22/11/2017 8:50 PM

BVT Products were used in below mentioned publications

 

Screen Printed Electrodes with Impoved Mass Transfer

KREJCI J., SEJNOHOVA R. , HANAK V. , VRANOVA H.
http://www.intechopen.com/articles/show/title/screen-printed-electrodes-improve-mass-transf

 

 

Microflow Vessel Improving Reproducibility and Sensitivity of Electrochemical Measurements
KREJCI J., LACINA K., VRANOVA H., GROSMANOVA Z.
A new microflow system was designed and developed for electrochemical measurements. The electrochemical electrodes prepared using thick film technology were used in this arrangement. Results of the various measurements such as simple amperometric measurement on the example of H2O2 detection, measurement with Glucose Oxidase (GOx) biosensor, soluble enzyme activity measurement etc. carried out using this system have been shown. It was observed that the sensitivity and reproducibility of the electrochemical measurements is improved significantly. The new device performance was proved on H2O2 detection, activity of GOx measurement and heavy metals detection (measured concentration range: H2O2 10-9 to 10-1 M, glucose 10-6 to 10-2 M, activity of GOx 10-1 to 102 IU, heavy metals (Cu, Pb) 10-4 to 10-3 M ). The microflow insert greatly reduces the overall size of the electrolyte vessel and measurements with sample quality as low as 2 ml can be accomplished.
Bibliographic citation: Krejci J, Electroanalysis, 2008, 20, 2579-2586

 

 

The determination of tetracycline residues in food using a disposable screen-printed gold electrode (SPGE)
MASAWAT P., SLATER J. M.
The electrochemical analysis of tetracyclines was investigated using a gold screen-printed electrode by cyclic voltammetry and flow injection analysis with dc amperometry. Cyclic voltammetry was used to study the electrochemical oxidation of tetracyclines. For all the tetracyclines investigated a well-defined cyclic voltammogram providing the highest peak current, at 1.2 V versus Ag/AgCl, was obtained when using potassium dihydrogen phosphate solution at pH 2. Flow injection analysis with dc amperometry using the specially fabricated wall-jet flow-through cell was also studied. Under amperometric conditions (Eapp= 1.2 V; flow rate =2.0 mL min-1), analytical calibration graphs for tetracycline, chlortetracycline and oxytetracycline were obtained from 1 to 500, 5 to 50 and 1 to 500 μmol L-1 with detection limits of 0.96, 0.58 and 0.35 μmol L-1, respectively. The proposed method was successfully applied to the determination of tetracycline, chlortetracycline and oxytetracycline in pharmaceutical products and foods.
Bibliographic citation: Masawat P, Sensors and Actuators B, 2007, 124, 127-132

 

Soft landed protein voltammetry
Pepi F., Ricci,A.,  TataA., Favero G., FrasconM., Delle Noci S., Mazze F.
The present work illustrates a new method: soft landed protein voltammetry (SLPV); this experimental procedure is based on the coupling of ion soft landing with a voltammetric technique and allows the electrode surface to be functionalized with biologically active molecules, thus opening up numerous new perspectives ranging from molecular electronics to protein chips.
Bibliographic citation: Pepi F, Chem. Commun., 2007, 3494-3496

 

 

Determination of bacterial antigens using a multichannel immunoenzyme amperometric sensor
SAFINA G. R.; MEDYANTSEVA E. P.; BAZARNOVA O. N.; GLUSHKO N. I.; BUDNIKOV G. K.
A procedure for the individual determination of the antigens of the conditionally pathogenic microorganisms Streptococcus pyogenes and Staphylococcus aureus present in combination using a multichannel immunoenzyme amperometric sensor based on a screen-printed electrode was developed. Conditions for fabricating the biosensing part and for the operation of the sensor (the matrix component, the ratio between biocomponents, and the substrate concentration) were chosen. The determination limits of bacterial antigens obtained using the analytical device were equal to 5 x 10-9 mg/mL. It was found that bacterial antigens simultaneously present in serums from patients can be determined using the sensor developed.
Bibliographic citation: Safina G R, Journal of Analytical Chemistry, 2006, vol. 61, No. 9, pp. 912-916

 

 

