an efficient way to chemically deliver them into the cytosol of cells. Indeed, current methods (using cell-penetrating peptides for instance) provide very low yields: QDs stay at the plasma membrane or are trapped in endosomes. Here, we introduce a technology based on cell-penetratingpoly(disulfide)s that solves this problem: we deliver about 70 QDs per cell, and 90% appear to freely diffuse in the