Kenneth Sandhage and his team at the Georgia Institute of Technology, US, coated the pollen grains with several layers of iron oxide by reacting an iron(III) isopropoxide precursor with the sporopollenin outer coating of the pollen. They then heated the coated grains up to 600°C to burn off the original pollen template, and used additional thermal treatments to convert the iron oxide from haematite (Fe2O3) to magnetite (Fe3O4).
The replica particles are identically shaped to the original pollen grains, which allows them to stick to surfaces like polystyrene using van der Waals forces. Because they are magnetic, they are also attracted to metallic surfaces like nickel film. The team say converting pollen into these iron oxide replicas could be a useful way to manufacture adhesive microparticles, which are used in areas such as drug delivery, catalysis and sensing. Pollens come in different shapes and sizes, and replica particles could be made from different materials to tune their chemical properties.
W B Goodwin et al, Chem. Mater., 2013, DOI: 10.1021/cm402226w