Fig. 4

Optical properties as a function of the superstructure. a SAXS data showing the formation of the superlattices upon decreasing ionic strength (n _AuNP/n _TMV ~ 25 for all measured data). Data shifted in y-direction for clarity. The arrow indicates the diffraction peak (q ~ 0.02 Å⁻¹) corresponding to the interparticle distance (d ~ 31 nm) of nanoparticles within individual rows of nanoparticles. b Upon decreasing ionic strength, AuNPs are concentrated into the superlattice wires leading to a smaller AuNP interparticle distance. c UV–vis data (scaled for clarity) at different salt concentrations showing the effect of AuNPs assembling tightly in the superlattice as a function of the ionic strength. The plasmonic resonance peak at 524 nm corresponding to free AuNPs disappears completely only at low ionic strength. d CD data (Savitzky–Golay filtered for clarity, original data in Supplementary Fig. 12). CD features appear as the superlattice forms upon decreasing ionic strength. Inset shows the simulated CD spectrum for different directions of light propagation and taken as an average of all directions. e, f The generated nanoparticle model including 400 AuNPs used to model the CD spectrum. The figure indicates that the lattice undergoes a left-handed e or a right-handed f twist depending on the viewing direction