In this work, new graphene-based screen-printed electrodes are proposed as a new, cheaper alternative to more common electrodes for determination of dopamine. Electrodes were designed, manufactured and tested to look for correlations between different graphene weight percentages used in electrodes and oxidation peaks and sensitivity in dopamine determination. All electrodes were tested using cyclic voltammetry. For a reference, graphite electrodes were tested. With sensitivity of 0.0161 μA/μM and detection limit of 5.549 μM those electrodes showed potential promise in use of graphene for electrode material. In electrodes manufacturing, Laroflex and PMMA based vehicles were mixed in with graphene platelets with diameters ranging over 2 μm and thickness between 8-15 nm. Initial tests with electrodes screen printed with graphene layers of 150 μM showed very low response. 0.0077 μA/μM sensitivity and 11.970 μM detection limit were achieved with Laroflex based electrodes. Further testing with thicker layers gave more impressive results with detection limit going as low as 1.349 μM and 0.1343 μA/μM sensitivity. Such results bring those electrodes to comparable level with other electrodes available.
This paper presents an electronic tongue system with blind source separation (BSS) and wireless sensor network (WSN)
for remote multi-ion sensing applications. Electrochemical sensors, such as ion-sensitive field-effect transistor (ISFET)
and extended-gate field-effect transistor (EGFET), only provide the combined concentrations of all ions in aqueous
solutions. Mixed hydrogen and sodium ions in chemical solutions are observed by means of H+ ISFET and H+ EGFET
sensor array. The BSS extracts the concentration of individual ions using independent component analysis (ICA). The
parameters of ISFET and EGFET sensors serve as a priori knowledge that helps solve the BSS problem. Using wireless
transceivers, the ISFET/EGFET modules are realized as wireless sensor nodes. The integration of WSN technology into
our electronic tongue system with BSS capability makes distant multi-ion measurement viable for environment and
water quality monitoring.
In this paper, we present the design of electronic tongue system for multi-ion sensing applications. The ion-sensitive
field-effect transistor (ISFET) detects the concentration of a particular ion in aqueous solution. However, when the given
chemical solution contains two or more ions, the ISFET sensor can only provide the combined concentration of ions. In
this end, our electronic tongue included a blind source separation (BSS) method of independent component analysis (ICA) to process the ISFET signals and to extract the concentrations of individual ions in the solution. The results of ISFET modeling based on fixed interference method (FIM) serve as a priori knowledge to help solve this blind source problem. Experiments are conducted on this electronic tongue system using aqueous solution containing hydrogen and sodium ions flowing through the array of dual H+ ISFET devices. The results of ICA processing successfully determined the concentration of hydrogen ions amidst the presence of sodium ions. This capability of ion separation allows us to move towards the development of smart electronic tongue systems for environmental and water quality monitoring.
This paper presents an analog processor design for ion sensitive field effect transistor (ISFET)-based flow through
system and its application in smart living space. The dynamic flow-cell measurement explores more information
compared to stationary measurement and is useful in environmental monitoring and electronic tongue systems. The
multi-channel floating source readout circuitry has been developed for flow-through analysis of ion sensitive field effect
transistor based array. The flow injection analysis system with two different ISFET structures has been investigated by
using performance parameters such as sensitivity, uniformity, response time of pH sensing. In addition, a self-tuning
multi-sensor water quality monitoring system based on adaptive-network-based fuzzy interference system (ANFIS)
learning method is developed. The results can be directly used in drinking water and swimming pool monitoring for
improving living space and quality.
In this paper preliminary results related to amperometric sensors fabricated in different technologies including thick- and thin-film technology are presented. The three-electrode sensors were designed as disposable ones and for monitoring. Disposable sensors were made by the screen-printing of the electrode material on polymeric foils, the other ones were made by screen-printing on ceramic or by platinum evaporation onto silicon wafer. Potential applications of the developed amperometric sensors for enzymatic, enzyme-cofactor mediated assays and phenothiazine-based drug detection were demonstrated. It was stated that, the PPy layer deposition on Pt electrode might lead to use of this material to decrease an oxidation potential of NADH in the NAD regeneration process.
