Method for determining a concentration of an analyte in a sample liquid, in which, a) by means of a radiation source (3, 10, 17, 25, 31), excitation radiation is directed onto a carrier unit (5, 13, 20, 26, 33) which is in contact with the sample liquid and which has immobilized molecules of a sensor dye that is sensitive to the analyte, wherein the mean distance R between immobilized molecules is smaller than the Förster radius r 0, b) a portion of sensor dye luminescence radiation, the sensor dye luminescence radiation being induced by the excitation radiation, is applied to a radiation detector (4, 14, 21, 28, 34, 35) in order to generate a detector output signal therefrom, and c) an evaluation routine determines the analyte concentration from the detector output signal, wherein a dependence of a property of the luminescence radiation on the concentration of the analyte in the sample liquid is used, characterized in that d) for determining the analyte concentration, the dependency of the property of the luminescence radiation being examined on an indirect exchange interaction between the molecules of the sensor dye with one another is exploited, wherein the indirect exchange interaction occurs when the molecules of the sensor dye interact with the particles of the analyte and e) that the evaluation routine evaluates a variable that is proportional to an exponential function exp R r − r o wherein R is a measure of a distance between the immobilized molecules of the sensor dye, r is a measure of the distance between the molecules of the analyte that interact with a molecule of the sensor dye, and r 0 is the Förster radius. a) by means of a radiation source (3, 10, 17, 25, 31), excitation radiation is directed onto a carrier unit (5, 13, 20, 26, 33) which is in contact with the sample liquid and which has immobilized molecules of a sensor dye that is sensitive to the analyte, wherein the mean distance R between immobilized molecules is smaller than the Förster radius r 0, b) a portion of sensor dye luminescence radiation, the sensor dye luminescence radiation being induced by the excitation radiation, is applied to a radiation detector (4, 14, 21, 28, 34, 35) in order to generate a detector output signal therefrom, and c) an evaluation routine determines the analyte concentration from the detector output signal, wherein a dependence of a property of the luminescence radiation on the concentration of the analyte in the sample liquid is used, characterized in that d) for determining the analyte concentration, the dependency of the property of the luminescence radiation being examined on an indirect exchange interaction between the molecules of the sensor dye with one another is exploited, wherein the indirect exchange interaction occurs when the molecules of the sensor dye interact with the particles of the analyte and e) that the evaluation routine evaluates a variable that is proportional to an exponential function exp R r − r o wherein R is a measure of a distance between the immobilized molecules of the sensor dye, r is a measure of the distance between the molecules of the analyte that interact with a molecule of the sensor dye, and r 0 is the Förster radius. wherein R is a measure of a distance between the immobilized molecules of the sensor dye, r is a measure of the distance between the molecules of the analyte that interact with a molecule of the sensor dye, and r 0 is the Förster radius.