Probing interfacial equilibration in microsphere crystals formed by DNA-directed assembly

Abstract

DNA is the premier material for directing nanoscale self-assembly, having been used to produce many complex forms. Recently, DNA has been used to direct colloids and nanoparticles into novel crystalline structures, providing a potential route to fabricating meta-materials with unique optical properties. Although theory has sought the crystal phases that minimize total free energy, kinetic barriers remain essentially unstudied. Here we study interfacial equilibration in a DNA-directed microsphere self-assembly system and carry out corresponding detailed simulations. We introduce a single-nucleotide difference in the DNA strands on two mixed microsphere species, which generates a free-energy penalty for inserting 'impurity' spheres into a 'host' sphere crystal, resulting in a reproducible segregation coefficient. Comparison with simulation reveals that, under our experimental conditions, particles can equilibrate only with a few nearest neighbours before burial by the growth front, posing a potential impediment to the growth of complex structures.

Self-Assembly at a Nonequilibrium Critical Point

“…Assemblies grown at a finite rate possess patterns that are more mixed than the equilibrium one, and at a certain growth rate one encounters a dynamic critical point, beyond which component types mix within the assembly in a manner similar to that of the (anisotropic) equilibrium Ising model above its critical temperature. Our results suggest a way to generate qualitatively defined twocomponent structures using, for instance, DNA-linked colloids [18,19]. Such experiments would serve as a test of the predictions of this paper.…”

“…Because the mobility of particles within solid structures is usually very low (red arrows on figure), such interchange can fail to happen on experimental time scales. The result is a structure whose component types are distributed in a nonequilibrium manner [18][19][20][21][22][23]. Returning to the picture of evolution on a free-energy landscape, one must think of the direction of motion across this landscape as being biased strongly by the underlying microscopic dynamics [22].…”

“…Instead, we need explicit information about the dynamics undergone by components, together with a predictive theory that works "far" from equilibrium. Despite much progress in this direction [13][14][15][16][17][18][19][20][21][22], such a theory does not exist. Here we present evidence suggesting that concepts of nonequilibrium statistical physics may provide a route to a predictive theory of far-from-equilibrium self-assembly.…”

“…The long time scale responsible for such trapping is the slow interchange of component types within solid structures [13][14][15][16][17][18][19][20][21][22][23]. Consider Fig.…”

Direct measurements of DNA-mediated colloidal interactions and their quantitative modeling

“…Moreover, the temperature-dependent stability of such DNA bridges allows the resulting attraction to be modulated (1, 2) from negligibly weak to effectively irreversible over a convenient range of temperatures. Several groups have recently used such interactions to drive the assembly of three-dimensional (3D), crystalline structures from nanoscopic (4)(5)(6)(7)(8) and microscopic (9,10) particles. Ultimately, we envision a highly versatile nanomaterial design protocol in which a user-designed matrix of specific interactions among multiple particle species leads to sequential or even hierarchical assembly of complex particle structures, controlled by a user-designed thermal program.…”