Fig. 2. Quantitative verification of single-strand DNA molecules' selective binding to the end surface of nanorods. (a) Design of an analytical experiment using two samples of nanorods at same weight. The length of the longer rods doubles that of the shorter rods. When both samples are at same weight, the sample of the shorter rods has total end-surface areas nearly twice that of the longer rods. (b) TEM images of 70 nm nanorods and 135 nm nanorods. In a ligand exchange experiment, if DNA molecules only bind to the end surface, the sample of shorter rods should absorb nearly twice the amount of DNA molecules than the longer rods. (c) By checking the amount of residue DNA molecules in suspension, the amount of DNA molecules being capped onto the nanocrystals are quantitatively compared. Scale bar: 100 nm.