A steady-state and flow-through cell for screen-printed eight-electrode arrays.
DOCK E., CHRISTENSON A., SAPELNIKOVA S., KREJČÍ J., EMNÉUS J., RUZGAS T
An electrochemical cell has been developed enabling amperometric steady-state- and flow-injection measurements with screen-printed arrays consisting of eight working electrodes (Φ = 1 mm) arranged radially around a printed AglAgCl reference electrode in the centre. The cell contained a rotator, providing similar hydrodynamics over all the working electrodes in the array, which was manually centred under the rotator. The reproducibility of steady-state measurements with eight-electrode platinum or gold arrays in this cell was studied by measuring and comparing currents from ferricyanide reduction at each electrode in the array. It was found that the relative standard deviation (R.S.D.) for the currents at different electrodes on one array was below 5%. Similar R.S.D. was found if measurements were compared between several arrays. This indicates that manual insertior/positioning of the eight-electrode array in the cell and hydrodynamics at the electrodes provided measurement reproducibility similar to the reproducibility of manufacturing eight-electrode platinum or gold arrays by screen-printing. A comparative study was performed between screen-printed and through mask sprayed carbon arrays. It was found that the reproducibility of the sprayed arrays was similar to that of the platinum or gold screen-printed arrays, with R.S.D. values below 6% regarding the variation between electrodes within the same array and the variation between different arrays. To enable flow-injection measurements, a tube (0.4 mm inner diameter) was inserted into a hole drilled through the centre of the steady-state cell rotator. This construction made it possible to inject the solution into the cell through the tube (not rotating), while the rotator was spinning over the eight-electrode array, It was found that this combination of flow-injection and mixing by a rotator provided a uniform current response over the array electrodes and that, at optimum conditions, the R.S.D. values between the eight electrodes in the array were nearly the same as in case of the steady-state measurements, i.e., below 5%.
Bibliographic citation: In Analytica Chimica Acta 531, 2005. s. 165-172

 

 

Monolayers of photosystem II on gold electrodes with enhanced sensor response - effect of porosity and protein layer arrangement.
MALY, J., KREJČÍ, J., ILIE, M., JAKUBKA, L., MASOJÍDEK, J., PILLOTON, R., SAMEH, K., ŠTEFFAN, P., STRYHAL, Z., SUGIURA, M.
Mass transport of the bulk of the analyte to the electrode and through the bioactive layer can be significantly improved by use of the nanoelectrode array and defined arrangement of protein film. This phenomenon has been studied by (i) atomic-force microscopy, (ii) electrochemical measurements of PSII activity, and (iii) digital simulations for an oriented monolayer of histidine-tagged photosystem II (PSII) immobilized on nitrilotriacetic acid (NTA)-modified gold electrodes. The output signal of the electrochemical biosensor is controlled by (i) mass transport from the bioactive layer to electrode and (ii) mass transport between the bulk of the analyte and the electrode. Mass transport through the bioactive layer was electrochemically studied for PSII self-assembled on gold screen-printed electrodes. A densely packed monolayer of PSII has a significant shielding effect toward the diffusion of redox mediator duroquinone (DQ). Mass transport to the planar electrode surface was improved by co-immobilization of bovine-serum albumin (BSA) as spacer biomolecule in the monolayer of PSII. Correlation between the electrochemical properties and surface arrangement of the resulting protein films was clearly observable and confirmed the improved mass-transport properties of structured enzyme monolayers. On the basis of this observation, the application of a bottom-up approach for improvement of electrode performance was proposed and digitally simulated for an infinite array of electrodes ranging in diameter from 50 nm to 5 μm. The nanoelectrode array, with the optimum time window selected for measurements, enables enhancement of mass transport between the bulk of the analyte and the macroelectrode by a factor of up to 50 in comparison with ‘‘classical’’ planar electrodes. Use of a time window enables minimization of crosstalk between individual electrodes in the array. The measurements require methods which suppress the double-layer capacity.
Bibliographic citation: Analytical and Bioanalytical Chemistry, 2005, roč. 381, č. 8, s. 1558-1567. ISSN: 1618- 2642.

 

Comparison of biosensoric and chromatographic methods for the detection of pesticides
GROSMANOVÁ, Z., KREJČÍ, J. , TZNEK, J., CUHRA, P., BARSOVA, S.
Screen-printed biosensors with immobilized acetylcholine esterase (AChE) were used for measuring fruit and vegetable samples that had first been analysed using gas and highperformance liquid chromatography. The output signal for the biosensors is the current, which is used to calculate relative inhibition (RI), a measured quantity. RI is proportional to the inhibiting (toxic) effect of organophosphates and carbamates. Measurements with AChE biosensors are not easily reproducible. This problem is solved by the choice of an arbitrary toxicity standard of 1.25 uM Syntostigmin. Measurements were evaluated by the ratio of the relative inhibition of the sample against the relative inhibition of Syntostigmin. Results obtained from the biosensor match those of chromatography in 19 out of 38 total measurements made and for nine out of 19 positive samples. The confirmation rate was 50%. Future work must check the limit of 0.1 and the independent control of inhibiting pesticides contents after measurements using the biosensor.
Bibliographic citation: 2005, roč. 85, č. 12- 13, s. 885 (s.)

