A sensor structure for sensing the concentration of at least one given species in a liquid medium including: - a support, - at least one waveguide, - at least one optical resonator hanging on the support, said optical resonator being optically coupled to the waveguide so that the waveguide injects into the optical resonator an electromagnetic wave and collects said electromagnetic wave coming out of the waveguide, said optical resonator comprising an optical active area for the circulation of the electromagnetic wave, and - at least one mechanical resonator hanging on the support, said mechanical resonator and said optical resonator being coupled, said mechanical resonator being configured to vibrate in a volume mode and including at least one face extending in the plane of the sensor and configured to receive molecules of said given species, wherein the optical resonator includes a body comprising the optical active area, said body comprising a first face (C.1) and a second face, the second face facing the support and the first face (C.1) being oriented away from the support, said optical resonator also including an optical isolation layer deposited at least over the first face (C.1) at least in line with the optical active area so as to confine at least partially the electromagnetic wave in the body, the concentration sensor structure, intended to be immersed in a liquid medium, further comprising a functionalization layer, configured to capture the at least one given species of which the concentration in the liquid medium is desired, and covering the optical isolation layer, the functionalization layer and the optical isolation layer being either directly in contact or separated by an adhesion layer, wherein the optical resonator and the mechanical resonator are the same element suspended from the support, the first face forming the face configured to receive molecules, said element being an opto-mechanical resonator. - a support, - at least one waveguide, - at least one optical resonator hanging on the support, said optical resonator being optically coupled to the waveguide so that the waveguide injects into the optical resonator an electromagnetic wave and collects said electromagnetic wave coming out of the waveguide, said optical resonator comprising an optical active area for the circulation of the electromagnetic wave, and - at least one mechanical resonator hanging on the support, said mechanical resonator and said optical resonator being coupled, said mechanical resonator being configured to vibrate in a volume mode and including at least one face extending in the plane of the sensor and configured to receive molecules of said given species, wherein the optical resonator includes a body comprising the optical active area, said body comprising a first face (C.1) and a second face, the second face facing the support and the first face (C.1) being oriented away from the support, said optical resonator also including an optical isolation layer deposited at least over the first face (C.1) at least in line with the optical active area so as to confine at least partially the electromagnetic wave in the body, the concentration sensor structure, intended to be immersed in a liquid medium, further comprising a functionalization layer, configured to capture the at least one given species of which the concentration in the liquid medium is desired, and covering the optical isolation layer, the functionalization layer and the optical isolation layer being either directly in contact or separated by an adhesion layer, wherein the optical resonator and the mechanical resonator are the same element suspended from the support, the first face forming the face configured to receive molecules, said element being an opto-mechanical resonator.