Wladyslaw Torbicz

The pH-detection of triglycerides

Abstract This paper presents an indirect method of triglycerides determination based on pH-detection. The system consisted of a microreactor containing silica gel beads with surface immobilised lipase and the pH-sensor of ISFET type. Three methods of lipase immobilisation: (1) the chemical bond to the surface of glass beads coated with keratin, (2) entrapment within alginate gel beads and (3) adsorption onto nitrocellulose sheets were compared. All methods of lipase immobilisation, except the second one, were found to be effective. The systems consisting of microreactors packed with surface immobilised lipase were calibrated for different substrates. The highest sensitivity was obtained for tributyrin (0.478 pH/mM for concentration

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.

LTCC Enzymatic Microreactor

A novel three dimensional LTCC (Low Temperature Co-fired Ceramics) based microreactor with immobilized enzyme (urease) is presented in this paper. The microreactor consists of two chambers separated by a threshold. The shape of the chambers was optimized by the Finite Elements Method. The modeling has brought a better understanding of the microflow of chemically modified glass or polymeric beads through the microreactor. The modeling results are verified by the observation of the fluid movement inside the real structure via a top transparent polymer layer. Moreover, immobilization techniques of enzymes on polymeric beads are investigated. Finally, the properties of the LTCC microreactor are compared with the properties of a similar one made in silicon.

Immobilisation of bioreceptors for microreactors

In this paper, immobilisation techniques of bioreceptors for microsystems are presented. A method of silicon surface modification for biomolecules immobilisation under mild conditions was analysed. The method is based on the alkilation reaction between amino groups of the biomolecule and epoxy terminal on the surface. For chemical immobilisation of the bioreceptors, glycidoxypropylethoxysilane and 3-glycidoxypropylmethoxysilane were used. Evaluation of the immobilisation procedures was performed in a flow system.

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.

Temperature compensation electronics for ISFET readout applications

This paper presents temperature compensation electronics for ion sensitive field effect transistor (ISFET) sensors. It consists of a bridge-type floating-source ion sensing circuit and a VT extractor centigrade temperature sensor accompanied with a temperature coefficient (TCF) cancellation method. Using LabVlEW packages has developed an extended measurement system including compensation algorithms programming. Experimental results show that the temperature dependence of the Si/sub 3/N/sub 4/-gate ISFET sensor improved from 8mV//spl deg/C to near 0mV//spl deg/C with the proposed temperature compensation circuitry. This system allows a wide range of high accurate pH-level measurements. The method of temperature compensation may also be valid for other biosensors or bioFETs.

A new body-effect elimination technique for ISFET measurement

This paper presents a new circuit technique to reduce the body-effect for more accurate ISFET measurement. In a floating source readout configuration, the most popular n-channel ISFET in a p-type silicon substrate is easily influenced by back gate bias. Based on a proposed bridge-type floating source circuitry, a current mirror and a MOS drawing the same drain current as the ISFET, the scheme allows reduction of influence of body effect. The proposed technique is simple and has a universal use for different kind of ISFETs

CMOS Readout Circuit Developments for Ion Sensitive Field Effect Transistor Based Sensor Applications

Biomimetic devices have become more and more important in modern life where populations are aging; and the applications of electronic tongue system to water quality and environmental monitoring have become a significant field all over the world. Electronic tongue system uses sensor arrays and signal processing techniques such as identification, classification and recognition for quantitative multi-component analysis and for artificial assessment of taste and flavor of various liquids (Cjosek & Wroblewsk, 2007). Ion Sensitive Field Effect Transistor (ISFET), an electrochemical and potential type sensor, has served as excellent candidate for various electronic tongue applications. The ISFET, invented by Bergveld in 1970, is a solid-state device that combines a chemically sensitive membrane with a MOS type field-effect transistor (Bergveld, 1970). Due to its small size, rapid pH response and rugged solid-state construction, the ISFET exhibits a number of advantages over conventional pH-glass electrodes. ISFET has been extensively studied in past 36 years (Bergveld, 1991 and 2003; Garde et al., 1995). The current status and trends of main ISFET-based research, shown in Fig.1, are (1) single and sensor array applications, (2) ISFET micro-system fabrication in a standard CMOS technology, and (3) diversified ISFET-based biosensor development. For example, the ISFET research topics in Taiwan for the past ten years (Yin et al., 2001; Chin et al., 2001; Chung et al., 2004, and 2008) are focused on the study of new sensing material, on fabrication technology and device structure development, on diversified field applications, on the study and improvement for non-ideal characteristics, and on new readout circuit development. Based on our previous researches, the key problems in readout circuit development are due to the inherent characteristics of ISFET and to the body effect caused by common substrate of sensor array applications. The inherent characteristics of ISFET, like time drift and temperature dependency, cause

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.