A porous mirror (1) for detection of an analyte (96) in a fluid (99) by optical probing, comprising a translucent slab (2) with a front side (3), and a backside (4) facing away from the front side (3), wherein the front side (3) is adapted for being contacted with a fluid (99), and 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 from the backside (4) of the translucent slab (2), wherein the translucent slab (2) comprises pores (6), wherein the pores (6) are dead end pores (6) extending from respective openings (7) at the front side (3) into the translucent slab (2), through the reflective layer (5), wherein a cross-sectional dimension of the openings (7) of the pores (6) is dimensioned so as to prevent larger particles or debris, if any included the fluid, from entering the pores (6), while allowing the analyte (96) in the fluid (99) to enter the pores (6) via diffusion.