Urea Sensor Research Articles

Thermal analysis, conducting properties and electrochemical applications of some conductor-doped polymers. Part 2

Abstract Polymers of para- and meta-diethynylbenzene and 2,6-diethynylpyridine, massively doped with iodine, were analysed by TG, DTG and DSC techniques and their conductivity values were measured. Some analytical results, obtained using a polymeric ion selective electrode (selective to NH4+) and an enzyme urea sensor, both based on a PVC membrane containing poly-para-diethynylbenzene, are also reported.

Biosensing with coated-wire electrodes. Part 2. Urea sensors

Enzyme electrodes are described for the determination of urea based on an ammonium ion-selective coated-wire electrode. The electrodes consisted of homogeneous membranes of poly(vinyl chloride)(PVC) or silicone rubber containing both the electroactive species and immobilised enzyme. Those sensors in which PVC was utilised as the membrane proved to be the most useful and for a 0.2 mm thick membrane a super-Nernstian calibration was obtained with a mean slope of 61 ± 1 mV decade–1 under static conditions of measurement. The lifetime of the electrodes was approximately 10 d. The electrode could be used in a miniaturised, custom-designed flow cell for automated analysis. In this mode the slope of the calibration obtained was 67 ± 2 mV decade–1.

Photo-switchable ion and enzyme sensors. Photoinduced potentiometric response of glassy carbon electrode coated with polymer or polymer/enzyme dual membrane.

Photo-switchable ion and enzyme sensors were fabricated by the use of glassy carbon electrode coated with nonactindoped or enzyme modified poly(vinyl chloride) (PVC) membranes. The ion sensor with nonactin-doped PVC membrane, which contained spirobenzopyran as the photosensitive dye, exhibited a potentiometric photoresponse to NH4+ ion in the solution. The dynamic range of the NH4+ ion sensor was 10(-7)--10(-3) M. Urea, adenosine, and asparagine sensors were prepared by coating the surface of the NH4+-ion sensor with urease, adenosine deaminase, and asparaginase membranes, respectively. These enzyme sensors could be used for determining the substrates at the micro mole level. The performance characteristics of these sensors were compared with those previously prepared membrane electrode sensors.

Biosensors based on conducting filled polymer all-solid-state pvc matrix membrane electrodes

Transducers consisting of PVC matrix membranes applied to conducting filled polymers and featuring no inner reference solution are proposed as viable alternatives to the construction of potentiometric biosensors. The construction procedure basically involves the application of biocatalyst layers (e.g. immobilized enzymes or whole bacterium cells) on mobilecarrier PVC membranes formed in-situ and deposited directly on a conductive plastic support which functions as an internal solid contact. The chief advantage of this construction procedure is the ease with which sensors in different shapes and sizes can be prepared. Thus this technique allows the obtainment of flow-through sensors for use in flow-injection analysis, of which those with sandwich configuration are particularly suitable for the construction of flow-through electrochemical biosensors. The results obtained with various potentiometric urea sensors in different configurations and based on all-solid-state ammonium-selective electrodes constructed by the proposed technique are reported.

Ion Sensitivity of Fe3O4 Film Prepared by Ferrite Plating and Its Application to Urea Sensor

Ion Sensitivity of Fe₃O₄ Film Prepared by Ferrite Plating and Its Application to Urea Sensor

An integrated multibiosensor for simultaneous amperometric and potentiometric measurement

A multibiosensor, in which a glucose sensor based on amperometry and a urea sensor based on potentiometry are integrated, has been realized by complementary use of ISFETs and micro-patterned planar gold electrodes. This multibiosensor is composed of two ISFETs and three micro-planar gold electrodes on a silicon on sapphire (SOS) device. On the back surface gold layer, one of the electrodes works both as a counter electrode for the amperometric measurement, and as a pseudo reference electrode for the potentiometric measurement. Glucose oxidase (GOD)-immobilized membrane, urease-immobilized membrane, and bovine serum albumin (BSA) crosslinking membranes were deposited in appropriate positions by a lift-off method, one of the integrated circuit (IC) fabrication processes. Consequently the multibiosensor is very suitable for miniaturization and mass production. A glucose concentration in the range 1 to 100 mg/dl and a urea concentration in the range 5 to 100 mg/dl were measured with a good relationship. In the multibiosensor, amperometry and potentiometry exist on a complementary basis and each process provides what the other needs. The multibiosensor can thus be called a ‘complementary multibiosensor (COMBIS)’.

