Method and apparatus for determining glucose concentration in a biological sample

Glucose-measuring apparatus for the analytical determination of the concentration of glucose in a biological sample, said apparatus comprising:

• a light source for emitting measuring light;
• light-irradiation means having a light aperture by means of which the measuring light is irradiated through a boundary surface of the sample into said sample;
• a primary-side measuring light path from the light emitter to the boundary surface,
• light detection means for detecting light emerging from the sample at a boundary surface after interaction with the sample;
• and
• a secondary-side measuring light path from the boundary surface where the measuring light emerges from the sample to a photodetector,
• wherein a reference light path of defined optical length is provided for guiding light from the light source to the photodetector, and wherein an optic coupler is positioned in the secondary-side measuring light path by means of which the secondary-side measuring light path and the reference light path are combined in such manner that they are incident at the same point on the photodetector, thereby generating an interference signal, said apparatus further comprising
• means for determining the glucose concentration based on a signal provided by the light detection means, wherein a factor in determining the glucose concentration is an optical light path length of the secondary-side measuring light path inside the sample derived from the interference signal.

A method for analytically determining a concentration of glucose in a biological sample, said method comprising the steps of:

• irradiating light along a primary-side measuring light path into the biological sample;
• guiding secondary light emerging from the sample along a secondary-side measuring light path to a photodetector;
• detecting the secondary light with the photodetector, the photodetector providing a signal representative of the secondary light,
• wherein a first portion of the primary light emitted by the light source is guided to the photodetector along a total measuring light path which includes the primary-side measuring light path, an interior light path in which the light travels inside the sample, and the secondary-side measuring light path, wherein a second portion of the primary light emitted by the light source is guided along a reference light path to the photodetector, said reference light path not including an interior light path in which the light travels inside the sample, wherein the optical path length of at least one of the light paths is variable and is set to a plurality of different lengths, wherein the primary-side measuring light path and the secondary-side measuring light path run in a same half-space defined by a boundary surface of the sample, such that the light reflected by the sample enters the secondary-side measuring light path, wherein the light on the reference light path is reflected by a light reflecting optical component in an opposite direction, and wherein the secondary-side measuring light path and the reference light path are combined such that the secondary light and the reference light interfere with each other such that the photodetector detects an interference signal, said method further comprising the step of
• determining the glucose concentration based on the signal provided in the detecting step, wherein a factor in said determining of the glucose concentration is an optical light path length of the interior light path inside the sample derived from said interference signal, wherein said determining step includes setting of a plurality of different relations of the path lengths of the total measuring light path in relation to the reference light path, wherein the optical path length of the reference light path is larger than the sum of the optical path lengths of the primary-side measuring light path and the secondary-side measuring light path, whereby the interference signal corresponds to reflections at different depths in the sample, and determining the glucose concentration from the dependence of the intensity of the interference signal on the set relation of the optical path lengths.