This work aims to develop a photoacoustic-based trace-gas sensor exploiting the sensitivity enhancement provided by a silicon-based cantilever as the acoustic-to-voltage transducer and by its coupling with a custom-made acoustic resonator and a medium-finesse Fabry-Pérot optical cavity. Thanks to the exploitation of a tunable continuous-wave mid-infrared Quantum Cascade Laser, our sensor can simultaneously address N2O and CO roto-vibrational transitions with a detection sensitivity at the part-per-billion level.