Fig. 26.

(A) Superlattice formation of positively charged gold nanoparticles (AuNP) and negatively charged CCMV at different Debye screening lengths, k⁻¹, (adjusted by NaCl concentration), AuNP/CCMV mass ratios (top) and pH (bottom) determined by small angle X-ray scattering (SAXS). At a given pH, the superlattice is formed only in a narrow NaCl concentration window (Region 2), which is shifted to smaller k⁻¹ (i.e. higher NaCl concentration) when the pH is increased. Superlattice formation is possible only when the pH is higher than pI of CCMV (pH = 3.8). High NaCl concentration screens the electrostatic interaction between CCMV and AuNP, resulting in non-assembly of the particles (Region 3). (B) Two-dimensional (inset) and integrated one-dimensional SAXS data obtained from a CCMV superlattice (sample 2 in (A)) (top). The experimental scattering pattern (black trace) matches well with the respective theoretical scattering pattern of an AB₈^FCC-type structure (red and green traces). Crystalline superlattices are also observed with cryo-TEM (bottom). The particles arrange into an AB₈^FCC type lattice, where CCMV (blue) adopts an FCC structure and the voids between the CCMVs are filled with eight AuNPs (yellow) as shown in inset. (C) Crystal structure models and lattice parameters of CCMV–avidin, CCMV–G6 PAMAM dendrimer and CCMV–Au nanoparticle superlattice. Superlattices with different structures are yielded depending on linker molecules, which mediate assembly of CCMV. Parts A and B reproduced from ref. 14 with permission from Nature Publishing Group, copyright 2013. Part C adapted from ref. 15 with permission from Nature Publishing Group, copyright 2014.