Design and fabrication of recombinant reflectin-based multilayer reflectors: bio-design engineering and photoisomerism induced wavelength modulation

Abstract

The remarkable camouflage capabilities of cephalopods have inspired many to develop dynamic optical materials which exploit certain design principles and/or material properties from cephalopod dermal cells. Here, the angle-dependent optical properties of various single-layer reflectin thin-films on Si wafers are characterized within the UV–Vis–NIR regions. Following this, initial efforts to design, fabricate, and optically characterize a bio-inspired reflectin-based multilayer reflector is described, which was found to conserve the optical properties of single layer films but exhibit reduced angle-dependent visible reflectivity. Finally, we report the integration of phytochrome visible light-induced isomerism into reflectin-based films, which was found to subtly modulate reflectin thin-film reflectivity.

At the Intersection of Natural Structural Coloration and Bioengineering

“…Interestingly, although the tertiary structure for full-length reflectins remains unknown (note that while theoretical work suggests the presence of secondary structural features, they have yet to be confirmed experimentally), recent work shows that the abundant internal motif has some secondary structural features which can be modulated with external stimulation [ 58 ]. Moreover, reflectins can be expressed in and purified from bacterial cells, and the resulting protein can self-assemble into a variety of structures, including nanoparticles, microfibers, hexagonal plates, and thin films [ 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ]. Some of these structures can be further modulated by the application of external stimulation [ 58 , 60 , 61 , 63 , 65 , 66 , 67 , 68 , 69 ].…”

“…Moreover, reflectins can be expressed in and purified from bacterial cells, and the resulting protein can self-assemble into a variety of structures, including nanoparticles, microfibers, hexagonal plates, and thin films [ 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ]. Some of these structures can be further modulated by the application of external stimulation [ 58 , 60 , 61 , 63 , 65 , 66 , 67 , 68 , 69 ]. For example, mechanical agitation of nanoparticles has been shown to induce fibrillation for a truncated reflectin variant and the application of a unidirectional mechanical stimulus has been shown to alter the infrared reflectivity of thin films of reflectin [ 58 , 69 ].…”

“…For example, mechanical agitation of nanoparticles has been shown to induce fibrillation for a truncated reflectin variant and the application of a unidirectional mechanical stimulus has been shown to alter the infrared reflectivity of thin films of reflectin [ 58 , 69 ]. Moreover, chemical stimulation can alter the aggregation state of nanoparticles (e.g., by altering the ionic strength of the solution), induce the assembly or disassembly of hexagonal plates (e.g., by introducing or removing aromatic compounds), and alter the relative thickness of thin films of reflectin (e.g., by altering the local humidity or pH) [ 60 , 61 , 63 , 66 , 67 , 68 , 69 ]. Notably, in mammalian cells engineered to produce intracellular reflectin structures, chemical stimulation induced the reorganization of the reflectin aggregates and was able to alter the relative opacity of the cells [ 60 ].…”

“…In general, inorganic materials have been processed via techniques such as two-photon polymerization, colloidal assembly strategies, and top-down lithography [ 70 , 71 , 72 , 73 , 74 ]. However, these techniques cannot be used on more-sensitive proteins, and instead, techniques such as doctor-blading and inkjet printing of thin films, the extrusion of fibers, and solvent-based self-assembly of particles in solution (e.g., organic solvent induced hexagonal plate formation) are more widely used [ 59 , 60 , 65 , 66 , 67 , 68 , 69 , 75 ]. Nevertheless, the development of reflectin-based biophotonic technologies has been largely limited to thin-film-based geometries partially due to the limited knowledge that we have so far of the proteins’ structure, self-assembly, and proclivity for forming aggregates under physiological conditions.…”

“…Nevertheless, solvent, fluorescence, and temperature effects can make it challenging to deconvolute the secondary structures of proteins using Raman spectroscopy [ 83 , 84 ]. In comparison, CD uses differences in the phi and psi angles of the polypeptide backbone to identify relative fractions of alpha-helices, beta-sheets, turns, and random coils [ 65 , 66 , 67 , 68 ]. Recently, methods to cross-correlate simulated CD spectra from computationally simulated structures and experimental CD spectra have provided additional insight into the secondary and tertiary structures of proteins, and in general are excellent tools for the rapid determination of the secondary structures and folding properties of proteins [ 85 , 86 , 87 , 88 ].…”