According to the present invention there is provided an optical sensor component (100) for use in an optical sensor for monitoring of protease activity in wound fluid, the optical sensor component comprising, a sensing optical fiber (1) comprising an unmodified portion (2) and a modified portion (3). The modified portion (3) is an uncladded portion (3), or the core of the optical fiber (1), and comprises a coating (4) having a dye (5) which is configured to absorb light, the coating (4) being configured such that it has a predetermined sensitivity to protease such that the coating (4) degrades upon contact with protease, wherein degradation of the coating decreases the amount of light which can be absorbed in the sensing optical fiber (1). There is further provided a corresponding method of detecting protease activity, and an optical sensor device and a wound dressing which comprises the optical sensor component. There is further provided a method of preparing the optical sensor component.
