Aviv Regev at the Broad Institute, in Cambridge, uses fluidic systems to separate cells and submits them to detailed genetic analysis, at the rate of thousands per day. The goal is to build a comprehensive cellular human atlas, based on gene expression profiling.

The new technology works instead by cataloguing messenger RNA molecules inside a cell. These messages are the genetic material the nucleus sends out to make proteins. Linnarsson’s method attaches a unique molecular bar code to every RNA molecule in each cell. The result is a gene expression profile, amounting to a fingerprint of a cell that reflects its molecular activity rather than what it looks like.