Device for detecting and/or determining the concentration of an analyte present in a tissue and a method and use of this device

A device for presence and concentration of an analyte present in a tissue, comprising:

• a sensor being comprised of an interferometer,
• wherein said interferometer comprises an optical fiber arm, having a fiber arm axis, and a binding agent being coated on the arm so as to enable a selective binding of an analyte present in a tissue;
• and
• a guide
• having an input end, a contact end opposite said input end, and a guide axis,
• wherein said guide is comprised of:
• a sidewall being between said input end and said contact end and defining an interior,
• a closed guide face at said contact end,
• a plurality of longitudinal perforations on said sidewalls so as to enable the analyte to reach said binding agent through said guide, and
• an opening at said input end, said interferometer being centrally mounted within said guide through said opening without contacting said sidewall, said fiber arm axis being coaxial with said guide axis, said opening being sealed so as to isolate said interior from surroundings except through said plurality of longitudinal perforations.