Sci-fi writers have long imagined human machine hybrids that exert extraordinary powers. However, "super plants" with integrated nanomaterials can be much closer to reality than cyborgs. Today, scientists report on the development of plants that can make nanomaterials called metal-organic frames (MOF) and the application of MOF as coatings in plants. Increased plants could perform new useful functions, such as detecting chemicals or collecting light more efficiently.
The researchers will present their findings today at the 2019 Spring Meeting and National Exposition of the American Chemical Society (ACS).
According to the project's principal investigator, Joseph Richardson, Ph.D., humans have been introducing foreign materials into plants for thousands of years. "An example of this is the dyeing of flowers," he says. "You would submerge a stem of a flower cut in a dye, and the dye would be taken through the stem and penetrate the petals of the flowers, and then you would see these beautiful colors."
Due to their extensive vascular networks, plants readily absorb water and molecules dissolved in fluids. However, it is more difficult for larger materials and nanoparticles such as MOFs to penetrate the roots. So Richardson and his colleagues at the University of Melbourne (Australia) wondered if they could feed the plants with MOF precursors, which the plants would absorb and then turn into finished nanomaterials.
MOFs, which consist of metal ions or clusters linked to organic molecules, form highly porous crystals that can absorb, store and release other molecules, such as a sponge. Chemists have made thousands of different MOFs so far, with possible applications ranging from storing hydrogen fuel to absorbing greenhouse gases to administering drugs within the body. Making plants produce small amounts of these useful compounds in their own tissues could give them new abilities that are not seen in nature.
To see if the plants could produce MOF, Richardson and his colleagues added metal salts and organic binders to the water and then placed intact cuttings or plants in the solution. The plants transported the precursors to their tissues, where two different types of fluorescent MOF crystals grew. In a proof-of-concept experiment, cuttings from lotus plants that produce MOF detected small concentrations of acetone in the water, as evidenced by a decrease in the fluorescence of the materials. Based on these results, Richardson plans to explore whether the plant's MOF hybrids could detect explosives or other volatile chemicals, which could be useful for airport safety.
In addition to making plants produce MOF, the finished materials could be used as a coating on plants to help them convert harmful ultraviolet (UV) light into light that is most useful for photosynthesis. "As we contemplate growing crops in space or on Mars, where you do not have an atmosphere and UV rays bombard you, something like this could be useful," says Richardson. "That's because it not only protects plants from UV rays, but also converts them into useful energy, especially as you move away from the sun, it's harder to capture all the light you need for photosynthesis."
Researchers have already begun to examine the protective capabilities of nanomaterials, and the preliminary data are promising. The team covered chrysanthemum and lilyturf cuttings with luminescent MOF and then exposed the plants to UVC light for three hours. Compared to the uncoated cuttings, the plants with MOF showed less discoloration and discoloration.
Now, Richardson is partnering with plant biologists to study the effects of MOFs on plant growth. So far, they have not noticed any toxicity of the nanomaterials. The researchers also want to explore whether MOFs could really help plants grow better, which could lead to applications in agriculture.
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