Beads of haematite can pick up and carry other particles more than 10 times their size with the flick of a switch
Ant-like beads of haematite could be the giants of nanoscale construction. Tiny particles of the iron mineral have been made to pick up and carry cargo more than 10 times their size. The feat could be used in targeted drug delivery or building artificial muscles.
Iron-based nanoparticles are ideal cargo-carriers because they can be steered using magnetic fields or by following a thinly etched track. Previous versions relied on chemical glues to pick up stuff, but getting them to drop it has proved difficult.
To tackle that problem, Jérémie Palacci at New York University and his colleagues started by suspending haematite nano-beads and a variety of cargo particles in a hydrogen peroxide solution. Shining a light gave the haematite electrical charge, which broke bonds in the neighbouring solution.
The resulting halo of water and oxygen was not in chemical balance with its surroundings, a disturbance which drew larger particles to the beads. A bead and its cargo could then be steered together. To make the bead release its load, the team simply turned off the light.
"The drop-off has been problematic in other papers. We had to come up with really jerry-rigged situations in order to do it," says Ayusman Sen at Pennsylvania State University in University Park, who was not involved in the new work. "They have a better way of picking up and dropping particles than anyone else." The same iron bead can even be used repeatedly to round up a whole flock of larger particles.
Palacci's team envision using the nano-beads in future micro-manufacturing plants, for instance, to create artificial muscles by laying down the required particles and building fibres along tiny tracks. "That would be really cool," he says. "If you can make that, you can start thinking about everything muscles are used for in biology and try to see if you can mimic it."