 

 

Nanostructured Electrodes with the Enhanced Output Signal for Biosensor Applications
KREJČÍ, J., JAKUBKA, L., KHATIB, S., ŠTEFFAN, P.
The main goal of this project is to design a novel type of microparticle-structured electrodes and amperometric device capable of measurements within the range of femtoampers. This paper covers an area of electrochemical sensors, which monitored the behaviour of oriented monolayer of histidine tagged photosystem II from termophilic cyanobacteria Synechococcus elongatus deposited on surface of gold screen-printed electrodes. This electrode based on the four independent types of experiments monitoring.
Bibliographic citation: In 2nd International Workshop on Multianalyse Biosensing Devices. Tarragona, Spain: 2nd International Workshop on Multianalyse Biosensing Devices, 2004. s. 42 (s.)

 

The Biosensor Signal Analysis in Portable Microfluidic Device
FUJCIK, L., VRBA, R., KREJČÍ, J.
The biosensor signal analysis in portable microfluidic device [1] for organophosphorous pesticide toxicity analysis for field measurement is presented. Portable microfluidic device consists of two loop pumps. The first loop assures the mixing of solution. The 95 % of solution circulates through the first loop. The second loop consists of the capillary, which creates the hydrodynamic resistance, and of the chamber with biosensor. The 5 % of solution circulates through the second loop. The Artificial Synapsis (AS) [2] is integrated in the chamber with the biosensor. The AS detects the integral organophosphorous pesticide toxicity. Both parts are integrated in a compact device with size of 200 x 100 x 100 mm.
Bibliographic citation: In Proceedings of the WSEAS Conferences, Rio de Janeiro, Brasil 2004. Rio de Janeiro: WSEAS, 2004. s. 208 (s.) ISBN: 960-8457-03- 3.

 

A New Possibility of Thick Film Biosensors Substrate Properties Measurement
PRÁŠEK, J., KREJČÍ, J.
The aim of our work is to find effective way for study of TFT biosensors electrode substrates properties during biosensors fabrication, which is crucial question for the next development of this perspective technology. A new electrochemical analytical device was developed to ensure a defined mass transport to the electrodes, which is the most limiting process that influences the response quality of the sensor. The device consists of rotating conic vessel for measured sample and the thick film amperometric sensor trenching in. This new electrochemical analytical solution was registered for patenting. The biosensors’ substrate responses were tested on basic electrochemical couple of potassium ferrocyanide-ferricyanide. Thick film biosensor’s substrate response dependence on the liquid velocity and geometrical arrangement is presented.

 

Screen-printed sensors with graphite electrodes - comparison of properties and physical method of sensitivity enhancement.
KREJČÍ, J.; PRÁŠEK, J.; FUJCIK, L.; KHATIB, S.; HEJÁTKOVÁ, E.; JAKUBKA, L.
Screen-printed electrodes are widely used in construction of sensors. The use of graphite material is preferred due to its simple technological processing and low cost. Different graphite pastes are compared for hydrogen peroxide detection. The slope of the calibration curve, linearity and limit of detection have been compared for different pastes and technologies of graphite electrode preparation. The influence of the structure of the paste on response is discussed. Physical methods of sensitivity enhancement are proposed. All results are compared with platinum electrode as technological reference.
 