In this paper a method of urease immobilization on the surface of the Siloprene membrane of the ammonium ion sensitive ChemFET is presented. The usability of the sensor for determination of urea in solutions at pH typical for biological fluids (pH 6 to pH 7.5) has been investigated. Due to the fact that the sensor exhibits high sensitivity to samples of low buffer capacity, the method of preliminary sample treatment, consisting in addition of buffers at adequate buffer capacity was developed. The sensors were tested in dialysate and blood plasma.
This paper presents results concerning the optimization of the measuring system of ImFET model based on the ISFET and ELISA test scheme. In the developed model of the ImFET we obtained linear changes of pH as a function of logarithm of antibodies concentration.
The reported back-side contact sensor were fabricated using a standard IC technology. The silver/silver chloride layers were deposited using electrochemical technique. The sensor chips were passivated with silicon nitride layer deposited by LPCVD, which ensure the stability of measurements. Preliminary examination of prepared sensor included the evaluation of their electrical properties and potentiometric response toward chloride. It was found that 19 sensors among 20 exhibited fast and reversible response toward chloride. Near theoretical slopes were obtained over the 10-4- 10-1 M chloride concentration range. The response time was shorter than 10S. The statistical evaluation, the calibration curves and the dynamic response of 20 sensors tested at the same time indicates that the proposed technology ensures preparation of sensor chips in a very reproducible way.
The construction of both the backside contacts and the package for replaceable sensor structure bonding has been described in the paper. Some aspects of technological process for backside contact performance are discussed in the report too. The measurement results from the structure test proved small and stable contact resistance when sensor structures have been changed in the package more than 100 times. A new method of changeable package has been shown.
This paper describes the development of NH4+- sensitive membranes based on various polymer materials incorporating nonactine as the ionophore for long-term performance CHEMFETs. Different composition of membranes based on plasticized PVC, carboxylated PVC, plasticized PVC modified by decylmethacrylate, polysiloxane and Siloprene were studied. Although polysiloxane membrane presented the most improved adhesion to the chip surface, the Siloprene membrane was successfully applied to design durable NH4+-sensitive CHEMFETs. These sensors showed NH4+-responses with good selectivity even after 14 months of continuous exposure to conditioning electrolyte.
In this work the application of a-Si:H thin film transistor technology in the field of chemical sensors is presented. In particularly, the optimization of magnetron deposition process for obtaining various silicon nitride films and TFT structures are described as well as adequate structures of Ion Sensitive Field Effect Transistor with respect to the ion sensitive hydrogen properties are studied. The device shows a good Nernst response and high reproducibility but not acceptable stability yet.
In this paper, a simple chemical method of urease immobilization on silicon nitride surface is described. As a basic structure to construct urea-biosensor, a pH-sensitive Si3N4-gate ISFET was used. The developed method of chemical immobilization of urease is based on Schiff's base formation. The developed EnFET type urea biosensor are characterized by the following parameters: (1) maximum analytical signal: 120 divided by 140 mV in 10 mM phosphate buffer solution, (2) linear range of the (Delta) Ugs equals f(logCurea): pCurea(2 divided by 3.5) in 10 mM phosphate buffer, (3) response time: 80 s and (4) lifetime: 35 days with the stable analytical signal then after 52 days this signal decreased by at least 40%. The influence of the concentration as well as the pH of the buffer solution on EnFET response were investigated.
Long-term stability of ion sensitive field effect transistors with inorganic membranes, dependent on the time drift phenomena is analyzed. The results presented in the paper relate to the Si3N4, Al2O3 and Ta2O5 membranes pH-ISFETs drift with the respect to the following parameters: sensitivity, linearity, linear time drift coefficient of threshold voltage and hysteresis.
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