Highly Selective Bioinspired Colorimetric Sensor Using Genetically Engineered M13 Virus

In nature, evolution creates numerous nanomaterials, of which only the best are chosen and propagated through generations in the form of proteins and genes. Proteins and genes mutually orchestrate spatial and temporal control over the synthesis of organic and inorganic nanomaterials, commonly resulting in hierarchical structures with specific functions.  During natural selection, the ability of manipulation of light to further modify these structures for more adaptive functions has been a critical component of evolutionary pressure. For examples, using an array of inorganic calcite lenses, brittle star collects more light in the abyss; using flickering photonic color from periodic layers of cuticles, Morpho butterfly communicates to each other in long distances; and using hierarchical protein structures in skins or feathers, many birds (i.e, turkeys and ostriches) express tempers. Various inorganic and organic nanomaterial-based photonic crystals have been developed to mimic biological functions through top-down and bottom-up processes. Self-assembled colloidal nanoparticles combined with atomic layer deposition process have been utilized to recapitulate the optical function of the complex butterfly wing characteristics. Magnetic nanoparticles fixed in curable polymer matrices have been used to rapidly create arbitrary shapes and colors. These biomimetic approaches for color manipulation have demonstrated great promises to develop the sensing applications; however, a common limitation of such sensors is their general lack of chemical selectivity, which makes differentiation among similar compounds, due to the difficulty of tailoring their specific functions and performances. Here, we show high selective bio-inspired colorimetric sensors with tunable functions by self-assembly process and directed evolution of a basic building block, M13 phage. We fabricated multi-color matrices using phage through self-assembly processes. The resulting colorimetric phage matrices composed of quasi-ordered phage bundle structures which can exhibit distinct colors in coherent scattering. Colorimetric phage matrices swelled with different rates depending on the initial phage-bundle structures (different colored phage matrices), which can specifically respond to water and various organic solvents in a sensitive manner. Through directed evolution, we imparted trinitrotoluene (TNT) recognition receptors on the phage and induced the specific response of the colorimetric phage matrices to TNT. Using the commonly used handheld device (iPhone) and automated colorimetric image analysis, we could detect the target TNT molecules in 300 ppb scales in a selective manner. Our sensitive and selective colorimetric phage-based sensors promise to establish a rapid, portable, simple but effective detection of various harmful chemical and biological toxins, an initiative step towards the protection of human health and national security.