A biosensor (1； 1'), comprising: a first structural layer (2； 2') of photodefinible hydrogel； a second structural layer (4； 4') of photodefinible hydrogel； a bioactive region (6； 6'), which extends between the first structural layer (2； 2') and the second structural layer (4； 4') and is made of photodefinible hydrogel including bio-recognition elements and a redox mediator； a working electrode (10； 10'), which extends in direct contact with the bioactive region (6； 6')； a counter-electrode (12； 12'), which extends in direct contact with the first structural layer (2； 2'). The second structural layer (4； 4') has a through opening (8； 8') in the bioactive region (6； 6') so that the bioactive region (6； 6') is in direct fluid connection with an environment external to the biosensor.