 

Equipment for chemical analysis
KREJČÍ, J., KUPKA, J., RUZGAS
 
 

 

 

Disposable electrochemical sensor for rapid determination of heavy metals in herbal drugs.
Palchetti I, Mascini M, Minunni M, Bilia A R, Vincieri F F
Analysis of herbal drugs and extracts need rapid and affordable methods to assure the quality of products. The application of the electrochemical sensors in the field of quality control of herbal drugs, herbal drug preparations and herbal medicinal products appears very promising, advantageous and alternative to conventional methods due to their inherent specificity, simplicity and for the fast response obtained. This paper presents a proposal about the application of disposable electrochemical sensors associated with electroanalytical instrumentation for the detection of heavy metal analysis in herbal drugs. In particular samples of St. John's wort were analysed applying anodic stripping voltammetry. The content of Cd and Pb were evaluated. The ICP spectroscopy was used as reference method.
Bibliographic citation: Palchetti I, J Pharm Biomed Anal. 2003 Jun 1;32(2):251-6.Click here to read

 

Calibration and Testing in Voltammetric and Amperometric Sensor Measurements.
ŠTEFFAN, P., ADÁMEK, M., VRBA, R., KREJČÍ, J., PRÁŠEK, J.
The novel testing and calibrating sensor for calibration and testing purposes in voltammetric and amperometric measurements is presented. The device consists of the only electronic components, and was designed to fit standard I-V characteristics of the electrochemical sensors as best as possible. The testing sensor was carefully simulated by PSPICE and tested in temperature chamber for temperatures from 10 to 40 °C. Wider temperature ranges may be added. This special sensor accelerates testing and calibration of all instruments used for voltammetric and amperometric methods.
Bibliographic citation: In 25th annual international conference of the IEEE engeneering in medicine and biology society. Cancun, Mexico: cancun, 2003. s. 3068 (s.) ISBN: 0-7803-7790- 7.

 

Characterization of Acetylcholinesterase by Electrochemical Sensor.
ONDRUCH, V., KREJČÍ, J., VRBA, R.
The electrochemical sensors enable to simplify the complicated biochemical methods to procedures which can be routinely used. Acetylcholinesterase is an enzyme which is connected with neuron function in brain and with information propagation in living bodies. The low activity of enzyme or damaged enzyme is connected with senile dementia and Alzheimer disease.
The simple measurement of apparent enzyme activity and apparent Michaelis-Menten constant has been developed. The method has been tested in vitro in different solutions. The method needs numerical calculations and it is generally nonlinear and numerically unstable. The conditions of numerical stability have been defined. The conditions of numerical stability have been involved into the experimental procedure and they are automatically tested during measurement procedure.
The method can selectively measure the properties of Acetylcholinesterase and Butyrylcholinesterase. The relation of both enzymes activities can be measured.
The method has been tested on full blood and plasma. The measurement needs 10 to 25 ul of blood (one drop of blood) and full time of analysis takes 15 minutes. It enables potential use of this method by practical physicians and it creates the tool for deep study of relation between Acetylcholinesterase properties and neurodegenerative diseases.
Bibliographic citation: In A new Beginning for Human Health. Cancún, Mexico: IEEE, 2003. s. 3071 (s.) ISBN: 0-7803-7790- 7.

 

The dependence of  TFT chemical sensors on the technology and the other influences
ADÁMEK M., KREJČÍ J. , SZENDIUCH I. 
The miniature electrochemical sensors can be produced by thick film technology. The optimal technology of TFT sensor production and optimal technological properties of thick film materials are main problems of design of sensors. The optimisation of TFT chemical sensor properties is discussed. The measurement of temperature characterisation can be used for these optimisations. The study of processes on the electrodes brings about the possibility of correlating the parameters of printed materials and technological processes of the production with the final sensor properties. This is the first step to the preparation of sensors with defined properties.
 

 

Modelování vlastností vodivostního čidla v závislosti na zmenšování jeho charakteristických rozměrů
HUBÁLEK J., KOLAŘÍK V., KREJČÍ J.
Další aplikací nových směrů ve vývoji senzorů jsou konduktometrická čidla. V makroskopickém měřítku jsou velmi dobře teoreticky popsána a již dlouhou dobu komerčně dostupná. Jejich miniaturizací však vzniká celá řada nových teoretických i technologických problémů. Jedním z nich je i geometrický tvar elektrod. Základní poznatky byly získány modelováním konduktometrického čidla pro chemické senzory kapalných roztoků. Elektrody s velmi malou charakteristickou vzdáleností řádově desítky μm se dnes začinají ve velké míře používat, zatím však převážně experimentálně. Takové elektrody nazýváme mikroelektrody nebo lDES (interdigitated electrods) a jsou většinou realizovány hřebínkovou strukturou použitím tenkovrstvé nebo tlustovrstvé technologie. Dosud nebyl dostatečně popsán vliv těchto elektrod na změnu impedance.
 