A Novel Amperometric Urea Sensor

A Novel Amperometric Urea Sensor

Development of microbiosensors

AbstractSemiconductor 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.

Flow injection analysis as a diagnostic technique for development and testing of chemical sensors

An immobilized urease sensor is developed for continuous, on-line analysis. The sensor consists of the enzyme urease, cross-linked with bovine serum albumin into a cellulose pad, with an acid-base indicator dye covalently bound to the surface of the cellulose. The sensor is placed within a flow-injection optosensing system to monitor the change in pH, and subjected to a through evaluation, using the flow-injection technique; sensor stability (both dye and enzyme stability), speed of sensor response, sensor sensitivity, sensor-to-sensor reproducibility, response to a typical interferent, and sensor lifetime data are obtained. Sensor poisoning upon exposure to low levels of mercury, and subsequent regeneration of the immobilized enzyme pad, is investigated for use as an on-line mercury sensor. The urea sensor is also evaluated for use as a continuous monitor for urea in kidney dialysate. Enzyme Michaelis-Menten constants are determined for the immobilized urease, under given assay conditions, using a stopped-flow flow-injection technique.

22] Microenzyme sensors

Most organic compounds are determined by spectrophotometry. Electrochemical determination of these compounds has definite advantages as a sample solution does not need to be optically clear. Many biosensors have been developed providing methods for rapid and continuous measurement of various compounds. Additionally, implantable microbiosensors are required in medical fields. This chapter presents an enzyme field effect transistor (FET) that consists of an immobilized enzyme and a FET. It also describes a urea-sensitive device based on a gas-sensing FET (enzyme transistor). The chapter describes two types of microsensors. The first one is a urea sensor consisting of immobilized urease and an ion-sensitive field effect transistor (ISFET). The other is a glucose sensor composed of immobilized glucose oxidase and an oxygen microsensor fabricated by using an anisotropic silicon etching technique. The fundamental characteristics of the oxygen sensor fabricated using the anisotropic etching techniques are also examined.

Biosensors Using Flowers as Catalytic Material

Abstract The ability of flowers and blossoms to convert biochemical substrates into volatile products is utilized for the development of biosensors using such plant tissues as catalytic components. It is shown that both minced and intact tissue portions from carnation and chrysanthemum flowers can be coupled with potentiometric ammonia gas sensing electrodes to prepare sensors for urea and some amino acids with good response properties. Surprisingly different response and selectivity patterns are found among species of flowers and for the structural subelements of a single type of flower.

Fabrication of potentiometric enzyme sensors based on a pH-sensitive polymer-coated Ag electrode.

A silver wire electrode coated with a poly (vinyl chloride) /tri-n-dodecylamine composite membrane was used to fabricate potentiometric enzyme sensors. The coated Ag electrode was further covered with a penicillinase or urease membrane to make a penicillin or urea sensor, respectively. The penicillin sensor was useful for determining penicillin at concentrations of millimolar level. Some operating variables such as pH and ionic concentration of the working buffer of the sensor were examined. The urea sensor could be used to determine urea in human blood.

Urea sensor based on an ion-sensitive field effect transistor. IV. Determination of urea in human blood.

A potentiometric method for the determination of urea in human blood with an ion-sensitive field effect transistor coated with a urease-albumin membrane is described. The urea sensor exhibits a potentiometric response to urea concentrations in the range of 0.1-10 mM with a response time of ca. 3 min. Urea concentrations of diluted serum and plasma can be determined accurately with the sensor. Comparison with an official method (i.e. the urease-indophenol method) gave satisfactory results.

The pH-static enzyme sensor : An ISFET-based enzyme sensor, insensitive to the buffer capacity of the sample

An ISFET-based urea sensor is combined with a noble-metal electrode which provides continuous coulometric titration of the products of the enzymatic reaction. The sensor thus becomes independent of the buffer capacity of the sample; and because the enzyme is operating at a constant pH, the linear response range is expanded.

