A device for characterizing a fluid medium with the help of a photoelectric transducer comprises at least one semiconductor substrate possessing at least one space charge zone and presenting a reception surface for receiving the fluid medium in order to constitute an interface between the substrate and the fluid medium, a production system for producing a spot light beam that is amplitude-modulated and that lights at least one zone of the interface through the fluid medium, a measurement system for measuring values of a photoelectric magnitude delivered while performing the lighting so as to create a matrix of values of the photoelectric magnitude, and a processor system for processing values of the photoelectric magnitude delivered by the measurement system and adapted to use the matrix to determine an electronic signature characteristic of the fluid medium.