Marek Dawgul

OPTIMISATION METHODS OF ENZYME INTEGRATION WITH TRANSDUCERS FOR ANALYSIS OF IRREVERSIBLE INHIBITORS

Abstract Manufacturing and application of biosensors cause some problems, the main of which are: (1) optimisation of enzyme immobilisation process to preserve bio-molecular enzyme structures and maximal value of enzyme activity and (2) development of approaches to accomplish a repeated analysis of substances which are irreversible inhibitors of the above mentioned molecules. In this paper both problems are analysed. For stabilisation of the structure of β-glucose oxidase, urease and cholinesterases during their immobilisation, the following approaches were examined: (1) application of one or a combination of the following chemical substances: protein, saccharose, glycerol, and specific substrates or their analogues; (2) optimisation of crosslinking methods including application of bi-functional reagents in aqueous and vaporous phases and (3) proper adjustment of technological operation times. Optimisation of these processes allows to preserve about 70–80% of initial enzyme activity. For the repeated analysis of organophosphorus pesticides and heavy metal ions, which are irreversible inhibitors of enzymes, the following approaches were applied: (1) treatment of enzyme membrane by special reactivating reagents and (2) application of easily replaceable enzymatic membrane. Methods of preservation of enzymatic sensors with use of sodium azide, EDTA and DTT were tested. Optimal conditions of sensor’s preservation and reactivation were chosen.

Na+-selective ChemFETs based on a novel ionophore: bis(phenylbenzo)-13-azocrown-5

Abstract This paper presents performances of ChemFETs based on a novel sodium ionophore bis(phenylbenzo)-13-azocrown-5. The main feature of the ionophore is its increased lipophilicity. This study shows that ChemFETs based on the novel ionophore exhibit a relatively high selectivity coefficient for sodium over lithium ions K (Na + /Li + ) pot , and that it is elevated for ChemFETs with PVC membrane containing o -nitrophenyl octyl ether ( o NPOE) as a plasticizer. Moreover, a significant difference in selectivity coefficients for Na + over Ca 2+ ions, also depending on a plasticizer, was observed. In addition, procedure of synthesis of the ionophore is also described. A good stability of the output signal was obtained for Na + -ChemFETs based on Siloprene membrane.

Optimization of a PVC Membrane for Reference Field Effect Transistors.

For the miniaturization of ISFET sensing systems, the concept of a REFET with low ion sensitivity is proposed to replace the conventional reference electrodes through the arrangement of a quasi reference electrode and a differential readout circuit. In this study, an ion-unblocking membrane was used as the top layer of a REFET. To optimize the REFET performance, the influences of the silylating process, different plasticizers, and the composition of the PVC cocktails were investigated. A low sensitivity (10.4 ± 2.2 mV/pH) and high linearity (99.7 ± 0.3 %) in the range from pH 2.2 to pH 11.6 was obtained for the REFET with a 60 wt.% DNP/(DNP + PVC) membrane. To evaluate the long term stability, the drift coefficient was estimated, and for the best REFET, it was −0.74 mV/h. Two criteria for assessing the lifetime of REFETs were used, namely the increase in pH sensitivity to a value higher than 15 mV/pH and the degradation of linearity below 99 %. For the best REFET, it was approximately 15 days.

An Electronic Tongue System Design Using Ion Sensitive Field Effect Transistors and Their Interfacing Circuit Techniques

This paper proposes an electronic tongue system design using ion sensitive field effect transistors (ISFETs), extended-gate FET (EGFET) and their interfacing circuit techniques. Bridge-type constant voltage, constant current, and temperature compensation circuitries have all been developed for ISFET to sense hydrogen and chloride ions for water quality monitoring applications. This design offers a sensitivity of over 54 mV/pH and an improved temperature coefficient (T.C.) of 0.02 mV/degC; in addition, a sensitivity of 43 mV/pCl can be achieved by using a proposed extended-gate FET with a mixed polyvinyl chloride (PVC), chloride ionophore III (ETH9033) and lipophylic salt on the indium-tin-oxide (ITO)/glass substrate.

EnFET for urea determination in biological fluids using ammonium ion detection

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.

ISFET electronic tongue system for environmental multi-ion sensing with independent component analysis signal processing

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.

Urea biosensors and their application in hemodialysis--perspective of EnFET application.

Parameters such as blood urea nitrogen concentration, normalized protein catabolic rate and Kt/V that are utilized for urea concentration measurements in blood and dialysate for the optimization of the hemodialysis process are reviewed in the paper. Basic methods of urea concentration measurement are described. Urea biosensors of the EnFET type based on the pH-sensitive Si3N4 gate FET and pNH4-sensitive FET with a Siloprene membrane containing nonactine, both of our own construction, are presented. Application of these biosensors for urea concentration measurement in blood and dialysate is described. An experimental microdialysis system with urease in detector solution and a pH-ISFET detector are described. A comparison of two dialysis procedures, with a commercial dialysate an initial of pH 5.6 and with pH kept lowered during the dialysis process applied to rats, is given.

Spiral Concentric Two Electrode Sensor Fabricated by Direct Writing for Skin Impedance Measurements

In this paper, six versions of novel impedance sensors with electrodes of a form of two parallel spirals with different distances between conducting paths were elaborated. The electrodes were fabricated by direct writing technique with the use of gold polymer paste. To avoid an influence of anisotropic properties of the skin on measurements of the skin impedance, the spiral two-electrode sensors were proposed. Four resistance–capacitance-Warburg impedance models of the electrode/skin interfaces were proposed and tested. MilliQ water, KCl water solution at a concentration of 0.01 M, and human skin were used for the verification of adequacy of these models to fit the experimental data. It was stated that two of these models, A and B, have best fit to the experimental data. For measurements of skin with expected high impedance (dry skin), the sensors with the smaller distance between electrodes (version 2) should be used. Otherwise, when a patient has wet skin, which correlates with low impedance, the sensors with the larger distance between electrodes (version 7) should be applied. This is especially required when the measurements are carried out using mobile equipment, which typically has limitations related to the minimal measured impedance value.

Transcutaneous Blood Capnometry Sensor Head Based on a Back-Side Contacted ISFET

Authors present the construction of an electrochemical sensor head for non-invasive measurements of CO2 tension in arterial blood. The main element of the capnometric sensor under development is a Back Side Contacted Ion Selective Field Effect Transistor. The transcutaneous sensor head consists of a plastic housing, in which the ISFET chip, an Ag/Cl reference electrode, a thermistor, a heating element, and a membrane that is permeable by gases are mounted. The design and fabrication technology of the BSC ISFET, as well as some preliminary experimental results obtained using the designed capnometric sensor head, are presented in this paper.

Development of NH4+-sensitive polymer membranes for long-term performance microsensors

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.