Fig. 4
From: The development progress of multi-array colourimetric sensors based on the M13 bacteriophage
(a–e Reproduced with permission from Ref. [54]. Copyright 2014, Nature Publishing Group)
Colour band generation and structural modulation regarding gas exposure. a Composite of Atomic force microscopy (AFM) images from different matrices of colour band. Each matrix is composed of quasi-ordered fibre bundles with different diameters and interspacings and exhibits a different colour. b A fabricated colour band 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. c Reflectance spectra (coloured lines) at a normal angle and Fourier power spectra (grey bars) of each phage matrix in 35 and 90% RH; these generally correspond to each other in hue (position of peak) and chroma (shape of the peak; a.u., arbitrary units). d Photographs of the colour band after exposure to hexane, diethyl ether, isopropyl alcohol, ethanol, methanol, and DI water. e Principal component analysis plot of the colour changes resulting from the exposure of the colour band to different VOCs