Herein, we demonstrate that it is possible to design a sensor array with one multivalent cationic receptor (a dendrigraft of lysine) and one fluorescent anionic indicator (a fluorescein-labeled peptide). Depending on the loading of the indicator on the receptor, negatively charged glycosaminoglycans (GAGs) induce a positive or negative variation of the fluorescent signal as they displace the indicators from the receptor or they compact the indicators on the receptor's surface, respectively. This unique strategy allows not only the blind identification of pure GAGs with a level of accuracy of 100%, but also the differentiation of mixtures.