doi:10.1038/nindia.2018.65 Published online 25 May 2018
Researchers have synthesised nanorods that can move on their own in a fluidic environment without the need for any external energy1. Chemical reactions on the surface of the nanorods trigger their motion, making them suitable for transporting tiny cargo, such as catalysts, across short distances.
In separate experiments, other researchers have used external stimuli such as chemicals, magnetic fields, light and ultrasound to move tiny particles in fluid. However, the particles showed poor motility in these experiments.
Scientists from the Indian Institute of Science Education and Research, Kolkata, and the Institute of Mathematical Sciences, Chennai, both in India, led by Soumyajit Roy and Ronojoy Adhikari, made the nanorods using ammonium heptamolybdate tetrahydrate, a metal-oxide-based soft material. They then tested the nanorods’ ability to move by adding hydrazine sulphate solution to the nanorods.
The hydrazine solution set off chemical reactions on the surface of the nanorods. These reactions produced nitrogen gas that, in turn, generated an uneven osmotic stress on the fluid that surrounded the nanorods, triggering their motion.
With an increase in hydrazine concentration, the velocity of the nanorods increased, reaching a maximum value at a critical concentration. Above the critical concentration, nanorods’ velocity began to drop. The nanorods were able to retain their motion for three days.
The nanorods could clump together, creating large surface areas – a property potentially useful for making nanocarpets and nanorafts. “In the future, such nanostructures with large surface areas can be utilised to ferry different kinds of micro objects,” says Roy.
1. Mallick, A. et al. Redox reaction triggered nanomotors based on soft-oxometalates with high and sustained motility. Front. Chem. 6, 152 (2018)