Edgar, L.J. et al. Angew. Chem. Int. Ed. Engl. doi:10.1002/anie.201405233 (4 September 2014).

Mass cytometry offers single-cell multiparametric analysis of a much higher order than that of traditional flow cytometry by utilizing high–molecular weight stable isotopes as tags that are read out by inductively coupled plasma mass spectrometry. This avoids the problems of spectral overlap that limit the number of parameters observable by fluorescence-based flow cytometry. Edgar et al. now demonstrate the potential for expanding the applications of this powerful technology to read out results from activity-based probes. They designed a probe for cellular hypoxia, dubbed Telox, by linking 2-nitroimidazole, a reporter for hypoxia, with a tellurium-based mass tag that can be quantified by mass cytometry. They demonstrated that Telox could identify hypoxic tumor cells in a mixture as well as discriminate populations of cells by the amount of tellurium labeling, reflecting differential oxygen exposure.