Nanoparticle Crystallization Driven by Competitive Toehold-Mediated DNA Strand Exchange Reactions

DNA-mediated colloidal crystal engineering offers a powerful route for constructing three-dimensional nanoparticle superlattices with programmable structures and properties. However, achieving room-temperature fabrication of DNA-bonded colloidal crystals with long-range order remains challenging because nanoparticle assemblies are often kinetically trapped in metastable states. Here, we present a simplified enthalpy-regulation strategy based on a toehold-exchange mechanism to control interactions between DNA-functionalized gold nanoparticles. By tuning the relative lengths of the forward and reverse toeholds and the concentration of a DNA trigger, nanoparticle aggregation kinetics are precisely regulated, enabling a symmetric binary system to circumvent kinetic trapping and assemble into high-quality BCC superlattices. We further extend this approach to an asymmetric binary system, where selective control of linker valence directs the formation of distinct CsCl and AlB2 superlattices. Owing to its simplicity and adaptability, this strategy provides a versatile platform for integrating diverse DNA circuits with colloidal crystal assembly and engineering programmable phase behaviors.