 

Testing of graphite paste properties for thick film sensors
ADÁMEK, M., PRÁŠEK, J., KREJČÍ, J
The miniature electrochemical sensors can be produced by thick film technology. The optimal properties of thick film electrode materials are main problems of sensors design. The optimisation of graphite paste for TFT chemical sensor properties is discussed. The commercial TFT graphite pastes, which are used for common application, are cheap and easily producible, but they are not efficient for electrochemical measurement. These pastes have insufficient sensitivity and they have other improper properties. Graphite pastes, which were designed for special chemical analysis, are technically known, but these pastes are not workable by screen-printing. The aim of this work is first step in rheologic properties addition to graphite electrochemical pastes. This will ensure the pastes printability that will enable the reproducible mass production.
The graphite powder mixed with paraffin is the basic component of common chemical graphite pastes. There were examined different properties of these pastes in dependence of graphite powder and binding material content in this work. The measurement was made in standard electrochemical couple of potassium ferrocyanide-ferricyanide.
Bibliographic citation: In 26th International Spring Seminaron Electronics TechnologyISSE 2003 Conference Proceedings. Technical University of KošicePark Komenského 2043 89 KošiceSlovak Republic: ETC GRAFO & BRIX, Poštová 13, 040 01 Košice, Slovak Republic, 2003. s. 344 (s.) ISBN: 0-7803-8002- 9.

 

Analysis of Enzyme Kinetics.
ONDRUCH, V., KREJČÍ, J.
This paper deals with basic theoretical principles of enzyme kinetics analysis, their implementation into the OFBio, control application for a Microflow system produced by Krejci Engineering Company. Theoretical principles are experimentally verified.
Bibliographic citation: In Electronic Devices and Systems 2003 - Proceedings. Brno: Brno University of Technology, 2003. s. 340 (s.) ISBN: 80-214-2452- 4.

 

Referentní elektrody připravené TFT technologií
METELKA R., TESAŘOVÁ E., KREJČÍ J., VYTŘAS K.
Stabilita potenciálu několika typů pseudoreferentních elektrod, připravených technologií tlustých vstev (TFT), byla potenciometricky sledována v elektrolytech různého chemického složení a pH. Byly testovány tyto konstrukční varianty TFT pseudoreferentních elektrod; typ l - vrstva směsi Ag a AgCl, typ 2 – vrstva Ag s elektrolyticky vyloučeným AgCl a typ 3 - pouze samotná vrstva Ag, vše vytištěno sítotiskem přes šablonu na podklad z aluminy. Kromě stability potenciálu byla také sledována a dokumentována odolnost materiálů elektrod vůči chemickému působení různých roztoků.
 

 

MS EXCEL AND STANDARDIZATION OF MEASUREMENT RESULT EVALUATION OF BIOSENSOR INPUT CONTROL
SAJDL, O., VRBA, R., KREJČÍ, J., FUJCIK, L.
Nearly in every practical part of some scientific project solution we meet demand to discover or verify a function of a developed device (instrument, sensor, etc.) This process (a measurement) is usually executed repeatedly and usually by various people. A practice shows that if we don’t unify the evaluation result, especially if we have  reater number of measurements (hundreds or more), it can cause its ambiguity and thereby to its depreciation. To prevent this depreciation, it is necessary jointly to interpret and to evaluate attained results – to standardize. Analysis and practical solution exploiting Microsoft Excel is presented in this paper.
Bibliographic citation: In Book of Summaries, XVII IMEKO WORLD CONGRESS, Metrology in the 3rd Millenium. Dubrovník: 2003. s. 245 (s.) ISBN: 953-7124-00- 2.

 

ARTIFICIAL SYNAPSIS – THE DETECTOR OF PESTICIDE TOXICITY.
HÁZE, J., SKOČDOPOLE, M., FUJCIK, L., VRBA, R., GROSMANOVÁ, Z.
Fast detection of organophosphorous pesticide toxicity in field conditions has not been fully solved yet. The new tool for field measurement of organophosporous pesticides toxicity is described. The detection is based on the inhibition of acetylcholinesterase. The enzyme acetylcholinesterase is immobilized on a miniature electrochemical detector, which is made by Thick Film Technology (TFT). The dimensions of TFT electrochemical sensor are 7,35 x 25,4 mm. The detector is placed in a narrow gap in which the analyzed sample and acetylthiocholine flow. This arrangement simulates the removal of acetylcholin from synaptic gap. It creates the simple model of synapsis - the Artificial Synapsis (AS). The AS detects the integral sample toxicity. It enables organophosporous pesticides traces to be detected in washout from leaves as well as their direct measurement in rivers, ponds, waste waters and drinking water sources. The preconcentration of the sample is possible. The detection limit varies in wide range depending on the toxicity of pesticide. Structure and function of AS is described. Limit of detection (LOD) was found for pesticide Syntostigmin 10-10 mol.
Bibliographic citation: Metrology in the 3rd Millennium - Proceedings. Dubrovnik, Chorvatsko: 2003. s. 2156 (s.) ISBN: 953-7124-00- 2.

