The invention is a device and method for detecting an analyte in a medium. An exciting light source produces an exciting light wave, which propagates to the medium and heats the latter. The device comprises a transducer for detecting the heating of the medium. According to one embodiment, the transducer is a thermal transducer, configured to detect a variation in the temperature of the medium. According to another embodiment, the transducer is an acoustic transducer, configured to detect a photoacoustic wave propagating from the medium. Whatever the embodiment, the transducer employs a membrane, on which a waveguide is placed. The waveguide comprises a resonant optical cavity. Transduction is achieved by analyzing a variation in a resonant wavelength of the optical cavity.