| 摘要 |
The system extracts an analyte such as glucose transdermally into reservoirs 22, 24 by reverse iontophoresis using annular electrodes 8,10. The reservoirs comprise hydrogel 22, 24 containing an ionically conducting medium and an enzyme which reacts with the analyte to form hydrogen peroxide, and the concentration of the analyte which results in the reservoir is sub-millimolar. Sensing elements, comprising sensing electrodes 12, 14, reference electrodes, and the annular iontophoresis electrodes 8, 10 sense the hydrogen peroxide electrochemically and produce a signal related to analyte concentration. The sensing electrodes have an area of 0.1 - 3 cm<2>, a background current from 2 - 60 nA, and a sensitivity of 6 - 180 nA/ÁM of hydrogen peroxide in a buffer solution at 0.6 V. The iontophoresis electrodes have an area of 0.3 - 1.0 cm<2> and are capable of repeated cycles of current in the range 0.01 - 1.0 mA/cm<2>.
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