Sensor for the optical detection of free hemoglobin (96) in a whole blood sample (99), the sensor comprising a translucent slab (2) with a front side (3) and a back side (4) facing away from the front side (3), wherein the front side (3) is adapted for being contacted with a whole blood sample (99)； a reflective layer (5) at the front side (3) of the translucent slab (2), the reflective layer (5) being adapted to reflect light reaching the reflective layer (5) from the translucent slab (2)； an optical probing device comprising a light source (10) and a detector (20), wherein the light source (10) is adapted to illuminate at least pores in the translucent slab, wherein the detector (20) is arranged to receive light (21) emerging from the pores (6) in response to an illumination (11) by the light source (10), and wherein the detector (20) is adapted to generate a signal representative of the detected light. The translucent slab (2) is provided with dead-end pores (6) extending from the front side (3) into the translucent slab (2) in a direction towards the backside (4). Each of the pores (6) has a respective opening (7) in the front side (3) of the translucent slab (2) penetrating the reflecting layer (5). A cross-sectional dimension of the openings (7) of the pores (6) is dimensioned so as to prevent red blood cells (98) from entering the pores (6), while allowing free hemoglobin (96) to enter the pores (6).
