Establishing the design rules for DNA-mediated programmable colloidal crystallization

Abstract

The assembly of DNA-programmable colloidal crystals is presented, where the sizes of nanoparticles used vary from 5 to 80 nm and the lattice parameters of the resulting crystals vary from 25 to 225 nm. A predictable and mathematically definable relationship between particle size and DNA length is demonstrated to dictate the assembly and crystallization processes, creating a set of design rules for DNA-based nanoscale assembly.

Figure 1

Programmable assembly of nanoparticles. a) The lattice parameters of DNA-programmed colloidal crystals are tunable via both DNA length and nanoparticle size within a “zone of crystallization” (inbetween the dashed lines), as defined by the ratio of nanoparticle diameter to linking DNA length. b) The DNA design that links nanoparticles together, consisting of: a hexyl-thiol moiety, a dA₁₀ spacer, a particle-linker duplex, a series of “block” spacers (where n=0-4), and a short, self-complementary linker-linker recognition sequence.

Figure 2

The 1D and 2D SAXS patterns for crystals consisting of (a) 10.4 nm AuNPs, unit cell edge length 67.4 nm; (b) 31.3 nm AuNPs, unit cell edge length 151 nm; and (c) 60.9 nm AuNPs, unit cell edge length 183 nm. (Due to the exponential decay of X-ray scattering as a function of scattering vector, the contrast of the 2D SAXS image in (c) was adjusted non-linearly. This did not affect the 1D plot or data analysis.)

Figure 3

The “zone of crystallization”, as defined by the relationship between nanoparticle diameter and DNA length. Black circles indicate that FCC crystals were formed and grey squares indicate that only disordered aggregates were observed.

Figure 4

Differences in nanoparticle size and DNA length govern the crystal formation process. a) The distance between the AuNP surface and the linker recognition unit shows variability as a function of the length of the DNA strand (ΔL). b) The ratios of ΔL versus variability in nanoparticle size (ΔD) for the longest DNA length in which FCC crystals were not observed (data from grey squares, upper left of Fig. 3) and the shortest DNA length in which they were (data from black circles, upper left of Fig.3)—in general, ordered assemblies are only obtained when ΔL ≥ ΔD. c) A plot of ln(C_eff) against 1/T_m values for each DNA-AuNP system shows that the data follow a linear trend; the value of ΔH of hybridization calculated from this plot is within 6.7% of a previously published value for the non-AuNP-bound ^5′CGCG^3′ duplex. d) The k_on values for crystalline (green traces) and non-crystalline (red traces) DNA-AuNP aggregates, demonstrating that only DNA-AuNPs with high values of k_on are able to form crystals. The value of k_off is plotted as a function of temperature (black trace). When the k_on values are large enough (green values, e), the system can reach temperatures high enough to allow for reorganization of the DNA-AuNPs within an aggregate. However, DNA-AuNP systems with relatively low k_on values (red values, e) melt at temperatures too low to allow the AuNPs to form an ordered crystal.