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p. 119-127
Received: 7 April 2003 / Accepted: 14 May 2003 / Published: 28 June 2003
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| Cited by 7 | PDF Full-text (341 KB)
Abstract: The realisation of a miniaturised potentiometric enzyme biosensor is presented. The biosensor chip utilises the enzyme organophosphorus hydrolase (OPH) for the direct determination of pesticides. The transducer structure of the sensors chip consists of a pH-sensitive capacitive electrolyte-insulator-semiconductor (EIS) structure that reacts towards pH changes caused by the OPH-catalised hydrolysis of the organophosphate compounds. The biosensor is operated versus a conventional Ag/AgCl reference electrode. Measurements were performed in the capacitance/voltage (C/V) and the constant capacitance (ConCap) mode for the two different pesticides paraoxon and parathion. For the development of this new type of biosensor, different immobilisation strategies, influence of buffer composition and concentration, transducer material, detection limit, long-term stability and selectivity have been studied.
p. 128-145
Received: 15 April 2003 / Accepted: 21 May 2003 / Published: 28 June 2003
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| Cited by 9 | PDF Full-text (409 KB)
Abstract: The electrochemical studies on the behaviors and recognition of DNA have attracted cosiderable attention. DNA biosensors based on a nucleic acid hybridization process are rapidly being developed towards the goal of rapid and inexpensive diagnosis of genetic andinfectious deseases. This brief review focuses on the current state of the DNA electrochemical sensors with emphasis on recent advances, challanges and trends. The works on DNA electrochemical behaviors, recognition and detection in our group in the last three years are also introduced.
p. 146-159
Received: 16 April 2003 / Accepted: 3 June 2003 / Published: 28 June 2003
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| Cited by 4 | PDF Full-text (382 KB)
Abstract: A complex deposition procedure of the hydrogel layer of modified poly(2-hydroxyethyl methacrylate) (polyHEMA) covalently linked to the silicon nitride surface and covering only the gate area of the ISFET, was optimized for photolithographic technology, using standard silicon wafers of 3” diameter. The influence of hydrogel composition and layer thickness on the sensors’ parameters was investigated. It was shown, that ISFETs covered with more than 100 μm thick polyHEMA layers in restricted pH-range could be practically insensitive to pH. Regarding mechanical stability of ion-selective sensors, a polyHEMA layer of ca. 20 μm thickness was found to be the best suitable for further manufacturing of durable ion selective sensors (Chemically modified Field-Effect Transistors – ChemFETs). The weak buffering properties of the thin polyHEMA layers had no disadvantageous influence on the sensors’ function.
p. 160-165
Received: 16 April 2003 / Accepted: 16 June 2003 / Published: 29 June 2003
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| Cited by 7 | PDF Full-text (191 KB)
Abstract: In this paper urea biosensors based on detection of pH and ammonium ions are presented. As transducers pH-sensitive ion-selective field effect transistors (ISFETs) and chemically modified FETs (ChemFETs) snsitive to ammonium ions were used.Results concerning urea determination by the bisensors in blood plasma and in dialysate show that the biosensors can be applied for urea monitoring in the effluent dialysate. However in the case of pNH4 based EnFETs a special pre-treatment (dilution with tris/HCl buffer) of the samples is necessary.
p. 166-175
Received: 1 April 2003 / Accepted: 5 May 2003 / Published: 29 June 2003
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| Cited by 36 | PDF Full-text (189 KB)
Abstract: The relevance of polyphenols in human health is a well known fact. Prompted by that, a very intensive research has been directed to get a method to detect them, wich will improve the current ones. Laccase (p-diphenol:dioxygen oxidoreductase EC 1.10.3.2) is a multi-copper oxidase, wich couples catalytic oxidation of phenolic substrates with four electron reduction of dioxygen to water [1]. A maximum catalytic response in oxigenated electrolyte was observed between 4.5 and 5.5 [2], while for pH > 6.9 the laccase was found to be inactive [3]. We prepared a biosensor with laccase immobilised on a polyether sulphone membrane, at pH 4.5, wich was applied at Universal Sensors base electrode. Reduction of the product of oxidation of several polyphenols, catalysed by laccase, was done at a potential for wich the polyphenol of interest was found to respond. Reduction of catechol was found to occur at a potential of -200mV, wich is often referred to in the literature for polyphenolic biosensors. However other polyphenols did not respond at that potential. It was observed that (+)- catechin produced a very large cathodic current when +100mV were applied to the laccase biosensor, both in aqueous acetate and 12% ethanol acetate buffer, whereas caffeic acid responded at -50mV. Other polyphenols tested were gallic acid, malvidin, quercetin, rutin, trans -resveratrol
p. 176-186
Received: 1 April 2003 / Accepted: 29 April 2003 / Published: 30 June 2003
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| Cited by 19 | PDF Full-text (756 KB)
Abstract: Thick films Nickel oxide (NiO) in the form of pn-junctions and planar structures with interdigitated electrodes were investigated for γ -radiation dosimetry purposes. Samples were fabricated using the thick film screen-printing technique. All devices were exposed to a disc-type 137 Cs source with an activity of 370 kBq. They showed an increase in the values of current with the increase in radiation dose up to a certain level. Performance parameters of the devices, such as sensitivity to γ -radiation exposure and working dose region, were found to be highly dependant on the composition of the materials used.
p. 187-191
Received: 31 March 2003 / Accepted: 3 May 2003 / Published: 30 June 2003
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| Cited by 5 | PDF Full-text (189 KB)
Abstract: The Impedance analysis technique complimented with curve fitting software was used to monitor changes in film properties of Thickness Shear Mode (TSM) resonator on vapour exposure. The approach demonstrates how sensor selectivity can be achieved through unique changes in film viscosity caused by organic vapour adsorption.
p. 192-201
Received: 27 March 2003 / Accepted: 8 May 2003 / Published: 30 June 2003
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| Cited by 7 | PDF Full-text (618 KB)
Abstract: Hydrogen ion selective membranes formulated with 3140 RTV silicone rubber (SR) in PVC were studied to extend the life time of solid state ion sensors through improved membrane adhesion. All solid state hydrogen ion selective electrodes were prepared by incorporation of tridodecyl amine (TDDA) as an ionophore, potassium tetrakis[3.5-bis(p-chlorophenyl)borate (KTpClPB) as a lipophilic additive, bis(2-ethylhexyl)adipate (DOA) as a plasticizer. Their linear dynamic range was pH 2.0-11.0 and showed the near Nernstian slope of 55.1±0.2 mV/pH (r=0.999). The ifluences from alkali and alkaline earth metal ions were studied for the response of the final ISE membrane composition. Impedance spectroscopic data showed that the resistance was increased by increasing SR content in PVC. Brewster Angle Microscopy (BAM) image showed clear differences according to the SR compositions in PVC. Life time of the all solid state membrane electrode was extended to about 2 months by preparing the membrane with PVC and SR. The standard reference material from NIST (2181 HEPES Free acid and 2182 NaHEPESate) was tested for the ISE and it gave good result.
Displaying article 1-8
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