Sensor system (70) for detecting a target substance in a reference liquid, comprising a measurement cantilever (71) being functionalized by application of a first coating to one of the measurement cantilever's surfaces, whereby this first coating is sensitive to the target substance. In addition, the system (70) comprises a reference cantilever (72) with a reference coating on one of the reference cantilever's surfaces, whereby this reference coating is less sensitive to the target substance than the first coating. Both cantilevers are arranged such that they can be exposed in a reference step to the reference liquid and in a detection step to the reference liquid with the target substance. A detector unit (73, 74, 83) is employed for determining the difference in the deflection of the measurement cantilever (71) and the reference cantilever (72) during the reference step and the detection step.