The present disclosure relates to an optical sensor having a light source that emits light on a sensor layer, wherein the sensor layer can be brought into contact with a medium, wherein the first sensor layer emits emission light as a function of the incident light and a concentration of a measured value of the medium; a receiver, which receives the emission light; a first light guide, which conducts light from the light source onto a first region of the sensor layer and conducts emission light from the first region of the sensor layer to the receiver; and a second light guide independent of the first light guide which conducts light from the light source onto a second region of the first sensor layer and conducts emission light from the second region of the sensor layer to the receiver.