A method for detecting microorganisms on a surface being examined, the method characterized by: attaching (S1) a first free surface side of an oxygen-permeable layer of a sensor foil to at least one portion of the surface being examined with in an airtight sealed manner by the sensor foil blocking re-oxygenation of the oxygen-permeable layer of the sensor foil so that the microorganisms breathe directly into the oxygen-permeable layer of the sensor foil , wherein the oxygen-permeable layer of the sensor foil is doped with an oxygen indicator dye , loaded with oxygen and faces the at least one portion of the surface ; placing (S2) a detection element in relation to the sensor foil exciting (S3) the oxygen indicator dye in the oxygen-permeable layer with an excitation light through an oxygen-impermeable at least partially transparent read-out carrier layer of the sensor foil , the oxygen-impermeable at least partially transparent read-out carrier layer carrying the oxygen-permeable layer ; and detecting (S4) an emission of the oxygen indicator dye when the oxygen indicator dye is in an excited state, the emission being transmitted through the oxygen-impermeable at least partially transparent read-out carrier layer of the sensor foil by the detection element over or after a period of time (t), wherein the received emission of the oxygen indicator dye from the oxygen-permeable layer is indicative of a decrease of oxygen in the oxygen-permeable layer of the sensor foil and thus of a presence and concentration of the microorganisms on the at least one portion of the surface being examined airtight sealed by the sensor foil . attaching (S1) a first free surface side of an oxygen-permeable layer of a sensor foil to at least one portion of the surface being examined with in an airtight sealed manner by the sensor foil blocking re-oxygenation of the oxygen-permeable layer of the sensor foil so that the microorganisms breathe directly into the oxygen-permeable layer of the sensor foil , wherein the oxygen-permeable layer of the sensor foil is doped with an oxygen indicator dye , loaded with oxygen and faces the at least one portion of the surface ; placing (S2) a detection element in relation to the sensor foil exciting (S3) the oxygen indicator dye in the oxygen-permeable layer with an excitation light through an oxygen-impermeable at least partially transparent read-out carrier layer of the sensor foil , the oxygen-impermeable at least partially transparent read-out carrier layer carrying the oxygen-permeable layer ; and detecting (S4) an emission of the oxygen indicator dye when the oxygen indicator dye is in an excited state, the emission being transmitted through the oxygen-impermeable at least partially transparent read-out carrier layer of the sensor foil by the detection element over or after a period of time (t), wherein the received emission of the oxygen indicator dye from the oxygen-permeable layer is indicative of a decrease of oxygen in the oxygen-permeable layer of the sensor foil and thus of a presence and concentration of the microorganisms on the at least one portion of the surface being examined airtight sealed by the sensor foil . <EOS>