DNA-controlled assembly of a NaTl lattice structure from gold nanoparticles and protein nanoparticles

Abstract

The formation of diamond structures from tailorable building blocks is an important goal in colloidal crystallization because the non-compact diamond lattice is an essential component of photonic crystals for the visible-light range. However, designing nanoparticle systems that self-assemble into non-compact structures has proved difficult. Although several methods have been proposed, single-component nanoparticle assembly of a diamond structure has not been reported. Binary systems, in which at least one component is arranged in a diamond lattice, provide alternatives, but control of interparticle interactions is critical to this approach. DNA has been used for this purpose in a number of systems. Here we show the creation of a non-compact lattice by DNA-programmed crystallization using surface-modified Qβ phage capsid particles and gold nanoparticles, engineered to have similar effective radii. When combined with the proper connecting oligonucleotides, these components form NaTl-type colloidal crystalline structures containing interpenetrating organic and inorganic diamond lattices, as determined by small-angle X-ray scattering. DNA control of assembly is therefore shown to be compatible with particles possessing very different properties, as long as they are amenable to surface modification.

Figure 1

DNA-programmable nanoparticle crystallization method: a. Different crystallographic arrangements can be programmed by changing the terminal part of the DNA linker sequence. b. Matching of the effective radii of DNA-linked particles by adjusting the length of the spacer DNA linker to compensate for changes in the Au core particle diameter. Dark rings around DNA coronas indicate the sticky ends of linkers –X and -Y. c. Details of the binary-component assembly system in which AuNPs and VLPs are assembled using two different DNA linkers -X and -Y.

Figure 2

a. Illustration of the NaTl structure, which features two independent and interpenetrating diamond structures. b. Example of morphology changes during aggregation simulation. (From left, t=50.0, 120.0, and 190.0) As time goes on, the size of aggregates increases, and the crystalline structure becomes more well-defined. c. Calculated change in scattering intensity during the simulation. With increasing time the scattering intensity shows more distinctive peak structures, which indicates more well-defined crystallinity. Scattering intensities were calculated using the Debye formula with two different particles. In the calculations, we used the individual scattering intensities of the two different particles (AuNPs and VLPs), which were measured by SAXS experiments (Supporting Information).

Figure 3

a. Rendition of the Qβ virus capsid (from http://viperdb.scripps.edu). b. Interlocking dimer of coat protein subunits (black and gray); 90 such dimers form the capsid structure. The positions of surface-accessible amine groups are shown (orange = N-terminus, red = Lys2, blue = Lys13, green = Lys16); disordered sequences are not. c. Steps for surface derivatization of the Qβ VLP. d. DNA oligomer attached to four different sizes of AuNPs used (10, 15, 20 and 30 nm in diameter) with average DNA loadings of 27, 60, 107, and 240 strands/particle, respectively.

Figure 4

Assembly of an NaTl alloy structure using DNA-linked AuNPs and DNA-linked VLPs. a. Schematic layout of effective particle size including both the core particle and the DNA. For larger core AuNPs, the length of the DNA spacer was decreased, resulting in a constant effective particle size, equivalent to that of the DNA-decorated VLPs. b. SAXS patterns of the NaTl structure generated using this binary system of 10 nm AuNPs (top) and 15 nm AuNPs (bottom). The scattering pattern from 20 nm AuNPs was quite similar to the 15 nm case and is not shown here. c. Integrated data from b indicates the formation of NaTl structures. The x and y axes were normalized to the height and the position, respectively, of the strongest (second) ring. These data show that DNA-directed nanoparticle assembly can combine two very different materials without phase separation behaviour. The integrated one dimensional data shows clear characteristics of an NaTl structure. d. Comparison between the normalized scattering intensity of the 15 nm experimental results and theoretical calculations of the NaTl (blue line) and CsCl (dotted grey line) structures. The relative positions and the relative heights of three peaks (indicated by arrows) are well-matched between theory and experiment.