 

ANALYZÁTOR TOXICITY PESTICIDŮ
UJCIK, L., KREJČÍ, J., VRBA, R., HÁZE, J., SKOČDOPOLE, M.
Provedení analýzy přímo v místě možné kontaminace, -cena jedné analýzy. Všechny výše uvedené body nejsou uspokojivě vyřešeny. Cena jedné analýzy je vysoká, minimálně se jedná o 1 000 Kč. Analýzu je navíc nutno provádět v laboratoři. Proto je časový odstup mezi odběrem vzorku a samotnou analýzou příliš velký (1 až 5 dní). Množství odebraných vzorků a jejich provedených analýz je velmi malé a pravděpodobnost nalezení pozitivního vzorku nízká. V roce 1999 bylo provedeno v jihomoravském kraji cca 400 odběrů vzorků dle vyhlášky, přičemž pozitivních nálezů bylo méně než 10. Kontrola je tedy velmi neefektivní.
Bibliographic citation: RADEŠÍN 2003. 2003. s. 39 ( s.)ISBN: 80-214-2497- 6.

 

Reproducibility of measurement of organophosphorous pesticides toxicity.
FUJCIK, L., VRBA, R., KREJČÍ, J., PRÁŠEK, J., GROSMANOVÁ, Z.
Fast detection of pesticide toxicity in the field conditions is very important in many aspects (pesticide storage, price of one test etc.). The measurement uses principle of an artificial synapse (AS) and inhibition of an enzyme Acetylcholinesterase (AChE). The AS is a very effective detector of the pesticide detector. This information is very different from classical analytic method data. The enzyme is sensitive to many external influences and its function is significantly influenced by immobilization process. Therefore properties of the sensor have to be measured without AChE at first. This process is called input control of the sensor. The reproducibility of electrochemical detector was studied first using hydrogen peroxide and second ferri-ferrokyanide redox couple. Longterm stability and reproducibility of preparation of enzymatic layer were studied. Cell data was evaluated statistically. This article describes measurement on AS and determination properties of electrochemical sensor before immobilization of enzymes by hydrogen peroxide.
Bibliographic citation: In Second IEEE International Conference on Sensors. Toronto: Toronto, 2003. s. 252 (s.) ISBN: 0-7803-8133- 5.

 

INPUT CONTROL OF SENSOR PARAMETERS AND REPRODUCIBILITY OF SENSOR MEASUREMENT
FUJCIK, L., VRBA, R., KREJČÍ, J., HÁZE, J., SKOČDOPOLE, M., SAJDL, O.
Fast detection of pesticide toxicity in the field conditions is very important in many aspects (longtime influence of low concentrations on man´s health, pesticide storage, price of one test etc.). The pesticide concentration measurements are performed on a biosensor with acetylcholinesterase (AChE). The AChE is a very sensitive compound. The measurement uses principle of an artificial synapse (AS) and inhibition of an enzyme Acetylcholinesterase (AChE). The AS is a very effective detector of the pesticide toxicity. Therefore properties of the sensor have to be measured without AChE at first. This process is called input control of the sensor. The reproducibility of electrochemical detector is studied first using hydrogen peroxide and second ferri-ferrokyanide redox couple. The parameters of electrochemical detector itself were evaluated statistically.
Bibliographic citation: IIn XVII IMEKO WORLD CONGRESS. Chorvatsko: 2003. s. 2141 (s.) ISBN: 953-7124-00- 2.

