Fig. 2. All protein-based edible PUFs made of silk and fluorescent proteins.

a Regenerated particulate eCFP, eGFP, eYFP and mKate2 silk produced by silkworm transgenesis via the piggyBac transposase method in which fluorescent proteins and silk (i.e., Bombyx mori) are genetically fused as recombinant proteins. The fluorescent images are acquired with a set of the excitation (λ_ex) and emission (λ_em) wavelengths, as specified on top of each photograph. The scale bar is 5 mm. b Photograph of an edible PUF device in which fluorescent silk microparticles are embedded in a thin silk film. The scale bar is 2 mm. Scanning electron microscopy (SEM) image of fluorescent silk microparticles with zeolite-like shapes. The scale bar is 200 μm. The inset shows a higher magnification SEM image of fluorescent silk microparticles. The scale bar is 50 μm. c The emission spectra of particulate eCFP (cyan solid line), eGFP (green solid line), eYFP (yellow solid line), and mKate2 (red solid line) silk cover a relatively broad wavelength range in the visible light, while the emission peak positions are not overlapped among others. d Confocal fluorescence microscopy images of the corresponding fluorescent silk microparticles under excitation wavelengths of 405, 458, 514, and 561 nm, respectively. The scale bar is 100 μm. The size of fluorescent silk microparticles is 99.3 ± 7.9 μm (mean ± standard deviation) (Supplementary Fig. 3).