Biosensors are a very useful tool to produce drugs or to monitor chemical species through their product of reaction. The sensor is fabricated bounding on its surface specific enzymes that can accomplish the synthesis function. We studied the possibility to fabricate Si-based micro-biosensors to detect glucose in water solutions. We used porous Si (PS) as surface to bound the glucose oxidase enzyme. We ideated an fabricated a novel biosensor structure based on a PS membrane that can be used for glucose monitoring and for drug production, by properly choosing the enzyme to immobilize in the reactor. The fabrication details of the structure, having a suspended and auto-supporting PS membrane, through surface micromachining processes, ULSI compatible, are shown. Micro channels localised below the membrane will allow the buffer solution flow through the porous matrix. Moreover, in this work we acquired the know-how on the enzyme manipulation, bonding and detection on Si-based surfaces. The glucose oxidase was deposited in PS, on bulk Si and on glass to perform photoluminescence, absorbance and optical microscopy measurements.