Loop-functionalized peptoid nanosheets. Peptoid sequences that contain a specific pattern of polar and hydrophobic residues, form extended supramolecular two-dimensional nanosheet assemblies. The nanosheets can be functionalized with loops by inserting a short stretch of amino acids into the peptoid during the solid-phase peptoid synthesis. During the assembly, the loop inserts get excluded from the packing of the hydrophobic core and are displayed on the aqueous surface of the nanosheet. Inset: Atomic force microscopy of a peptoid nanosheet, demonstrating their extreme aspect ratio.