Described are peptides for delivery of a nanoparticle to the cytosol, the peptide comprising: (a) a nanoparticle association domain; (b) a proline-rich spacer domain; (c) an uptake domain; and (d) a vesicle escape domain comprising a non-hydrolyzable lipid moiety, wherein the spacer domain is between the nanoparticle association domain and the uptake and vesicle escape domains, and wherein the peptide, when attached to an extracellular nanoparticle, is effective to induce uptake of the nanoparticle by a cell and delivery of the nanoparticle to the cytosol of the cell. Also described are methods of delivery of a nanoparticle to the cytosol of a cell, the method comprising providing to a cell a nanoparticle attached to such a peptide. Exemplary nanoparticles include quantum dots.