 

 

New Approach in Wide Range Conductivity Measurement with Planar Sensor
HUBÁLEK, J., KREJČÍ, J., KOLAŘÍK, V.
This paper contributes to the field of precise electrolytic conductivity measurements with planar sensors. This novel measuring method was suggested for measurement with comb-like thick-film electrodes. Correction characteristics over a wide range of  specific conductivities were determined from an interface impedance characterisation of the thick-film electrodes. The cell constant strongly depends on the frequency and conductivity of solutions. A local minimum of the imaginary part of the interface impedance is used for corrections to get linear responses. In this minimum a ridge frequency and cell constant were determined for each measured conductivity. An iteration mode of measurements was suggested to exactly measure the conductivity in the ridge frequency in order to achieve a highly accurate response. An implementation of this method as a microcontroller application can used to build-up microsystems for precise conductivity measurements in concentration ranges from 10-6 to 1 M without cell replacement.
Bibliographic citation: In Socrates Workshop 2002 - Proceedings. Intensive Training Programme in Electronic System Design. Chania, Crete (Greece). Ing. Z. Novotny, Brno: FEKT VUT v Brně, 2002. s. 112 (s.) ISBN: 80-214-2217- 3.

 

Wide Range Precise Conductivity Measurement without Cell Replacement.
HUBÁLEK, J., KREJČÍ, J.
The paper presents new approach in the field of precise electrolytic conductivity measurements with planar sensors. This novel measuring method was suggested for measurement with IDEs thick-film electrodes. Correction characteristics over a wide range of  specific conductivities were determined from an interface impedance characterisation of the thick-film IDEs. A local minimum of the imaginary part of the interface impedance is used for corrections to get linear responses. The ridge frequency was determined at wide range of measured conductivity. An iteration mode of measurements was suggested to exactly measure the conductivity in the ridge frequency in order to achieve a highly accurate response. The method takes precise conductivity measurements in concentration ranges from 10-6 to 1 M without cell replacement.
Bibliographic citation: In Eurosensors XVI, The 16th European Conference on Solid- State Transducers. FEL CVUT Praha: Czech Technical University Faculty of Electrical Engineering Department of Measurement Technická 2, Prague 6- Dejvice166 27 Czech Republic, 2002. s. 602 (s.) ISBN: 80-01-02576- 4.

 

 

Precise Conductivity Measurements with Thick- Film IDEs
HUBÁLEK, J., KREJČÍ, J.
Thick-film Pt interdigitated electrodes (IDEs) are used as miniature and cheap chemical sensor for widespread use as conductivity-based transducer. The planar sensor has been characterised by a precise impedance analyser over a wide range of frequencies and conductivities. The frequency characteristics have been studied to describe the electrode behaviour, and for comparison with theory. We found relations between conductivity and frequency. The ridge frequency was detected as suitable measuring frequency to improve accuracy. Extracted relations can be used as correction characteristics. The correction factor was determined for wide range of conductivity to take precise measurements without cell replacement.
Bibliographic citation: In EDS 2002 Electronic Devices and Systems Conference. Brno: Ing. Zdeněk Novotný, CSc., Brno, Ondráčkova 105, 2002. s. 364 (s.) ISBN: 80-214-2180- 0.

 

Iterative Method of Measurements for Chemical sensors
HUBÁLEK, J., KREJČÍ, J., VRBA, R.
The paper contributes to the field of precise electrolytic conductivity measurements with planar sensors. This novel measuring method was suggested for measurement with IDEs thick-film electrodes. Correction characteristics over a wide range of a specific conductivities were determined from an interface impedance characterisation of the thick-film IDEs. The cell constant strongly depends on the frequency and conductivity of solutions. A local minimum of the imaginary part of the interface impedance is used for corrections to get linear responses. In this minimum a ridge frequency and cell constant were determined for each measured conductivity. An iteration mode of measurements was suggested to exactly measure the conductivity in the ridge frequency in order to achieve a highly accurate response. An implementation of this method as a microcontroller application can used to build-up microsystem for precise conductivity measurements in concentration ranges from 10-6 to 1 M without cell replacement.
Bibliographic citation: In EDS 2002 Electronic Devices and Systems Conference. Brno: Ing. Zdeněk Novotný, CSc., Brno, Ondráčkova 105, 2002. s. 369 (s.) ISBN: 80-214-2180- 0.

