Sensor, method for detecting the presence and / or concentration of an analyte using the sensor and use of the method

A sensor comprising at least one sensing element (1), preferably a plurality of sensing elements, the at least one sensing element (1) comprising a resonant cavity device (2) for emitting optical radiation at an operation wavelength, the resonant cavity device (2) comprising a first mirror (12) at a first side and a second mirror (11) at a second side opposite to the first side (12), characterized in that the second mirror (11) comprises a structured layer (13) supporting surface plasmon resonance and in that the at least one sensing element (1) further comprises a sensing layer (30) overlaying the second mirror (11) and provided over the structured layer (13), the sensing layer (30) being provided for exposure to an analyte and having a refractive index which changes upon absorption or adsorption of the analyte, resulting in a change of power of the optical radiation, and detection means (20) for detecting the change of power of the optical radiation.