A device for detecting at least one substance of a fluid, has a piezoacoustic thin film resonator with a piezoelectric layer on which electrode layers are arranged, and an adsorption surface for adsorbing the fluid substance, wherein the piezoelectric and electrode layers and the adsorption surface are designed and arranged on each other such that by electrically activating the electrode layers, an excitation alternating field can be coupled into the piezoelectric layer. The thin film resonator can be excited to a resonance oscillation frequency fR which depends on an amount of the substance adsorbed on the adsorption surface because of an excitation alternating field coupled into the piezoelectric layer. An electrical insulating layer is arranged directly on a side of one of the electrode layers facing away from the piezoelectric layer. Particularly advantageous is the combination of an aluminum electrode layer and a silicon dioxide insulating layer.