in the blood of different patients with cardiovascular diseases revealed quantitative regularities that allowed the diseases to be diagnosed early.     

Potassium ion-selective electrodes based on valinomycin/PVC overlayered solid substrates

In this work, permutations of plasticized PVC membranes with incorporated valinomycin are coated over various substrate metallizations. Characterization of the resulting potassium electrodes includes measurement of sensitivity, short- and long-term potential drift, dissolved oxygen induced potential transients and probe lifetime. Results using the best performing metallizations compare favorably with those obtained using identical membranes in the symmetrical solution contact configuration. Prospects for use of this approach as the ion-sensing layer of ISFET (Ion-Sensitive Field-Effect Transistor) devices are considered.     

Chemfet Based Microsensors Covered with Ion-Partitioning Polymeric Membranes

 The development of a new type of microsensors based on chemically sensitive field-effect transistors (CHEMFETs) covered with polymeric bulk ion-partitioning membranes is presented. For the construction of the microsensor, a PVC plasticized membrane containing two ionophores, one selective to protons and the other to the analyte cation of interest, is placed on the gate of a pH sensitive field-effect transistor which acts as the transducer. With the use of thin (5–10 μm) ion-partitioning membranes onto the pH-sensitive ISFET gate, the proton displacement out of the membrane and to the pH sensitive gate is fast and reversible. This displacement generates a signal that is directly related to the analyte concentration found in the test solution. Comparing the performance of CHEMFETs and ISEs selective to the monovalent potassium cation and the divalent calcium ion validates this novel CHEMFET response mechanism.     

Enzyme-based field-effect transistor for adenosine triphosphate (ATP) sensing.

Adenosine triphosphate (ATP) not only functions as an energy-carrier substance and an informative molecule, but also acts as a marker substance in studies of both bio-traces and cellular/tissular viability. Due to the importance of the ATP function for living organisms, in situ assays of ATP are in demand in various fields, e.g., hygiene. In the present study, we developed an ATP sensor that combines the selective catalytic activity of enzyme and the properties of an ion selective field effect transistor (ISFET). In this system, the ATP hydrolyrase, "apyrase (EC 3.6.1.5.)" is encased in a gel and mounted on a Ta(2)O(5) ISFET gate surface. When the enzyme layer selectively catalyzes the dephosphorylation of ATP, protons are accumulated at the gate because the enzymatic reaction produces H(+) as a byproduct. Based on the interfacial enzymatic reaction, the response from the ISFET is completely dependent upon the ATP concentration in the bulk solution. This device is readily applicable to practical in situ ATP measurement, e.g. hygienic usage.