Multilayer films and capsules synthesized from DNA are of interest because they are biodegradable, biocompatible, and the structure of the films can be finely controlled by base pairing of the nucleotides. As DNA films are held together through a balance between the attractive hydrogen bonding and the aromatic stacking of the base pairs and the electrostatic repulsion of the negatively charged phosphate backbones, the films can be subject to disintegration at low salt concentrations (<200 mM). Enhancement of the stability of the films is essential if they are to be used in bioapplications. Herein, we describe an approach to form DNA films and capsules that are stable under a variety of buffer conditions, including low salt concentrations (down to 25 mM NaCl). The films are assembled using a triblock oligonucleotide system, in which the two outer blocks facilitate the assembly of the film and the middle block can be used to stabilize the films by hybridizing oligonucleotide sequences that crosslink the films. Additionally, crosslinked DNA capsules are shown to exhibit significantly different shrinkage properties to those of noncrosslinked capsules, thus demonstrating further control over the capsule properties. These DNA capsules are envisaged to find applications as drug-delivery vehicles, in diagnostics, and as microreactors.