The invention relates to a transducer device (100,200,300,400) for detecting an environmental state or a change in the environmental state, in particular for detecting an environmental state within a biological material. The transducer device (100,200,300,400) comprises a channel (2,22,51) comprising a fluid, a hydrogel material (1,21,51), which is adapted to change its volume when getting into contact with an environmental material and/or when detecting an environmental change, and which is mechanically coupled to the channel (2,22,51) such that the volume of the channel (2,22,51) changes when the volume of the hydrogel material (1,21,51) changes. The transducer device (100,200,300,400) further comprises a sensor (11,12,25,35), which is adapted to generate a signal upon detection of the change of a physical property of the fluid that is induced by the volume change of the channel (2,22,51). By applying the transducer device (100,200,300,400) according to the invention within a bodily lumen, an accurate monitoring of physiological parameters, for which the hydrogel material (1,21,51) is sensitive, within the bodily lumen is possible. It is also possible to apply the transducer device (100,200,300,400) outside of the bodily lumen, for example to monitor the blood of a patient outside the bodily lumen.