Urea and Glucose Sensors Based on Ion Sensitive Field Effect Transistor with Photolithographically Patterned Enzyme Membrane

A polyvinylpyrrolidone (PVP) based photocrosslinkable polymer has been used to make an enzyme membrane on an ion sensitive field effect transistor (FET). An enzyme and a lysine-rich polypeptide were added to a PVP solution containing 2, 5-bis(4′-azido-2′-sulfobenzal)-cyclopentanone as a photocrosslinking reagent. Using an integrated FET having two ion sensitive elements, an enzyme membrane on the gate surface of one of the two ion sensitive elements was formed by the spin-coating of the enzyme-PVP solution, followed by UV-irradiation on the gate area of the FET and development in a 3% glutaraldehyde solution. The method was used to make enzyme membranes for a urea sensitive and a glucose sensitive FET. Both sensors were evaluated by using a 0.3ml flow-through cell. The 100% response times were 25s and 15s for urea and glucose determination, respectively. The relative standard deviations for determination of urea and glucose with the sensors were less than 2% over the concentration range studied. The application of the urea sensitive FET to ex vivo serum assay is also described.

Urea sensor based on an ion-sensitive field effect transistor. III Effects of enzyme load and ionic strength on the potentiometric response.

The effects of ionic strength of the sample solution and enzyme load on the potentiometric response of a urea sensor based on an ion-sensitive field effect transistor (ISFET) were examined. The output voltage of the sensor for urea solutions shifted slightly when NaCl was added to the solutions. The enzyme load on the ISFET gate affected the potentiometric response significantly. The sensor showed a higher response when the ISFET gate was coated with an enzyme membrane with a higher content of urease.

An Enzyme microsensor for urea based on an ammonia gas electrode

A urea microsensor was fabricated by immobilizing urease at the tip (10-μm diameter) of a rapidly responding ammonia gas microelectrode based on antimony. The construction and evaluation of both the urea senson and the ammonia electrode are described in detail. The urea sensor responds to 10 −2−10 −4 M urea in 30–45 s.

Urea sensor based on an ion sensitive field effect transistor. II. Effects of buffer concentration and pH on the potentiometric response.

Urea sensor based on an ion sensitive field effect transistor. II. Effects of buffer concentration and pH on the potentiometric response.

Solid-phase optoelectronic sensors for biochemical analysis

Simple solid-phase optoelectronic sensors for penicillin, urea, and glucose are described. Triphenylmethane dyes such as bromcresol green and bromthymol blue were derivatized with glutathione and co-immobilized with appropriate enzymes to a transparent membrane sandwiched between a red-light-emitting diode and a silicon photodiode with integral amplifier. In the presence of the corresponding substrates, catalytic action in the enzyme-dye membrane perturbs the local pH and causes characteristic color changes in the membrane which are monitored as a rise or fall in the output voltage of the detector system. With enzymes such as penicillinase, urease, and glucose oxidase, the response of the optoelectronic sensors is extremely reproducible over the concentration range 0–10 mM penicillin G, urea, or d-glucose, respectively. This report describes the construction and operation of these simple, inexpensive, and reagentless optoelectronic sensors.

Urea sensor based on ion sensitive field effect transistor coated with cross-linked urease-albumin membrane.

The gate of ion sensitive field effect transistor (ISFET) was coated with urease-albumin membrane to fabricate a micro urea sensor. Potentiometric response of the sensor is markedly dependent on the nature of the membranes. Using the sensor with a thiner membrane (ca. 2μm), linear response with a slope of -44 mV/decade has been obtained over the range of 1×10-4-5×10-3mole/dm3 (M) urea concentration, response time being 2 min. In contrast, for the thicker membrane (ca. 10 μm), Nernstian response with 30 min of the response time has been obtained. The diffusion rate of H+ or OH- in the membranes has been estimated to be a main factor governing the response time of the sensor. Some operating variables such as the buffer concentration and the life time of the sensor have been also examined.