Figure 2: Multicolour generation and structural modulation of the Phage litmus.

(a) Phages genetically engineered to recognize target molecules through directed evolution, replicate to create identical copies and then self-assemble into coloured matrices composed of quasi-ordered bundled structures. (b) Composite of AFM images from different matrices (bands) of a Phage litmus. Each matrix is composed of quasi-ordered fibre bundles with different diameter and interspacing, and exhibits a different colour. (c) A fabricated Phage litmus exhibiting four distinct colours; orange, green, blue and deep blue (in red box). Changes in relative humidity (RH) result in changes in colours. Depending on the initial phage-bundle structure, each phage matrix swells with a different ratio and exhibits a different colour change. (d) AFM images of the first phage matrix band at 35% RH and 90% RH, respectively. Changes in colour are due to modulation of the phage bundles’ structures. Height profiles of the cross section (dotted lines) showed that bundle diameter increases 104 nm after swelling (Supplementary Fig. 6f). (e) Reflectance spectra (coloured lines) at normal angle and Fourier power spectra (grey bars) of each phage matrix in 35 and 90% RH generally correspond to each other in hue (position of peak) and chroma (shape of peak; a.u., arbitrary units).