Binary Superlattice Design by Controlling DNA-Mediated Interactions

Abstract

Most binary superlattices created using DNA functionalization or other approaches rely on particle size differences to achieve compositional order and structural diversity. Here we study two-dimensional (2D) assembly of DNAfunctionalized micron-sized particles (DFPs), and employ a strategy that leverages the tunable disparity in interparticle interactions, and thus enthalpic driving forces, to open new avenues for design of binary superlattices that do not rely on the ability to tune particle size (i.e., entropic driving forces). Our strategy employs tailored blends of complementary strands of ssDNA to control interparticle interactions between micron-sized silica particles in a binary mixture to create compositionally diverse 2D lattices. We show that the particle arrangement can be further controlled by changing the stoichiometry of the binary mixture in certain cases. With this approach, we demonstrate the ability to program the particle assembly into square, pentagonal, and hexagonal lattices. In addition, different particle types can be compositionally ordered in square checkerboard and hexagonal -alternating string, honeycomb, and Kagome arrangements. The field of DNA-mediated particle assembly has undergone remarkable progress over recent years (1), owing, at least in part, to its potential as a powerful platform for rational, bottomup design and engineering of complex materials, and motivated by recent successful translations into applications as diverse as sensing (2), photonics (3), and catalysis. The growing number of synthetic pathways and design strategies to fabricate DNA-functionalized particles (DFPs) has led to the development of a diverse palette of tailorable building blocks from which to choose, comprised of particles of a wide range of inorganic to organic compositions, a near continuum of particle sizes spanning nanometers to micrometers, precise DNA sequence control and thus tailorable hybridization, diverse chemistries for DNA grafting/association, and fine tunability of the grafting density. (4)(5)(6) Accompanying this expanding diversity of building blocks has been a parallel development of specific to generalized design principles that have begun to link molecular-scale DFP function with mechanisms of assembly and the resulting uni-or multi-modal crystalline structures.To this end, the growing combination of theory, simulations, and experiments, has helped to overcome some of the challenges in the field. For example, re-entrant melting strategies (7,8) have been successfully developed to alleviate the very narrow temperature ranges for efficient crystallization of DFPs.The most common route to induce attraction between DFPs, and thus program their assembly, leverages the direct or indirect (i.e., with additional DNA linker strand) hybridization of complementary DNA strands tethered separately to two types of particles. Under suitable conditions in such systems, particles with complementary DNA functionality (i.e., 'unlike' particles) form attractive contacts among multiple strands of h...

Entropy Stabilizes Floppy Crystals of Mobile DNA-Coated Colloids

“…By using DNA-coated colloids (DNACCs), a number of ordered crystals [4-10] and selfassembled "colloidal molecules" [11] have been obtained in experiments, while the self-assembly mechanism of DNACCs is still not well understood [9,12,13]. For example, the diffusionless transformation from a floppy crystal to the other compact crystal has been observed in experimental systems while the underlying mechanism remains not fully resolved [13].Recently, a novel system of mobile DNA-coated colloids (mDNACCs) was introduced that displays qualitatively new properties [14,15]. Compared with immobile DNA-coated colloidal systems, mDNACCs have a broader temperature window for self-assembly, and therefore allow the better control over the assembly process [14].…”

“…By using DNA-coated colloids (DNACCs), a number of ordered crystals [4-10] and selfassembled "colloidal molecules" [11] have been obtained in experiments, while the self-assembly mechanism of DNACCs is still not well understood [9,12,13]. For example, the diffusionless transformation from a floppy crystal to the other compact crystal has been observed in experimental systems while the underlying mechanism remains not fully resolved [13].…”

“…These ssDNA tails serve as "sticky ends" that bind specifically to other colloids coated with ssDNA tails of complementary sequence, which offers a novel way of manipulating the self-assembly of colloidal particles [2,3]. By using DNA-coated colloids (DNACCs), a number of ordered crystals [4][5][6][7][8][9][10] and selfassembled "colloidal molecules" [11] have been obtained in experiments, while the self-assembly mechanism of DNACCs is still not well understood [9,12,13]. For example, the diffusionless transformation from a floppy crystal to the other compact crystal has been observed in experimental systems while the underlying mechanism remains not fully resolved [13].…”

“…Then using βU = βF att + βF rep above, we perform extensive Monte Carlo simulations for systems of N ≈ 500 mDNACCs; and by free energy calculations [21], we construct the phase diagrams in both 2D and 3D. In our 2D system of mDNACCs, colloids are moving in a 2D plane while DNA linkers rotate in a 3D space, which can model the selfassembly of mDNACCs at the bottom of an experimental chamber [13,14] or the liquid-liquid interface [22]. Figure 1 shows phase diagrams in the area/packing fraction η -binding strength β∆G 0 representation for mDNACC systems in 2D and 3D, respectively.…”

“…And for a binary system of colloids coated with very short DNA linkers, it has been mentioned that the CsCl structure is favored over the CuAu structure by virtue of its higher vibrational entropy [6]. Despite these examples, stabilization mechanisms for floppy crystals are largely undistinguished for DNACCs [9,13,24,28]. For this case, to explore the stabilization mechanism for the floppy crystals in mD- NACCs, we compare the potential energy and vibrational entropy at coexistence.…”