A sensor assembly (1) for in-vivo monitoring of a body fluid or tissue (F) comprises: a pressure sensor element (108), comprising a micro- electromechanical system (MEMS) and arranged to detect a pressure of the body fluid or tissue (F) in use and a shield (102), which generally surrounds the pressure sensor element (108) such that the pressure sensor element (108) is within an interior volume of the shield (102), in order to protect and to prevent distortion of the pressure sensor element (108) in use. The pressure sensor element (108) comprises a biocompatible thin film layer (108b), for resisting corrosion and/or fouling of a surface of the pressure sensor element (108) by the body fluid or tissue (F) or biological matter thereof. The pressure sensor element (108) and the shield (102) are in fixed relationship with each other.
