In this paper the novel method of calibration of glucose amperometric type sensor implemented in an integrated microdialysis based micro system is presented. This method consists in evaluation of the charge, resulting from the glucose consumption in the enzymatic reaction, transferred to the electrode under stop-flow conditions

Bergveld, P.

Olthuis, W.

Pijanowska, D.G.

Sprenkels, A.J.

English

University of Twente Research Information

METHOD OF CALIBRATION OF GLUCOSE SENSORIMPLEMENTED IN AN INTEGRATED MICRODIALYSISBASED SYSTEMD.G. Pijanowska1,2, A.J. Sprenkels2, W. Olthuis2, P. Bergveld21 Institute of Biocybernetics and Biomedical Engineering, PAS, Warsaw, POLAND,2 MESA+ Research Institute, University of Twente, Enschede, THE NETHERLANDSABSTRACTIn this paper the novel method of calibration of glucose amperometric type sensorimplemented in an integrated microdialysis based micro system is presented. This methodconsists in evaluation of the charge, resulting from the glucose consumption in theenzymatic reaction, transferred to the electrode under stop-flow conditions.Keywords: Calibration, electrochemical sensors, lab-on-a-chip, microdialysis1. INTRODUCTIONMicrodialysis is an on-line sampling technique used for in-vivo monitoring. Thistechnique is based on a size-selective diffusion of the analyte through a semi-permeablemembrane so that, the dialysate is a macromolecule–free sample ready for analysis withoutany pretreatement. Microdialysis is performend with use of a microdialysis probe,consiting of a dialysis tube, coupled with an appropriate analyzer. The connection betweenthe microdialysis probe and the analyzer introduces a certain lag time in analysis.To minimize the lag time, a miniaturized microdialysis based system has beendeveloped [1]. The integrated microdialysis system consists of several functional blocks:microdialysis probe, electrochemical sensor array and calibration facility.Although, principles of analytical chemistry encompass methods of sampling as well asmeasurement including calibration of detectors, the calibration procedure still causesproblems espacialy in same cases e.g. on-line and in-vivo monitoring.A novel method of calibration of glucose sensor implemented in an integratedmicrodialysis based micro system has been developed. The calibration method consists inevaluation of the charge, resulting from the glucose consumption in the enzymatic reaction.2. THEORYAs a model, an enzynmatic reaction of an oxidase enzyme is considered where thesubstrate is oxidized by the enzyme in the presence of co-substrate (oxygen) and hydrogenperoxide is produced. The transduction of the enzymatic reaction is achivedamperometrically then, the current response is related to the hydrogen peroxide flux to theworking electrode. One-dimentional mass transfer to an electrode is described by theNernst-Planck equation [2]:)()()()()()( xVxCxxxCDRTFzxxCDxJ jjjjjjj(1)where Jj is a flux of species j at distance x from the electrode, Dj is a diffusion coefficientfor j, V – velocity, zj – valency, xxCj )( and xx)( are concentration and potentialgradients at distance x from the electrode respectively.9th International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 9-13, 2005, Boston, Massachusetts, USA470 0-9743611-1-9/µTAS2005/$20©2005TRF9th International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 9-13, 2005, Boston, Massachusetts, USA471When the convection mass transport is absent and the migration is negligible, thecurrent at the working electrode is the following:jJAFni (2)where Jj is the diffusion dependend flux of species j, n - number of transfered electrons, F -the Faraday constant and A - the electrode area.Mass of the substrate (m) and a number of the substrate particles (np) consumed in theenzymatic resulting in the charge transferred to the electrode ( ) are the following:idtidtAvneMm mol (3)idtnen p1 (4)where Mmol – molar mass, e – charge of an electron and Av – the Avogadro number.An effect of the substrate depletion can be observed under specific circumstances, inparticular when the volume of the sample is comparable or smaller than the reaction spaceof the enzymatic biosensor. Then, based on a charge transferred at the electrode, the totalamount of the substrate as well as number of the substrate particles present in the samplesolution can be calculated. Under the condition of well defined plug of a calibrant (thesubstrate concentration, volume), this approach can be used for the sensor calibration. Italso reveals potential of electrochemical sensors utilization in nano range analysis (eq. 4).3. EXPERIMENTALThe integrated microdialysis system was realized in a silicon-glass sandwich technology(Fig. 1.a). The microdialysis probe and flow-through electrochemical sensor array wereformed by fixing of a dialysis tube (ID 200 µm, from regenerated cellulose, MWCO20 kD).