Highly sensitive trace-gas sensors are required in a large range of applications, such as biological, environmental, industrial, and fundamental physics. Photoacoustic spectroscopy has the advantages of compactness and robustness and is characterized by a high degree of flexibility in its configuration, in particular in the selection of the laser source and the transducer. Here we report the experimental characterization of new silicon-based Micro electro-mechanical systems (MEMS) structures to be applied as acoustic-to-voltage transducers in a photo-acoustic-based sensor. In our setup, a 4.5 μm continuous wave quantum cascade laser is used to address strong N2O roto-vibrational transition, and the detection of MEMS oscillations is performed via a balanced interferometric readout.