 

Zařízení pro provádění elektrochemických a biosenzorových měření
Ing. Ilja Krejčí-engineering
 
 

 

Problems with miniaturization of two-electrode system for conductivity measurements.
HUBÁLEK, J., KOLAŘÍK, V.
A sensor miniaturization brings many problems e.g. an effect of the double layer capacitance, a serial resistance of electrodes, a cell constant etc. First results indicate different behaviour of the small-sized electrodes in comparison with the standard large ones. Conductivity measurements need corrections of the cell constant for each type of a liquid solution. Variation of a cell size shows possibilities to find cross relations of all factors. In summary, it is obvious that the Faraday impedance changes character, it means cut-off frequencies of the total impedance frequency characteristics are shifted under a condition variation of measurements. In addition, Wien effect can display for a small inter-electrode distance because high voltage field rises across electrodes as the inter-electrode distance decreases.
Bibliographic citation: In Electronic Devices and Systems Y2K. Proceedings. Brno: Ing. Zdeněk Novotný, CSc., 2000. s. 237 (s.) ISBN: 80-214-1780- 3.

 

Electrical Behaviour of Thin Film Conductometric Sensors
HUBÁLEK, J., KOLAŘÍK, V., KREJČÍ, J
Recently many chemical sensor applications use the thin film technology. Electrode system has had a comb structure. These systems are called interdigitated electrodes (IDES). In most cases good results were achieved using differential or transient measurements. Measurement of frequency characteristics is not possible without correction of cell constant, which is different of the real cell constant. Results of our current research show many problems with the behavioural of chemical cells if the electrode distance is decreased below 1 mm. The cell starts to change its impedance and cell work place is lifted to high frequency. We suppose that both the distance and the shape of IDES influence the frequency characteristic. If the thin-film technology is used for producing IDES, a large resistance is added into results. Our work is based on modelling of a cell behaviour close to electrode and a potential distribution on electrodes.
Bibliographic citation: In Proceeding of 23th IMAPS Conference. Kolobrzeg, PL: 1999. s. 1 (s.)

 

Real Behaviour and Suitable Technology for Interdigitated Electrodes of Chemical Sensors.
HUBÁLEK, J., KOLAŘÍK, V., KREJČÍ, J.
Nowadays, interdigitated electrodes (IDES) are used in many sensor applications. Behaviour of ordinary electrodes was described enough in the literature and expressed as an interface impedance. Cells with a specific distance between electrodes, which is in interval 100mm up to 100mm, exhibit a very different behaviour. This behaviour has an impact on frequency and concentration dependencies of the Warburg impedance. The Warburg Impedance characterizes a diffusion from the bulk of solution to the electrode. This phenomenon has not been described enough until today. This paper investigates how a distance and shape of electrodes and the cell constant influence the interface impedance.
Bibliographic citation: In Proceedings of Conference IMAPS' 99. Harrogate, UK: 1999. s. 234 ( s.)ISBN: 0-9535858-0- 8.

 

Graphite pastes in thick film sensors area.
ADÁMEK M., PRÁŠEK J., KREJČÍ J., FUJCÍK L.
Miniature electrochemical sensors can be produced by thick film technology (TFT). The optimal properties of thick film electrode materials are main problems of sensors design. The optimisation of graphite pastes properties for TFT chemical sensor is discussed. The commercial TFT graphite pastes, which are used for common application, are cheap and easily producible, but they are not efficient for electrochemical measurement. These pastes have insufficient sensitivity and they have other bad properties. Graphite pastes, which were designed for special chemical analysis, are technically known, but these pastes are not workable by screen-printing. The first step in rheological properties addition to graphite electrochemical pastes is the goal of this work. This will ensure the pastes printability that will enable the reproducible mass production.
The graphite powder with paraffin wax mixture is the basic component of common chemical graphite pastes. There were examined different properties of these pastes in dependence on graphite powder and binding material content in this work. Finally there are described some measurement with commercial and specially prepared TFT graphite electrodes. All measurements were done using a standard electrochemical couple of potassium ferrocyanide-ferricyanide.
Bibliographic citation: In Proceedings of Electronic Devices and Systems 1999. Brno, 1999. s. 179-182. ISBN 80-214-1466-9

 

Miniaturization of Conductometric Sensors.
HUBÁLEK, J., KOLAŘÍK, V., KREJČÍ, J.
Nowadays requirements of an analytical chemistry are cheap and precise conductometric sensors with high sensitivity even for very less quantity of a chemical solution. These sensors could be used not only in chemistry but also in other branches of an industry. Realisations of the chemical sensors bring many problems as e.q. an effect of the double layer capacity, the serial resistance of an electrode, the cell constant etc. This paper summarizes the most important problems caused by electrode miniaturization, which were found during research at department of microelectronics.
Bibliographic citation: In Proceedings of Electronic Devices and Systems 1999. Brno: 1999. s. 179 (s.) ISBN: 80-214-1466- 9.