Until now, there hasn’t been a general fluorescent dye that scientists could use to stain the material secreted by cells and view it under a confocal microscope. This extracellular material plays a key role in the fate of cells, including stem cell differentiation and cancer progression. Current dyeing methods, including antibody-targeted staining, have been limited to visualizing one component or only certain kinds of tissues. But now a research team led by Jie Shen at Johannes Gutenberg University and Klaus Müllen at Max Planck Institute for Polymer Research, both in Mainz, Germany, has solved this problem by preparing a positively charged macromolecule that fluoresces red when its amine groups bond to negatively charged extracellular material (J. Am. Chem. Soc., DOI: 10.1021/ja8022362). The water-soluble dye is composed of a central perylene chromophore, a polyphenylene dendrimer scaffold, and a polymer shell bearing multiple amine groups. The researchers used the dye to stain fruit fly tissue as well as bovine collagen, finding that the dye is compatible with antibody-based staining. They suggest that their dye could be useful in multiple-channel fluorescence imaging, and they plan to create different analogs for specific biological applications.