Sci-fi writers have long imagined man-machine hybrids with extraordinary powers. However, "super-factories" with integrated nanomaterials can be much closer to reality than cyborgs. Today, scientists report the development of plants capable of making nanomaterials, called metallo-organic structures (MOFs), and the application of MOF as coatings on plants. The augmented plants could potentially serve useful new functions, such as the detection of chemicals or the more efficient collection of light.
The researchers will present their findings today at the 2019 Spring National Meeting and Exposition of the American Chemical Society (ACS).
According to Joseph Richardson, the project's lead researcher, humans have been introducing foreign matter into plants for thousands of years. "An example of this is the dyeing of flowers," he says. "You would immerse a stem of cut flower in a dye, and the dye would be absorbed by the stem and penetrate into the petals of the flower, then you would see those beautiful colors."
Because of their extensive vascular networks, plants readily absorb water and dissolved molecules in fluids. However, it is more difficult for large materials and nanoparticles, such as MOFs, to penetrate the roots. Richardson and his colleagues at the University of Melbourne (Australia) therefore questioned whether they could feed MOF precursors of plants, which plants would absorb and then convert to finished nanomaterials.
MOFs, made of metal ions or aggregates bound to organic molecules, form highly porous crystals that can absorb, store and release other molecules, much like a sponge. The chemists have made thousands of different MOFs up to now, with potential applications ranging from hydrogen storage to greenhouse gas absorption through the delivery of drugs into the body. . The fact that plants make small amounts of these useful compounds in their own tissues could give them new abilities that we do not see in nature.
To find out if plants could make MOFs, Richardson and his colleagues added metallic salts and organic linkers to the water and then placed cuttings or intact plants in the solution. Plants transported the precursors into their tissues, where two different types of fluorescent MOF crystals developed. In a proof of concept experiment, clumps of lotus plants producing MOF detected small concentrations of acetone in the water, as shown by a decrease in the fluorescence of the materials. Based on these results, Richardson is considering whether plant-MOF hybrids could detect explosives or other volatile chemicals, which could be useful for airport security.
In addition to the fact that plants make MOFs, the finished materials could be used as a coating on plants to help them convert harmful ultraviolet (UV) rays into more useful light for photosynthesis. "While we are planning to grow plants in space or on Mars, with no atmosphere or UV bombardment, this could be useful," says Richardson. "Not only does it protect plants against UV rays, but it also turns them into useful energy, especially if you're away from the sun, it's harder to capture all the light needed for photosynthesis."
Researchers have already begun to examine the protective capabilities of nanomaterials and the preliminary data are promising. The team coated luminescent MOF fragments of chrysanthemums and lilyturf, and exposed the plants to ultraviolet light for three hours. Compared to uncoated clippings, plants with MOF showed less wilting and bleaching.
Richardson is now teaming with plant biologists to study the effects of MOFs on plant growth. Until now, they have not noticed any toxicity of nanomaterials. The researchers also want to study whether MOFs could actually help plants grow better, which could lead to applications in agriculture.
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