Method for measuring the concentration or change in concentration of a redox-active substance and corresponding device
In order to follow the change in concentration of a redox-active substance, potential suitable for a reducing process or oxidation process are applied to the working electrode of a measuring device. The potential of the working electrode is pulsed and measuring phases and relaxation phases are alternately produced, the pulse lengths of the measuring phase and relaxation phase being predetermined in a suitable manner. In this manner, a rapid relaxation of the concentration gradient is forced electrochemically so that the measurement can be carried out on simple transducer arrays. The device includes a transducer array in addition to a suitable potentiostat. The transducer array may include a planar metal substrate on which at least one flexible insulator having a firm connection between the metal surface and the insulator surface is located. The array is generated by suitably structuring the substrate.
1. A method for measuring at least one of a concentration and change in concentration of a redox-active substance as a mediator in a molecular-biological detection system, in which as a result of application of suitable potentials to a working electrode, at least one of a reduction process and an oxidation process takes place as a redox reaction, the method comprising:
measuring an oxidation current to obtain a measuring phase;
measuring a reduction current to obtain a relaxation phase;
pulsing the potential of the working electrode, and alternately forming the measuring phases and the relaxation phases;
selecting measuring-phase pulse lengths so that, at the end of the pulse, a capacitive current is small in comparison with a Faraday current; and
selecting relaxation-phase pulse lengths so that, at the end of the pulse, a concentration gradient is relaxed such that at a beginning of a following measuring phase, the change in concentration of the mediator, brought about by the measurement of the mediator, is reversible.
2. The method according to claim 1 , wherein a current, measurable at the end of the measuring phase, forms the measuring signal.
3. The method according to claim 1 , wherein the potentials are selected so that the reactions occur in a diffusion limiting current range.
4. The method according to claim 1 , further comprising:
measuring at least one of a concentration and change in concentration of a redox-active substance as a mediator, in a molecular-biological detection system, using the selected pulse lengths.
5. The method according to claim 1 , wherein, when measuring the reduction current, an oxidation potential is set during the relaxation phase and the species reduced during the measuring phase and still located in front of the working electrode are oxidized again.
6. The method according to claim 5 , wherein the pulsed redox-cycling is carried out with set pulse shapes.
7. The method according to claim 6 , wherein the pulsed redox-cycling is carried out with at least one of a rectangular, triangular and sinusoidal course.
8. The method according to claim 1 , wherein the relaxation phase is at least as long as the measuring phase.
9. The method according to claim 8 , wherein the relaxation phase is longer than the measuring phase.
10. The method according to claim 9 , wherein, with a repetition rate of 1 Hz, the pulse lengths of the measuring phases amount to 100 to 300 ms, and the relaxation phase amounts to between 700 and 900 ms.
11. The method according to claim 9 , wherein, with a repetition rate of 1 Hz, the pulse lengths of the measuring phases amount to 250 ms, and the relaxation phase amounts to 750 ms.
12. The method according to claim 1 , wherein, when measuring the oxidation current, a reduction potential is set during the relaxation phase and the species oxidized during the measuring phase and still located in front of the working electrode are reduced again.
13. The method according to claim 12 , wherein the repetition rate for the pulsed redox-cycling amounts to at least 1/10 Hz.
14. The method according to claim 12 , wherein the repetition rate for the pulsed redox-cycling amounts to at least 1/10 Hz.
15. The method according to claim 12 , wherein the pulsed redox-cycling is carried out with set pulse shapes.
16. The method according to claim 15 , wherein the pulsed redox-cycling is carried out with at least one of a rectangular, triangular and sinusoidal course.