(a)perfuzatesemipermeable capillarydialyzatemicrodialysis probe- Pt electrodePyrex- Ag/AgClamperometric sensor10 mmP1 P2WEREcalibration facilitysensor arrayCE(b)semipermeable capillary, ID = 200 umsampleWEREreaction cell (GOx)CELFigure 1. Layout of the microdialysis system (a) and geometry of the senosor cell (L=18 mm) (b).The amperometric sensor and the built-in calibration facility based on dual-pumpelectrochemically actuated microdosing system have been described previously [3,4].The reaction cell of the sensor (Fig.1.b) was filled with enzyme - glucose oxidase typeII (GOx) - solution of concentration of 8 mg/ml. Volume of the reaction cell was around5 µl while volume of sample passing through the sensor along the semipermeable tube was50 nl. The sample was transported at a flowrate 2 µl/min. When it reached the sensor, theflow was stoped till the whole amount of the glucose was consumed.4. RESULTS AND DISCUSSIONUnder flow conditions the decay of the current peak results from the sample transportalong the sensor and sample dispersion, while in the case of the stop-flow conditions theFigure 1: schematic depiction ofnano-porous electrode system9th International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 9-13, 2005, Boston, Massachusetts, USA472observed decay of the current peak results from the effect of glucose depletion in the sample due to its consumption in the enzymatic reaction. Since our device had relatively large reaction cell (5µl), the effect of glucose depletion in 50 nl sample stoped in the sensor passage was observed.-90-80-70-60-50-40-30-20-1000 2000 4000 6000time [s]Id [nA]Figure 3. Response of the flow-trough amperometric sensor for samples of different glucose concentration 12.5, 25 and 6.25 mM. Based on the experimental data (Fig.3) the mass of glucose consumed in the enzymatic reaction under stop-flow condition was calculated according to equation (3). These results are in close agreement with the apparent mass of glucose contained in the calibration plugs of 50 nl volume and different initial concentrations (12.5, 25 and 6.25 mM). The apparent glucose concentration in the plugs was corrected for dispersion caused by the plugs transport to the sensor space. The dispersion was calculated according to the Vanderslice formula [5]. Since the charge is calculated for the current peak from baseline-to-baseline, to evaluate sensor sensitivity only one calibrant is used.  5. CONCLUSIONS  A novel approach to calibration of amperometric type sensors was developed. The method is based on the effect of glucose consumption in the enzymatic reaction performed under stop-flow conditions. The calibration is applicable for on-line monitoring. REFERENCES[1] A.J. Sprenkels, W. Olthuis, P. Bergveld, On the integration of a microdialysis-based µTAS with calibration facility on a silicon-glass sandwich, The 1st Ann. Int. IEEE-EMBS Spec. Topic Conf. on Microtechnologies in Med. and Biology, Oct. 12-14, 2000, Lyon, France, pp. 326-330, (2000). [2] A.J. Bard, L.R.Faulkner, Electrochemical methods, Wiley, NY, (1980). [3] S. Böhm, D. Pijanowska, W. Olthuis, P. Bergveld, A flow-through amperometric sensor based on dialysis tubing and free enzyme reactors, Biosens. and Bioelectr., 16, pp.391-397, (2001). [4] A.J.,Sprenkels, D.G.,Pijanowska, J.G. Bomer, S.,Herber, K.M. van Delft, W.,Olthuis, P.,Bergveld, A closed-loop calibration system for a microdialysis-based lab-on-a-chip,Proc. of the 6th Conf. on Miniaturized Chemical and Biochemical Analysis Systems, µTAS 2002, Nov. 4-7, 2002, Nara, Japan, Vol. 2, pp. 670-673, (2002). [5] J.T. Vanderslice, K.K. Stewart, A.G. Rosenfeld, D.J. Higgs, Laminar dispersion in flow-injection analysis, Talanta, 28, pp. 11-18, (1981).   

Method of calibration for glucose sensor implemented in an integrated microdialysis based system

A closed-loop calibration system for a microdialysis-based lab-on-a-chip,

A flow-through amperometric sensor based on dialysis tubing and free enzyme reactors,

L.R.Faulkner, Electrochemical methods,

Laminar dispersion in flow-injection analysis,

On the integration of a microdialysis-based µTAS with calibration facility on a silicon-glass sandwich,

http://purl.utwente.nl/publications/76599

Method of calibration for glucose sensor implemented in an integrated microdialysis based system

Abstract

Similar works

Full text

Available Versions

University of Twente Research Information