The invention relates to whole-cell sensors for monitoring bioavailable nitrogen, phosphorus and sulphur, individually or in at least one combination in a medium, and to the use thereof. The whole-cell sensors consist of genetically modified yeast cells which are immobilised in a xerogel matrix and contain at least one marker gene controlled by a promoter of a gene, the transcription of said gene being significantly increased or reduced in the absence of nitrogen, phosphorus or sulphur, and the yeast cells are at least coupled to a signal detector.