Abstract: A method and optode for determining a concentration of an analyte in a sample liquid is provided. The method comprises a radiation source, where excitation radiation is directed onto a carrier unit which is in contact with the sample liquid and has immobilized molecules of a sensor dye that is sensitive to the analyte. The excitation radiation induces luminescence radiation of the sensor dye. This radiation is detected by a radiation detector, which generates an output signal. The analyte concentration is ascertained from the detector output signal using an evaluation routine. This uses a property of the luminescence radiation on the interaction of the concentration of the analyte in the sample liquid used. The dependence of the examined property of the luminescence radiation on an indirect exchange interaction between the individual molecules of the sensor dye, which interact with each other over particles of the analyte.