This paper presents an original piezoresistive strain gauge architecture based on two polysilicon layers able to sense in-plane strain. These gauges are electrically isolated from the external environment in order to be used in liquids. The presented design is based on three optimization keypoints, which one of these allows the reduction of the beam width thus leading to an increased sensitivity in force. Design, modelling, fabrication and characterization have been investigated. An in-plane sensitivity of 30x10 -6 μN -1 has been obtained which is comparable to out of plane sensitivity, typically obtained with AFM cantilevers