The factors that limit the performance of the counter-reference electrode in a commercial screen printed biosensor (SPE) for the quantification of glucose i~ whole blood have been investigated. The electrochemistry of this Ag/AgCI SPE is limited by the resistance of the track (R ~ 125 Q). The open circuit potential at long times (equilibrium potential) depends on the activity of cr in the solution following the Nemst equation, meanwhile at short times (t < 100 s) the potential transient recorded from the moment the electrode is immersed in the solutitn showed some anomalous and irreproducible behaviour, probably associated with some nucleation process occurring at the electrode. The cyclic voltammetry showed also a change of slope at low overpotentials (' = -80 mY) due to the different potentials needed to reduce two different kinds ofAgCI particles; those in contact with Ag and those isolated. We have proposed two different types of counter reference electrodes. One type is based in replacing the Ag from the ink with carbon, meanwhile the other one uses the same Ag/AgCI ink, but adding different amounts of KCl. SPEs employing the first approach show potentials more negative than those of the' commercial SPEs due to the increase of the resistance of the track. Also these electrodes are unable to transfer the required charge predicted for the overall sensor in working conditions, so this formulation was discarded. The SPEs loaded with KCI show shorter equilibration times than the commercial electrodes. The potential of the transient part of the curve is very reproducible. During the transient part of the chronopotentiometry, the potential is established by the gradient ofCr created by the dissolution ofthe cr embedded in the ink. Finally, SPEs treated with light and air show an anomalous behaviour compared with fresh SPEs. This negative effect consisted in a shift towards less negative values of the potential recorded in a cathodic galvanostatic experiment. This anomalous behaviour was similar to that produced by oxidising the Ag in the SPE to A~O, but no mechanism that explains this similarity was found. Also SPEs partially oxidised and reduced in cr solutions showed this shift ofthe potential to less negative values. Since this shift means that it is easier to reduce these oxidised and reduced electrodes we believe that the mechanism involve a facilitated nucleation process at the oxidised or reduced electrodes.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:484848 |
| Date | January 2005 |
| Creators | Montequin, Sergio Martinez |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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