The invention relates to measuring the concentration of analytes with the
aid of an oxidase in an immersion sensor situated in a fluid or in a
matrix containing fluid. Oxygen diffuses into the enzyme layer from
within, from a gas-filled space connected to the atmosphere and/or to an
oxygen reservoir. This enables oxygen saturation of the oxidase in a
low-oxygen or oxygen-free medium and/or at high analyte concentrations.
The analyte diffuses into the enzyme layer in a channel or a number of
channels which contain(s) water and limit(s) diffusion, wherein the
channel/channels on the surface of the sensor is/are filled with a
protein-impermeable, hydrophilic matrix. By increasing the channel
cross-section on the surface of the sensor and/or by connecting the
channel/channels to a protein-impermeable, porous, hydrophilic layer on
the surface of the sensor, the effect of outer deposits on the diffusion
resistance of the analyte is reduced.