D'Astolfo, D.S. et al. Cell 161, 674–690 (2015).

The direct delivery of a protein into eukaryotic cells allows scientists to study its function without resorting to genetic manipulation. However, existing methods are inefficient or require the protein to be tagged with a cell-penetrating peptide. D'Astolfo et al. describe a method called induced transduction by osmocytosis and propanebetaine (iTOP) for the delivery of native proteins and other compounds into cells. In iTOP, cells are mixed with the protein of interest and a special buffer containing sodium chloride and nondetergent sulfobetaine 201. Upon incubation, the protein is efficiently delivered to cells in a concentration-dependent manner. The authors demonstrated the method in multiple cell types, including stem cells, and used it to deliver Cas9 and a guide RNA to demonstrate gene targeting without exogenous gene expression.